CAMBRIDGE IGCSE™ CHEMISTRY: COURSEBOOK Exam-style questions and sample answers have been written by the authors. In examinations, the way marks are awarded may be different. Coursebook answers Chapter 1 Science in context: Lord of the rings 1 2 Jupiter and Saturn are the biggest of the planets in our solar system and are made of hydrogen and helium in the gaseous state. There is a progression outwards from the Sun in terms of the structure of the planets. Those nearest the Sun are rocky and relatively small; beyond Mars the planets are gaseous. Hydrogen molecules are the smallest of all the elements and therefore the forces between them are very small. The gas needs to be highly compressed (so that the molecules are close together) and at a very low temperature (so that the molecules are moving slowly) in order for it to condense into a liquid. Questions 1 2 3 1 4 a freezing b boiling c condensation a methane b ethanol and mercury; they have melting points below room temperature, but boiling points above room temperature c the impurity lowers the freezing point of the liquid a a volatile liquid is one that evaporates easily; it has a low boiling point b ethanol > water > ethanoic acid; ethanol is the most volatile, ethanoic acid is the least volatile c B; both the melting point and boiling point are above room temperature; therefore, it is a solid a if heated strongly then the temperature rises very quickly, the melting and boiling points are close together, the liquid stage is not seen as it boils quickly b you would need to heat the solid slowly so that the temperature rise is not too quick; you could use an electrical heater so you can control temperature more carefully; you could use an oil bath to heat the solid and carefully control the temperature so it is kept between the melting point (114 °C) and boiling point (184 °C) of iodine Experimental skills 1.1 1 Substance B is a pure substance as the curve is flat while the substance melts. Substance A is a mixture as there is no single melting point – that region of the curve is sloped. 2 Take temperature readings at shorter time intervals (e.g. every 30 s); use of a digital thermometer would give more accurate readings / use of a temperature sensor linked to a computer would enable the readings to be taken continuously and enable the graph to be plotted as the readings were being taken. The samples can be re-heated and cooled again, allowing duplicate sets of data to be collected. Cambridge IGCSETM Chemistry – Harwood, Millington & Lodge © Cambridge University Press 2021 CAMBRIDGE IGCSE™ CHEMISTRY: COURSEBOOK Chapter 1 continued 10 In a the liquid levels are the same as there is air both inside and outside the porous pot cylinder; in b hydrogen diffuses into the pot faster than air molecules diffuse out because hydrogen molecules have less mass than the air molecules; this produces an increase in pressure inside the pot and so the liquid level is pushed down on the left (and up on the right). Questions Temperature / °C 5 80 liquid freezing 0 solid –20 Time 6 A = solid; B = energy released; C = energy absorbed 7 A = solid; B = liquid; C = liquid and gas (vapour); D = gas Experimental skills 1.2 1 silver iodide 2 silver nitrate + potassium iodide → silver iodide + potassium nitrate 3 the rates of diffusion of silver and iodide ions 4 because the rates of diffusion of the ions are not the same – silver ions are less heavy and so diffuse slightly more quickly Questions 8 9 2 Exam-style questions 1 6 7 8 9 Evaporation of bromine takes place as molecules escape from the surface of the liquid, the gaseous bromine molecules then spread throughout the gas jar to completely fill the container, there are collisions with air molecules, bromine molecules move from a region of high concentration to low concentration and so are completely mixed with the air and at the same concentration throughout. a Methylamine molecules have a greater mass than ammonia molecules and so diffuse more slowly; the white smoke ring will be more central than for ammonia/ hydrogen chloride, slightly to the right of centre as methylamine diffuses slightly faster than hydrogen chloride. b hydrogen bromide (from hydrobromic acid) or hydrogen iodide (from hydroiodic acid) B [1] ; 2 D [1] ; 3 C [1] ; 4 B [1] ; 5 A [1] ; a Moving slowly [1] ; close to each other [1] ; b They vibrate more quickly ; [1] c evaporation ; [1] d changing from liquid to solid ; [1] a evaporation of the liquid [1] ; and diffusion of the gas particles [1] ; b particles moved more slowly [1] ; because the temperature was lower [1] ; a a solid [1] ; is cooling down [1] ; b they are moving more slowly [1] ; and closer together [1] ; c heat comes from the formation of bonds (interactive forces) between the particles [1] ; a ammonia, which is alkaline, reached the indicator first to change its colour [1] ; because it moved faster [1] ; because it was lighter [1] ; b C 50 s ; [1] rate of diffusion is inversely related to the molecular mass ; heavier molecules, such as HCl here, diffuse more slowly than lighter molecules Answers A and D are too short ; answer B too long. Simple proportion would suggest about 73 s, but the rate of diffusion is inversely related to the square root of the molecular mass. Ammonia molecules diffuse 1.46 times as fast as hydrogen chloride molecules. ; [1] Cambridge IGCSETM Chemistry – Harwood, Millington & Lodge © Cambridge University Press 2021 CAMBRIDGE IGCSE™ CHEMISTRY: COURSEBOOK Chapter 2 Getting started 1 2 ‘H’ and ‘O’ are the chemical symbols for a hydrogen atom and an oxygen atom, respectively. Water consists of two hydrogen atoms chemically bonded to one oxygen atom. When atoms join together like this, they form a molecule. A molecule must have more than one atom in it. You may have heard of protons, neutrons and electrons; these are subatomic particles, and they come together to make the many different types of atom. Science in context: Seeing is believing 1 2 The rings are made up of carbon atoms (not many elements can form rings like this); carbon is the basis of the molecules of life because it can form so many different structures. There are 19 atoms in all (count all the corners); arranged in five hexagonal rings. 4 Protons are positively charged and would therefore repel each other / the presence of the neutrons counteracts this repulsion and means that the nucleus can hold together. 5 B 6 21 protons and neutrons; protons and neutrons are both nucleons 7 Chlorine-37 has two more neutrons in the nucleus. 8 A nitrogen atom has 7 protons and 7 electrons and therefore is electrically neutral. All atoms are electrically neutral. Worked example 2.1 1 relative atomic mass of iridium is 192 Ar = (191 × 37.3) + (193 × 62.7) / 100 = 192.3 Answer corrected to three significant figures as this is the accuracy of the data given. 2 That the proportions of the two isotopes are 50:50 (1:1) as the relative atomic mass is exactly midway between the masses of the two isotopes. Experimental skills 2.1 1 The metal present is responsible for determining the colour seen in the flame. The non-metal present is the same in all cases and so cannot be responsible for the change. 2 It is a physical change. 3 It will be the salt which gave the bluest colour flame. The results will depend on which salts you tested. Questions 1 proton = 1, neutron = 1, electron = 0 (or 1 / 1840) 2 15 protons, 16 neutrons, 15 electrons 3 An element is a substance that cannot be broken down into anything simpler by chemical means. Atoms are the particles that make up all substances; they are the smallest particle of an element that shows the properties of that element; they can join together to make molecules. Each element has its own type of atom – the atoms of an element all have the same number of protons and electrons. 3 Cambridge IGCSETM Chemistry – Harwood, Millington & Lodge © Cambridge University Press 2021 CAMBRIDGE IGCSE™ CHEMISTRY: COURSEBOOK Chapter 2 continued 4 Questions 9 a first shell, maximum 2: second shell, maximum 8 b 2,8,8,2 c 8 in both cases 10 6 in both cases 11 a 5 a C has more neutrons in the nucleus ; it has 8 neutrons compared with 6 in 12C [3] b 2,6 ; [1] c i 4 ; [1] ii 4 ; [1] a It is the outer electrons of an atom that give rise to its chemical properties. Same number of electrons in outer shell ; [2] b (70 × 63) + (30 × 65) / 100 = 63.6 ; A and C, they have 4 electrons in their outer shells b D, has 8 electrons in its outer shell c B, has 7 outer electrons d C and D, they have electrons in 3 energy levels e 14; there are a total of 14 electrons in the atom, therefore there must be 14 protons in the nucleus as an atom must be electrically neutral 14 [1 mark for partial working. Answer alone 2 marks] [2] Exam-style questions 1 C ; [1] 2 A ; [1] 3 a b the number of protons in the nucleus of an atom ; mass number is protons + neutrons [2] argon has 2 more neutrons ; c particle charge mass position in atom proton + 1 in the nucleus neutron 0 1 in the nucleus electron − 1/1840 orbiting the nucleus [5] 4 [1] d hydrogen ; [1] e they both have full/complete outer shells ; [1] Cambridge IGCSETM Chemistry – Harwood, Millington & Lodge © Cambridge University Press 2021 CAMBRIDGE IGCSE™ CHEMISTRY: COURSEBOOK Chapter 3 c Science in context: Exploiting the properties of graphene 1 2 There are two forms of carbon that have been known for some time: diamond and graphite. In more recent times the following forms of carbon have been discovered: fullerenes (such as C60 and C70), which are sometimes referred to as bucky balls. This research was extended to discover tubular forms referred to as nanotubes. Most recently, the single-layered form of carbon known as graphene has been isolated. Many of these recently discovered forms show a close relationship to graphite in terms of their properties. Graphite is a layered structure, with each layer being a covalently bonded macromolecule. These layers are very strong and so are very resistant to forces applied at right angles to the layer. However, the layers can slide over each other so a force applied from the side causes the layers to slip. The strength of graphite depends on its orientation. Cl Mg 2+ 7 A 8 A 9 C 10 D Exam-style questions 1 A ; 2 a C ; b the structure shown is of an ionic compound ; potassium bromide is the only ionic compound in the list ; [2] a potassium has lost an electron ; chlorine has gained an electron ; 3 b All the atoms of an element contain the same number of protons (and the same number of electrons). 2 D 3 C 4 C 5 C 6 a 4 F 2− O Na 2 Na + Na + O 5 [1] [2] diagram showing one shared pair of electrons between atoms / 3 pairs non-bonding electrons on each atom ; [2] Cl c covalent ; d KCl high melting point / Cl2 low melting point (or b.p.) ; OR KCl is a solid at room temperature and Cl2 a gas [1] a in calcium chloride solution the mobile ions carry the charge in solution / the ions are fixed in position in the solid ; [2] b by melting it ; c ionic bonds are strong electrostatic forces / intermolecular forces in water are weak interactions ; [2] a graphite has strong covalent bonds between the atoms in the layers / delocalised electrons between the layers of atoms are free to move ; – LiF b 5 [1] Cl Li + – Cl Questions 1 – MgCl 2 [1] [1] [2] Cambridge IGCSETM Chemistry – Harwood, Millington & Lodge © Cambridge University Press 2021 CAMBRIDGE IGCSE™ CHEMISTRY: COURSEBOOK Chapter 3 continued 6 b graphite has layers which can slide over each other ; diamond has a three-dimensional lattice in which all the atoms are bonded ; [2] c i ionic solids have oppositely charged ions that attract each other strongly but when layers are pushed out of line the ions repel each other ; in metals, the metal ions are attracted to a mobile cloud of electrons and so the layers of ions can move ; [2] ii the charged particles in an ionic solid are fixed in position the electrons in a metal lattice are free to move ; [2] Cambridge IGCSETM Chemistry – Harwood, Millington & Lodge © Cambridge University Press 2021 CAMBRIDGE IGCSE™ CHEMISTRY: COURSEBOOK Chapter 4 Science in context: What’s in a name? 1 Lv = livermorium / Fl = flerovium / Cn = copernicium 3 f 3Fe + 4H2O → Fe3O4 + 4H2 a H2 + Cl2 → 2HCl b 2Cu + O2 → 2CuO c Mg + ZnCl2 → MgCl2 + Zn 4 Fl named after the Flerov Laboratory of Nuclear Reactions in Dubna, Russia, where the element was discovered in 1998; (honours the Russian physicist, Georgy Flyorov) Solid sodium carbonate reacts with hydrochloric acid solution to give sodium chloride solution and carbon dioxide gas. Water, a liquid, is also produced. 5 a Ag+(aq) + Cl−(aq) → AgCl(s) b Ba2+(aq) + SO42−(aq) → BaSO4(s) a HCl(aq) + KOH(aq) → KCl(aq) + H2O(l) Cm = curium and Mt = meitnerium are the only two elements named after women. 6 H+(aq) + OH−(aq) → H2O(l) b 176 neutrons Atoms are only very short-lived and so not easy to determine the mass number definitively – may be a number of isotopes. Study of the chemistry and physics of the nucleus – structure of the nucleus and possibility of reaching a zone of more stable elements. 2HCl(aq) + CuCO3(s) → CuCl2(aq) + H2O(l) + CO2(g) 2H+(aq) + CO32−(s) → H2O(l) + CO2(g) Worked examples 4.5 Mass of hydrated magnesium sulfate crystals = 22.50 − 10.20 = 12.30 g Mass of dehydrated crystals = 16.20 − 10.20 = 6.00 g Worked examples 4.1 a CH4 b NCl3 Mass of water combined in crystals = 12.30 − 6.00 = 6.30 g 4.2 a MgI2 b AlBr3 4.6 4.5 g (4.48 rounded to one decimal place) 4.3 a K3PO4 b NH4NO3 4.4 2Na + Cl2 → 2NaCl 1 2 Questions 7 Questions 7 2Al + 3Cl2 → 2AlCl3 Lv named in recognition of the Lawrence Livermore National Laboratory in the United States. Cn named after the Polish astronomer, Copernicus 2 e a iron + oxygen → iron(III) oxide b sodium hydroxide + sulfuric acid → sodium sulfate + water c sodium + water → sodium hydroxide + hydrogen 8 a covalent b ionic c CH4, NaI, C3H6, ICl3, BrF5, HBr a 32 b 17 c 98 a 2Cu + O2 → 2CuO d 119 b N2 + 3H2 → 2NH3 e 188 c 4Na + O2 → 2Na2O a 100 d 2NaOH + H2SO4 → Na2SO4 + 2H2O b 6g 9 Cambridge IGCSETM Chemistry – Harwood, Millington & Lodge © Cambridge University Press 2021 CAMBRIDGE IGCSE™ CHEMISTRY: COURSEBOOK Chapter 4 continued Exam-style questions 1 A ; [1] 2 a H3PO4 (order of elements not critical) ;[1] b magnesium carbonate (s) + phosphoric acid (aq) → magnesium phosphate (aq) + carbon dioxide (g) + water (l) ([1] for substances and [1] for state symbols ;) c 24 + 12 + (3 × 16) = 84 (partially correct calculation = [1] ;) [2] d Relative formula mass is the sum of the relative atomic masses of the elements in a compound. ; [1] e (1.2/6) × 21 = 4.2 g (partial calculation = [1] ;) [2] 3 C ; [1] 4 a C2H4O ; [1] b 88 ; [1] c Mg(s) + 2C3H7COOH(aq) → Mg(C3H7COO)2(aq) + H2(g) ; (state symbols [1] ; formula of magnesium butanoate [1] ; balancing [1] ; correct substances [1] ;) d The sum of the relative atomic masses of the elements in the compound ; [2] [1 mark if only the simpler terms, masses or atomic masses are used.] e 8 magnesium butanoate (or any ionic compound) is not made up of molecules and so cannot have a molecular mass ; [1] Cambridge IGCSETM Chemistry – Harwood, Millington & Lodge © Cambridge University Press 2021 CAMBRIDGE IGCSE™ CHEMISTRY: COURSEBOOK Chapter 5 5.3 mol Mg = 4/24 = 0.167 mol Getting started mol acid = 5.48/36.5 = 0.15 mol The balloons will all contain the same number of characteristic particles (atoms for B and D / molecules for A and C). from equation 1 mol Mg reacts with 2 mol acid therefore 0.167 mol would react with 0.3 mol acid Balloon B will fall fastest; the constituent particles of the gas have the heaviest mass. Science in context: Chemical accountancy and atom economy HCl is the limiting reagent. 5.4 from equation 2 mol Al gives 2 mol aluminium chloride (1 : 1 ratio) mol Al = 4.5/27 = 0.167 mol 1 Other costs: energy costs / safety costs in terms of the physical plant / level of manpower needed / cost of unwanted by-products 2 Marketing should consider uses for the by-products and then convincingly ‘sell’ their usefulness 0.167 mol aluminium chloride = 22.29 g % purity = (17.8/22.29) × 100 = 79.9% 5.5 Percentage by mass of N = 21.2% 5.6 Percentage by mass of water = 62.9% Questions Worked example 4 a 5.1 1 5 The mole is that amount of substance that contains 6.02 × 1023 constituent particles (e.g. atoms, molecules). It is equal to the relative formula mass (relative molecular mass) of a substance in grams. 6 The percentage yield of a product from a reaction is the proportion of the theoretical yield that is actually obtained. The percentage purity of the product of a reaction is a measure of how contaminated the product is. 2 18 g/mol 0.125 mol Questions 1 2 a 0.4 mol b 2.41 × 10 formula units / 2.41 × 10 Na ions and 2.41 × 1023 OH– ions 23 23 + molar ratio of Cu : Fe : S is 1 : 1 : 2 empirical formula = CuFeS2 3 a molar ratio of C : H : O is 1 : 3 : 1 empirical formula = CH3O b molar mass of CH3O = 31 so actual formula is C2H6O2 c HO H H C C H H OH b 18.7% Worked examples 5.7 a 22 g of carbon dioxide = 0.5 mol volume of gas = 12 dm3 b number of moles nitrogen = 1.5 mol mass of nitrogen = 28 × 1.5 = 42 g 5.8 Molar concentration = 0.1 mol/dm3 5.9 a mol acid used = (0.2/1000) × 25 = 0.005 (5 × 10−3) mol Worked examples b molar ratio 1 : 2, so mol NaOH = 0.01 mol 5.2 1 c 0.01 mol NaOH in 10 cm3 32 g methane = 2 mol methane reacting ratio of methane : oxygen is 1 : 2 reacts with 4 mol oxygen = 64 g of oxygen 9 28.2% concentration of NaOH solution = (0.01/10) × 1000 = 1 mol/dm3 Cambridge IGCSETM Chemistry – Harwood, Millington & Lodge © Cambridge University Press 2021 CAMBRIDGE IGCSE™ CHEMISTRY: COURSEBOOK Chapter 5 continued 5 Questions 7 8 9 a 0.02 moles b 2 moles c 0.07 moles a 36 000 cm3 b 1440 cm3 c 12 000 cm3 a 2 mol/dm3 b 0.2 mol/dm3 c 1 mol/dm3 d 0.8 g of NaOH = 0.2 moles; 0.2 mol/dm3 a 0.12/24 = 0.005 mol [1] b 0.005 mol [1] c 1 mol BaCO3 = 137 + 12 + (16 × 3) = 197 g [1] mass of barium carbonate = 0.005 × 197 = 0.985 g [1] % purity = (0.985/1.23) × 100 = 80% [1] d e Exam-style questions 1 D ; 2 a b c 3 4 [1] 40/12, 53.3/16, 6.7/1 = 3.33 : 3.33 : 6.7 empirical formula = COH2 ([1] for each step) ; [3] molecular formula = (COH2) × 2 = C2O2H4 ; [1] 12/60 = 0.2 mol in 250 cm3 / concentration = 0.2 × 4 = 0.8 mol/dm3 ; [2] ([1] for units) [3] a potassium carbonate ; [1] b 0.005, 0.005, 0.42 g ; [3] c (0.35/0.42) × 100 = 83.3% ; [2] a C3H8 + 5O2 → 3CO2 + 4H2O ; [2] ([1] for correct formulae, [1] for balancing) 10 b volume ratio of propane to carbon [2] dioxide is 1 : 3 ; 100 × 3 = 300 cm3 ; (Wrong answer to part a can be carried through to gain marks here.) c 50 cm3 of methane forms 50 cm3 of carbon dioxide ; water condenses at room temperature and pressure so not counted ; excess of oxygen is 50 cm3 so total is 100 cm3 ; [3] Cambridge IGCSETM Chemistry – Harwood, Millington & Lodge © Cambridge University Press 2021 CAMBRIDGE IGCSE™ CHEMISTRY: COURSEBOOK Chapter 6 3 Getting started 1 Wiring is most often made of copper (due to high conductivity and flexibility). 2 Wiring is usually covered in plastic coating to insulate the wires to ensure that the electricity is conducted to where it is intended to go. Plastic is used as the insulator as it is generally flexible which is helpful as it can be easily manipulated and will not crack. 3 Liquid metals do conduct electricity. Other liquids that conduct include molten and aqueous solutions of ionic substances. Experimental skills 6.1 1 Depends on the equipment available but a reliable power pack to adjust the voltage applied is useful / use of an ammeter rather than a light bulb to detect flow of current. 2 The electrodes would need to be thoroughly cleaned with sandpaper / washed in propanone and then dried / weigh the electrodes on as accurate a balance as is available. Science in context: The hydrogen economy 1 2 2H2(g) + O2(g) → 2H2O(g) Questions The reaction is exothermic, generating electrical energy. 4 The fuel cell is considered to be environmentally advantageous as the only emissions are water vapour. However, to be considered carbon-neutral involves a broader range of considerations. These include the origins of the raw materials – particularly the hydrogen and the energy source used to generate it. There is ‘grey hydrogen’ obtained by steam-reforming natural gas, or from electrolysis of water where the electricity is produced by fossil fuel power stations. ‘Green hydrogen’ is hydrogen from the electrolysis of water using electricity generated by solar or wind power. Questions 1 2 11 When a metal conducts electricity it is the delocalised electrons present in the structure that move through the metal to carry the charge / in aqueous solutions of ionic compounds it is the ions present that move to carry the charge. a potassium at cathode and chlorine at anode b hydrogen at cathode and chlorine at anode 5 metal is formed at the cathode and a non-metal at the anode 6 a the object to be plated is made the cathode b copper(II) sulfate solution a 2Br−(l) → Br2(g) + 2e− b because the lead ions have gained electrons 7 8 steam-reforming of methane (natural gas) electrolysis of water using electricity generated by solar or wind power a i, iii, iv and v conduct electricity. 9 b iii and v are electrolytes (aqueous solutions of ionic compounds). 10 2H2(g) → 4H+(aq) + 4e− a The ionic solid does not conduct as the ions present cannot move about (they can only vibrate at fixed positions). b Melt it or dissolve it in water. Cambridge IGCSETM Chemistry – Harwood, Millington & Lodge © Cambridge University Press 2021 CAMBRIDGE IGCSE™ CHEMISTRY: COURSEBOOK Chapter 6 continued Exam-style questions 1 C ; [1] 2 A ; [1] 3 a B; b E; c F; d D; e C ; a i cathode ; [1] ii electrolyte ; [1] 4 5 b arrows pointing (clockwise) away from negative and towards positive ; [1] c dilute sulfuric acid ; [1] d carbon or platinum ; [1] a i cathode gains in mass ; [1] ii anode does not change ; [1] b the blue colour would fade to colourless ;[1] c 4OH− → O2 + 2H2O + 4e− (correct product [1] ; balanced equation [1] ;) d i the anode would lose mass [1] ; / copper anode dissolves to form ions [1] ; cathode increases in mass [1] ; / copper deposited on cathode [1] ; ii the solution colour would not change [1] ; / concentration of copper ions in solution remains the same [1] ; e 12 [5] movement of copper ions [1] ; from anode to cathode [1] ; Cambridge IGCSETM Chemistry – Harwood, Millington & Lodge © Cambridge University Press 2021 CAMBRIDGE IGCSE™ CHEMISTRY: COURSEBOOK Chapter 7 Science in context: Keeping cool! 1 2 CFCs were very stable compounds and were not degraded (broken down) until they reached the upper atmosphere where they released chlorine free radicals. These radicals reacted with the ozone layer protecting the Earth from harmful UV radiation. ‘Holes’ appeared in the upper atmosphere, particularly over the Earth’s poles. CFCs were banned by the Montreal Protocol. CFCs are also greenhouse gases. Use of refrigerants greatly improved food storage and preservation and allowed for the long-distance transportation of foods. Air-conditioning made the workplace much more comfortable in regions of intense or extreme climate. 8 bonds made = (4 × 464) + (1 × 498) enthalpy of reaction = bonds broken – bonds made = −210 kJ/mol reaction is exothermic 9 2 a physical b chemical c physical d physical a exothermic b exothermic c exothermic d endothermic 1 B ; 2 a increase [1] ; b physical [1] ; c increase [1] ; d chemical [1] ; e chemical [1] ; a effervescence/fizzing/bubbles ; [1] b bubbling stops ; [1] c endothermic [1] ; because the temperature goes down [1] ; d exothermic [1] ; products have less energy than the reactants [1] ; a energy to break bonds = 2253 kJ/mol [1] ; energy forming bonds = 2346 kJ/mol [1] ; 3 3 A new substance(s) has been formed. 4 an endothermic reaction For a reaction to take place some bonds in the reacting substances must first be broken. Bond breaking is an endothermic process and therefore there is always a need for some energy to be supplied by the surroundings to start off a reaction. Exam-style questions Questions 1 bonds broken = (4 × 464) + (2 × 144) 4 difference = 93 kJ/mol [1] ; correct sign (−) [1] ; 5 Energy / kJ Zn(s) + CuSO4(aq) ZnSO4(aq) + Cu(s) [1] b +93 kJ/mol ; [2] c [1] for each correct label (see Figure 7.15) ; [2] made activation energy EA lower ; [1] d Progress of reaction 13 6 The energy of the reactants is lower than the energy of the products / upwards arrow. 7 Bond breaking is endothermic. Cambridge IGCSETM Chemistry – Harwood, Millington & Lodge © Cambridge University Press 2021 CAMBRIDGE IGCSE™ CHEMISTRY: COURSEBOOK Chapter 8 Science in context: Studying incredibly fast reactions b There will be more surface area of the solid exposed to the reactant and therefore more frequent collisions. 1 c Greater concentration means there are more reactant molecules present and so there will be a greater frequency of collision. carbon dioxide + water → glucose + oxygen The photosynthesis reaction maintains the level of oxygen in the atmosphere and removes carbon dioxide. The two biochemical processes of photosynthesis and respiration maintain the balance between these two gases that are important for life. Other important reactions include those involved in the making of proteins and the copying of DNA. 2 Exam-style questions 1 B ; 2 a The keys factors in industry are achieving sufficient product in as economic a way as possible. The reaction processes used must give a yield at a reasonable rate as time is an economic cost. The product must also be achieved in a system that is safe and environmentally sustainable. 14 a rate increases b rate increases c rate increases 3 2 The reactions that would spoil the food are slowed down at the lower temperature. 3 at the beginning 4 A catalyst is a substance that speeds up a chemical reaction but is not itself used up in the course of the reaction. 5 biological catalyst 6 manganese(IV) oxide 7 changes in temperature and pH 8 The presence of a catalyst decreases the activation energy of a reaction. 9 a An increased temperature means that the particles are moving faster and will therefore collide more frequently; when they collide, more particles will have energy greater than the activation energy so there will be more collisions that result in a reaction. 4 because the reaction is complete (has stopped) ; b 20/30 = 0.67 [1] ; unit cm3/s [1] ; c gas syringe ; d any two from: Questions 1 [1] a [1] [1] • increase temperature ; • smaller pieces of calcium carbonate ; • more concentrated acid ; the rate of reaction is inversely proportional to the time for the cross to disappear ; [2] [1] b as the temperature increases the cross is obscured (becomes hidden) in a shorter time / the reaction rate increases with temperature so the cross becomes hidden faster ; [2] c the reaction rate increases with an increase in temperature because the particles are moving faster and so collide more frequently [1] ; / the particles have more kinetic energy and so more collisions involve energy greater than the activation energy [1] ; / more collisions produce a reaction [1] ; a smaller particles have a larger surface area [1] so there are more collisions [1] ; b collisions are more frequent [1] ; and a higher proportion have sufficient energy to react [1] ; c copper acts as a catalyst [1] ; catalysts are not consumed by the reaction [1] ; d hydrogen is a very light gas [1] ; so the change in mass is not sufficient to be detected [1] ; Cambridge IGCSETM Chemistry – Harwood, Millington & Lodge © Cambridge University Press 2021 CAMBRIDGE IGCSE™ CHEMISTRY: COURSEBOOK Chapter 9 Getting started 1 A crop is a plant that is grown on a large scale in order to sell it. 2 This answer will depend on where learners live but could include a type of cereal, fruits or vegetables. 3 Crops need sunlight and water but also nutrients. 4 A fertiliser contains the nutrients that plants need. It can be added to soil to improve plant growth. 5 Increasing the temperature favours the endothermic process, so the equilibrium position will move to the right. / The equilibrium counteracts the external change in conditions so the endothermic process absorbs the heat being supplied. a Hydrogen is obtained by the steamreforming of methane: CH4(g) + H2O(g) → CO(g) + 3H2(g) b burning sulfur or the roasting of metal sulfide ores such as zinc sulfide S(s) + O2(g) → SO2(g) An organic fertiliser is made of a natural product such as manure. An artificial fertiliser is manufactured. Science in context: Revolutionising food production 2ZnS(s) + 3O2(g) → 2ZnO(s) + 2SO2(g) 6 c the air a 450 °C / iron catalyst / 20 000 kPa pressure b Increased pressure would produce more ammonia. 1 Iron is a much more readily available metal and more economically suitable. c Increased temperature would yield less ammonia. 2 Apart from cost, there are environmental issues involved in mining for the rarer metals as such mining often involves development in environmentally sensitive areas. d The unreacted nitrogen and hydrogen are recirculated so that they can further react to give more ammonia / so that they react the second time around (saves producing more raw materials). a to replace nutrients that have been lost from the soil by plant growth / to increase crop yield b because these are the three elements needed by plants, which can become used up in soil a nitric acid and ammonia (ammonium hydroxide) b phosphoric acid and ammonia (ammonium hydroxide) c sulfuric acid and ammonia (ammonium hydroxide) Questions 1 a The white powder turns blue. b as a test for the presence of water c CuSO4(s) + 5H2O(l) → CuSO4.5H2O(s) 2 Test to see that it boils at 100 °C. 3 The reverse reaction to form the anhydrous salt requires heat (is endothermic); therefore, the reaction to add water back must give out heat (exothermic). 4 15 5 b a i There is no effect as there are the same number of moles of gas on both sides of the equation. ii Increasing pressure will move the position of the equilibrium to the right, more NO2 7 8 9 They are washed off fields by rain and end up in streams and rivers / algal growth / eutrophication / acidification of soils by excessive use of nitrates. Cambridge IGCSETM Chemistry – Harwood, Millington & Lodge © Cambridge University Press 2021 CAMBRIDGE IGCSE™ CHEMISTRY: COURSEBOOK Chapter 9 continued Exam-style questions 1 reversible reaction ; b turns green/blue [1] ; and gets hot [1] ; c anhydrous [1] ; cobalt chloride turns pink [1] ; [1] 2 B ; [1] 3 C ; [1] 4 a advantage: increases rate [1] ; disadvantage: causes decomposition of ethanol [1] ; b makes particles closer together (more collisions) [1] ; moves equilibrium to the right (forward) [1] ; c to speed it up ; [1] d none ; [1] e ethanol is constantly removed from the reactor [1] , which draws reaction to the right (so reverse reaction doesn’t happen) [1] ; a nitrogen from the air [1] ; hydrogen from methane/water [1] ; b A higher temperature would make the reaction faster [1] ; but would also move equilibrium position to the left (move reaction backwards) [1] ; c Higher pressure is costly to produce ; [1] d The catalyst becomes poisoned / doesn’t work as efficiently ; [1] e The catalyst is finely divided or pelleted to increase the surface area so that more of the reactant gases can attach and react together. ; [1] 5 16 a Cambridge IGCSETM Chemistry – Harwood, Millington & Lodge © Cambridge University Press 2021 CAMBRIDGE IGCSE™ CHEMISTRY: COURSEBOOK Chapter 10 Getting started • Oxygen is the gas in the air that is involved in burning magnesium and hydrogen popping when ignited. • Reduction is the loss of oxygen. 7 Science in context: Fuelling the international space programme 1 2 Redox reactions are usually used to drive an engine or as an explosive reaction. Very fast reactions / producing a large amount of energy / rapid expansion in volume. The products of an explosive reaction are likely to be gaseous. 1 A, B and D 2 A and B 3 reduction 4 a b 6 17 9 N2H4(g) + O2(g) → N2(g) + 2H2O(g) 1 An oxidising agent is a substance that will oxidise (add oxygen to) another substance and is itself reduced during a redox reaction. Examples: oxygen / hydrogen peroxide / chlorine / potassium manganate(VII) A reducing agent is an element or compound that will reduce (remove oxygen from) another substance and is itself oxidised during a redox reaction. Examples: hydrogen / carbon / carbon monoxide / a reactive metal Reduction is the gain of electrons; oxidation is the loss of electrons. During a redox reaction the oxidising agent gains electrons; the oxidising agent is itself reduced during the reaction. a No, even in a reaction such as the burning of magnesium the magnesium is obviously oxidised, but the oxygen has been reduced in that it is no longer the free element. a +3 b +5 c 0 d +3 e +6 a Zn2+ ions b Br2 c MnO4− b colourless to yellow-brown / c purple to colourless Exam-style questions Questions 5 8 b The definition involving gain or loss of oxygen is the more straightforward to understand; but that based on electrons includes more reactions, and is more useful in that sense. a C ; [1] b B ; [1] 2 B ; 3 a F ; [1] b A ; [1] c C ; [1] d B or F ; [1] e D ; [1] f E ; [1] g F ; [1] a potassium manganate(VII) [1] ; b iron(II) sulfate [1] ; c Fe3+ [1] ; d Chlorine is an oxidising agent and so oxidises iodide ions to iodine molecules (electrons have been lost). The chlorine molecules are reduced to chloride ions (electrons have been gained). ; [2] 4 [1] Cambridge IGCSETM Chemistry – Harwood, Millington & Lodge © Cambridge University Press 2021 CAMBRIDGE IGCSE™ CHEMISTRY: COURSEBOOK Chapter 10 continued 5 18 a +2 ; [1] b −2 ; [1] c 0 ; [1] d +4 ; [1] e −3 ; [1] f +6 ; [1] Cambridge IGCSETM Chemistry – Harwood, Millington & Lodge © Cambridge University Press 2021 CAMBRIDGE IGCSE™ CHEMISTRY: COURSEBOOK Chapter 11 Science in context: The significance of language 1 2 Many of these terms come from what was an impressive age of Islamic science and mathematics centred around the Mediterranean (including southern Spain). Modern terms such as algebra have an Arabic origin. The period was linked to the practice of alchemy, which included some truly experimental science together with the more mystical aspects and practices. Strong alkali needs to be removed from soap as it causes skin burns and can be particularly dangerous for the eyes. Modern soaps do have an interestingly wide range of pH. Most are not actually neutral (pH = 7.0). It is worth investigating; same are slightly acidic, while others are mildly alkaline. 6 potassium hydroxide and ammonium hydroxide 7 a blue b S(s) + O2(g) → SO2(g) c magnesium + oxygen → magnesium oxide 8 Al2O3(s) + 6HCl(aq) → 2AlCl3(aq) + 3H2O(l) Al2O3(s) + 2NaOH(aq) → 2NaAlO2(aq) + H2O(l) 9 2 a A corrosive substance ‘eats’ things away. b citric acid c ethanoic acid a It changes its colour depending on whether it is in an acidic or alkaline solution. b alkaline ii neutral iii alkaline iv acidic 3 pH 1 is more acidic (1000 times more acidic than pH 4). 4 a H2SO4 b HCl a They are equal. b hydroxide ion, OH− c i hydrogen ions and nitrate ions ii calcium ions and hydroxide ions iii ammonium ions and hydroxide ions 5 19 i zinc hydroxide or aluminium hydroxide zinc hydroxide + sodium hydroxide → sodium zincate + water Zn(OH)2(s) + 2NaOH(aq) → Na2ZnO2(aq) + 2H2O(l) Questions 1 An amphoteric oxide is one that will neutralise both an acid and an alkali to give a salt and water only. or aluminium hydroxide + sodium hydroxide → sodium aluminate + water Al(OH)3(s) + NaOH(aq) → NaAlO2(aq) + 2H2O(l) Experimental skills 11.1 1 You need to consider the effectiveness of the whole tablet and then the mass of powder used. You need to work out a value for how much acid has been neutralised per unit mass of the tablet. 2 For example: magnesium hydroxide + hydrochloric acid → magnesium chloride + water calcium carbonate + hydrochloric acid → calcium chloride + carbon dioxide + water Mg(OH)2 + 2HCl → MgCl2 + H2O 3 To make the solid more accessible to the acid and to speed up the reaction. Cambridge IGCSETM Chemistry – Harwood, Millington & Lodge © Cambridge University Press 2021 CAMBRIDGE IGCSE™ CHEMISTRY: COURSEBOOK Chapter 11 continued Questions 10 An acid is a proton donor; a base is a proton acceptor. 11 a b 12 a b i CuO(s) + 2HNO3(aq) → Cu(NO3)2(aq) + H2O(l) ii Zn(s) + 2HCl(aq) → ZnCl2(aq) + H2(g) Zn has lost electrons and H+ ions have gained electrons; Zn atoms have been oxidised. b CH3COOH(aq) CH3COO-(aq) + H+(aq) ([1] ; for equation, [1] ; for reversible arrow) ; c Al2O3 + 6HCl → 2AlCl3 + 3H2O ([1] ; for compounds, [1] ; for balancing) d Amphoteric ; e marking points as follows: • aluminium hydroxide is insoluble in water ; • aluminium hydroxide dissolves in sodium hydroxide solution / it is amphoteric ; • the reaction is reversible ; • hydrochloric acid makes the reaction go backwards / equilibrium shifts to left ; [Max. 3] HCl(g) + aq → H (aq) + Cl (aq) + − Hydrochloric acid is fully dissociated into ions (it is a strong acid); ethanoic acid is a weak acid (only partially dissociated into ions); so, there will be more ions present in the hydrochloric acid solution and the electrical conductivity will be higher. [1] Exam-style questions 1 B ; [1] 2 D ; [1] 3 a red ; b calcium carbonate (s) + hydrochloric acid (aq) → calcium chloride (aq) + water (l) + carbon dioxide (g) ([1] ; for compounds, [1] ; for state symbols. ;) c limewater turns milky/cloudy ; [1] d carbon dioxide is an acidic oxide (or simply acidic) ; [1] 4 20 [1] e metal oxides are basic [1] ; non-metal oxides are acidic [1] ; f test with universal indicator [1] ; note colour change [1] ; compare with colour chart to find pH value [1] ; a H2SO4(aq) → 2H+(aq) + SO42−(aq) ([1] ; for substances, [1] ; for state symbols, allow H2SO4(l) and equations involving water molecules as long as they are balanced. ;) Cambridge IGCSETM Chemistry – Harwood, Millington & Lodge © Cambridge University Press 2021 CAMBRIDGE IGCSE™ CHEMISTRY: COURSEBOOK Chapter 12 2 Getting started • It is sometimes called table salt because people add salt to their food. The salt is placed in a container on the table. • Salt is necessary for the regulation of many bodily functions including maintaining the body’s overall balance of fluid. • 1 2 2 3 Salt (sodium chloride) is present in the body and is soluble in water. Loss of salt produces muscle cramps. It is replaced by drinking isotonic drinks (isotonic means the same ion concentration as in our cells). 5 6 7 a magnesium chloride b calcium nitrate c zinc sulfate a to make sure all the acid is reacted/used up b filtration c pipette, burette d yellow e If heated too strongly, the salt could dehydrate (lose water of crystallisation) or even decompose. a method B b sulfuric acid c zinc + sulfuric acid → zinc sulfate + water a Precipitation is the sudden formation of a solid when two solutions are mixed, or a gas passed into a solution. b A method in which an acid solution and an alkali are reacted precisely to produce a salt solution; the salt can be crystallised from the solution produced. c An ionic equation includes just those ions and molecules that actually take part in the reaction. a sulfuric acid b nitric acid c carbonic acid a sodium hydroxide and hydrochloric acid b calcium hydroxide and nitric acid c ammonia (ammonium hydroxide) and sulfuric acid a nitric acid 8 A and C / silver iodide and lead(II) chloride b potassium sulfate and ammonium nitrate 9 a sodium sulfate b white c Ba2+(aq) + SO42−(aq) → BaSO4(s) Experimental skills 12.1 1 4 To preserve food / to add flavour (saltiness is one of the basic human senses) / some cultures use soy sauce, fish sauce or oyster sauce to flavour food rather than table salt. Questions 1 Questions Salt may be found dissolved in seas and oceans. Salt can also be found in rocks (rock salt). Science in context: The significance of salt That the copper oxide was present in excess / this makes sure that all the acid is reacted / this is important as the solution is concentrated by heating after filtration, and hot, concentrated acid is dangerous. copper(II) oxide + sulfuric acid → copper(II) sulfate + water CuO + H2SO4 → CuSO4 + H2O 21 Cambridge IGCSETM Chemistry – Harwood, Millington & Lodge © Cambridge University Press 2021 CAMBRIDGE IGCSE™ CHEMISTRY: COURSEBOOK Chapter 12 continued Exam-style questions 1 B ; 2 a sodium chloride or copper sulfate ; sodium too reactive and so unsafe / copper does not react with dilute acids [1] b sodium chloride ; [1] c barium sulfate ; [1] d potassium carbonate ; [1] a bubbles / effervescence / fizzing ; [1] b to ensure all the sulfuric acid was reacted / used up ; [1] fizzing would stop, or excess solid remained ; [1] 3 c d filter [1] ; heat to crystallisation point [1] ; separate/dry crystals [1] ; 4 A ; 5 a lead nitrate [1] ; sodium, potassium or other soluble chloride [1] ; b mix solutions of the substances [1] ; filter and keep the residue [1] ; wash the residue [1] ; dry the residue [1] ; a insoluble calcium sulfate [1] ; stops the acid reaching the carbonate [1] ; b use hydrochloric or nitric acid instead ;[1] c sodium, potassium, copper or magnesium ; 6 22 [1] [1] [1] Cambridge IGCSETM Chemistry – Harwood, Millington & Lodge © Cambridge University Press 2021 CAMBRIDGE IGCSE™ CHEMISTRY: COURSEBOOK Chapter 13 Science in context: The women behind the Periodic Table 1 Discuss the historic social and religious attitudes to the role of women in society in different parts of the world – their role and access to education; and opportunity to pursue an independent career. 2 Consider the modern situation in different cultures and the development of attitudes, opportunities and perceptions. 1 potassium hydroxide 2 lithium + water → lithium hydroxide + hydrogen a b chlorine of the ones available in a school lab (and fluorine) 5 They all have 8 electrons in their outer shell, except for helium in the first period, which has the maximum possible of 2. 7 23 Rubidium will react more strongly with water than potassium. a C b PH3 sodium, Na b silicon, Si Alkali metals are soft, transition metals are hard / alkali metals have low density, transition metals have high density / alkali metals have just one valency (oxidation number), transition metals show variable oxidation number / alkali metal compounds are white solids, transition metal compounds are coloured. 10 D 1 D ; [1] 2 B ; [1] 3 a iodine ; [1] b lithium ; [1] c bromine ; [1] d potassium [1] ; chlorine [1] ; a false ; [1] b false ; [1] c true ; [1] d true ; [1] e true ; [1] a they have coloured compounds [1] ; they act as catalysts [1] ; they have variable oxidation states [1] ; b CrO is ionically bonded [1] ; CrO3 is covalently bonded [1] ; c amphoteric ; approximately 40 °C (note that the difference between one element and the next is getting smaller as we go down the group) 4 6 9 a Exam-style questions Questions 3 8 4 5 The elements move from metallic character in the first two or three groups to non-metallic character; the non-metallic elements in the centre of the period are giant covalent solids, moving to simple molecular gases on the right of the period. [1] Cambridge IGCSETM Chemistry – Harwood, Millington & Lodge © Cambridge University Press 2021 CAMBRIDGE IGCSE™ CHEMISTRY: COURSEBOOK Chapter 14 Science in context: Smart alloys remember that shape! 8 1 9 2 The name is made up of the chemical symbols of the elements in the alloy: nickel (Ni) and titanium (Ti), and the initials of the Naval Ordnance Laboratory (NOL). They are good conductors of heat and electricity / flexible without breaking / corrosion resistant / biocompatible. 2 3 a 24 b plastic a any two from iron, chromium and nickel b hardness and corrosion resistance Exam-style questions 1 C ; [1] 2 D ; [1] can be beaten into sheets / gives a ringing sound when hit / conducts heat well / conducts electricity well b is an insulator / has a dull surface a graphite b sodium and potassium c mercury d diamond Metals conduct electricity / metals are malleable and ductile. 4 The fact that there are mobile, delocalised electrons in the structure of a metal means that they conduct electricity. Metallic bonding means that the layers of metal ions in the structure can move over each other without the bonding breaking; therefore they are malleable and ductile. 4 B 5 copper and silver 6 a metal + water → metal hydroxide + hydrogen b metal + steam → metal oxide + hydrogen c i Mg + H2O → MgO + H2 ii 3Fe + 4H2O → Fe3O4 + 4H2 7 copper 3 Questions 1 a a D b brass or steel 5 Property Metals Non-metals They conduct electricity True False They react with oxygen in the air True True They are brittle False True They can easily be bent and shaped True False They have high melting points True False [1 mark for each row correct] ; [5] a Its low density ; [1] b Its resistance to corrosion ; [1] c Because of its low density ; [1] d Copper [1] ; Because it is a better conductor [1] ; e Alloy ; Conductor ; Metal ; Mixture ; [1 mark for each correct answer] f It does not rust/corrode [1] ; it is an alloy containing chromium and nickel [1] ; a layers of atoms / ions can slide over each other ; [4] [1] b the larger atoms prevent layers sliding over each other. ; [1] c Yes [1] ; Electrons are still free to move around the metal ions [1] ; Cambridge IGCSETM Chemistry – Harwood, Millington & Lodge © Cambridge University Press 2021 CAMBRIDGE IGCSE™ CHEMISTRY: COURSEBOOK Chapter 15 Science in context: The search for longer-lasting battery power 6 1 7 2 Modern batteries depend increasingly on relatively rare metals such as cobalt. This means that there is pressure to exploit mineral deposits in environmentally sensitive areas, e.g. Alaska. These resources will be depleted rapidly if batteries continue to be used disposably. Graphite rods are used in batteries. Mg(s) + Cu2+(aq) → Mg2+(aq) + Cu(s) D 2 a hydrogen b 3 1 C ; 2 a bubbles/fizzing/effervescence [1] ; / magnesium dissolves [1] ; b no reaction (accept very slow bubbles) ; 2 [1] iron, unknown metal, magnesium, calcium [2] ; (one out of order [1] ;) potassium hydroxide d zinc ; c sodium + water → sodium hydroxide + hydrogen e burning splint [1] ; pops [1] ; (glowing splint pops = [1]) ; d 2K + 2H2O → 2KOH + H2 a aqueous copper sulfate ; [1] a strong and has a low density b iron ; [1] b Aluminium is coated with a very thin oxide layer that protects it from corrosion. c Cu(s) + 2AgNO3(aq) → Cu(NO3)2(aq)+ 2Ag(s) ; c copper 3 Carry out the experiments in polystyrene cups to prevent heat loss or lag the boiling tube with cotton wool / take more frequent temperature readings to find the maximum temperature reached more accurately. d 4 copper becomes coated with silver coating ; solution changes from colourless to blue [2] e zinc is more reactive than copper ; [1] a zinc is the reducing agent / it removes oxygen from CuO ; [2] zinc atoms lose electrons to become Zn2+ ions / Cu2+ ions gain electrons to become copper atoms ; [2] b c 4 magnesium + copper(II) sulfate → magnesium sulfate + copper 5 Magnesium becomes coated with a layer of copper / the colour of the blue solution fades. [1] [1 mark for substances, 1 mark for balancing, 1 mark for state symbol] [3] The reaction would be exothermic, but the rise in temperature would not be as great as that observed when zinc reacts with copper(II) sulfate solution. Questions 25 [1] c Experimental skills 15.1 1 This question is speculative – look at the first letters of the metals in order and see if you can think of a phrase or sentence! Exam-style questions Questions 1 Mg(s) + CuSO4(aq) → MgSO4(aq) + Cu(s) magnesium is more reactive than zinc / it is more ready to form positive ions than zinc / so it removes oxygen from copper(II) oxide more readily than zinc ; [2] Cambridge IGCSETM Chemistry – Harwood, Millington & Lodge © Cambridge University Press 2021 CAMBRIDGE IGCSE™ CHEMISTRY: COURSEBOOK Chapter 16 Science in context: Mining the ocean floor 1 2 The metallic nodules are rich in the metals in demand and it would be relatively easy to extract the required metals. There are various different sites in different regions of the ocean floor. The damage to the ocean floor itself through what is effectively open-cast mining would be significant, as would the damage to the habitat of marine species about which we know relatively little. The dependence on a single land-based source is open to political and economic dangers; and could lead to exploitation of the local population and create socio-economic tensions. 9 Exam-style questions 1 D ; [1] 2 B ; [1] 3 a hematite ; [1] b carbon monoxide ; [1] c because of the high temperature in the furnace ; [1] Experimental skills 16.1 1 The formation of red-brown copper metal. 2 2CuO + C → 2Cu + CO2 4 Questions 1 carbon monoxide iron(III) oxide + carbon monoxide → iron + carbon dioxide Fe2O3 + 3CO → 2Fe + 3CO2 3 silicon(IV) oxide + calcium oxide → calcium silicate SiO2 + CaO → CaSiO3 4 26 d calcium oxide/carbonate [1] ; reacting with impurities in the ore [1] ; a the air ; [1] b it produces the heat needed in the furnace ; the carbon dioxide is then reduced in the furnace to give carbon monoxide [2] To combine with the silicon(IV) oxide (sand) and remove it as slag CaCO3(s) → CaO(s) + CO2(g) 2 Zinc is more effective because if the surface layer is broken the zinc will still protect the steel beneath as it is more reactive than iron (sacrificial protection) / chromium will not protect if the layer is broken as it is less reactive than iron. Because of the high cost of electricity, which is needed in large quantities / also the carbon anodes need replacing regularly. 5 The cryolite lowers the melting point of the electrolyte / because this makes the temperature needed to melt the aluminium oxide much lower. 6 Because the oxygen produced at the anode causes the graphite anodes to burn away as carbon dioxide. 7 water and air (oxygen) / salt water or acid rain 8 painting / greasing / covering with plastic 5 c from oxygen ions [1] ; discharged at the anode [1] ; d The carbon anode burns away [1] ; and so has to be replaced [1] ; e It reacts with the silica (silicon dioxide) impurity in the ore [1] ; forming calcium silicate slag [1] ; a galvanisation ; [1] b it is more resistant to damage but still protects even if the zinc layer is scratched or broken ; [1] c the zinc or magnesium is more reactive than iron [1] ; these metals more readily form positive ions than iron [1] ; so they are corroded rather than the iron / sacrificial protection [1] ; d Aluminium does not corrode because it has a natural surface layer of aluminium oxide. [1] ; This protects the metal by preventing it coming into contact with air. [1] ; Cambridge IGCSETM Chemistry – Harwood, Millington & Lodge © Cambridge University Press 2021 CAMBRIDGE IGCSE™ CHEMISTRY: COURSEBOOK Chapter 17 Science in context: The growing problem of air pollution 1 2 Possible reasons include population density (the greater the number of people, the higher the levels of pollution will tend to be), presence of particular types of industry (living closer to large factories will generally mean poorer air quality), impact of events such as forest/bush fires, government initiatives to reduce levels of airborne pollution, etc. Factors that might encourage more environmentally friendly options include education (an understanding of the problems caused to the environment), tax incentives (reducing the cost of more environmentally friendly solutions), cost savings (switching off electrical equipment when not in use is both good for the environment and saves money), etc. Factors that might prevent more environmentally friendly options include cost (too expensive), habit (used to always using the car / not walking), inconvenience (easier to drive on a wet day than walk), lack of education, etc. Questions 1 nitrogen 78%, argon 0.9% and oxygen 21% 2 Harmful to life both on land and in the water / Increased acidity levels in lakes can kill fish and other aquatic life / Can kill forests (many plants are extremely sensitive to pH) / Some building materials will be damaged/corroded. 3 4 27 8 a methane + oxygen → carbon monoxide + water b 2C6H14 + 13O2 → 12CO + 14H2O Oxides of nitrogen are formed when nitrogen from the air reacts with oxygen at a high temperature (e.g. in a car engine). They are linked to the formation of acid rain and photochemical smog. 5 2CO + 2NO → 2CO2 + N2 6 Carbon dioxide: product of the combustion of fossil fuels. Methane: waste product from livestock (cattle) and landfill sites. 7 Increased use of fossil fuels. Rising sea levels so increased flooding and faster rates of coastal erosion / changes to the life cycles and migratory patterns of animals and birds / more severe droughts and crop failure / drying out of grasslands increases the frequency and severity of wildfires / more frequent and severe weather patterns. Strategies include reducing use of fossil fuels for transportation and electricity generation (e.g. by using renewable sources of energy such as wind and solar) / phasing out of diesel and petrol cars and replacing with electric cars / remove CO2 from the atmosphere / reduce meat consumption / better separation of household waste. 9 Greenhouse gases absorb and re-emit the longer wavelength radiation reflected from the Earth’s surface. 10 Cobalt chloride paper: colour change from blue to pink. Alternatively, anhydrous copper(II) sulfate: colour change from white to blue. 11 Measure melting or boiling point. For pure water, the melting point is 0 °C and the boiling point 100 °C. 12 When nitrates and phosphates enter waterways there is rapid growth of algae. This can block out sunlight and lead to the death of aquatic plants, which will reduce levels of oxygen in the water and so also kill aquatic animals. 13 Useful metals include calcium (supports the health of teeth and bones) and iron (needed for the production of haemoglobin in red blood cells). Problem metals include lead (which can cause liver and kidney damage) and mercury (which has been linked to damage of the nervous system). 14 The majority of current plastics are not biodegradable and are creating pollution, especially in waterways. Biodegradable plastics will break down naturally. 15 Microplastics removed by filtration using a fine sand filter. Dissolved organic compounds removed by an activated carbon filter. Microbes are removed by disinfection using chlorine. Cambridge IGCSETM Chemistry – Harwood, Millington & Lodge © Cambridge University Press 2021 CAMBRIDGE IGCSE™ CHEMISTRY: COURSEBOOK Chapter 17 continued Exam-style questions 1 C ; 2 a 78% ; [1] b Any two from argon, carbon dioxide, other noble gases (neon, krypton and helium) ; [2] i B ; [1] ii A ; [1] iii C and D ; [2] iv C ; [1] c 3 [1] a desulfurisation / scrubbing [1] ; using calcium oxide [1] ; b the air [1] ; c oxides of nitrogen and sulfur cause acid rain [1] ; this causes acidic lakes / rivers [1] ; d i ii e Not enough oxygen / air for complete combustion ; [1] It is toxic ; [1] The toxic gases produced in the engine are converted into less harmful gases before they are emitted into the atmosphere. The process uses a transition metal catalyst [1] ; 2CO + 2NO → 2CO2 + N2 ; [1 mark, other balanced equations showing correct substances are acceptable] [1] 4 B ; 5 a [1] photosynthesis [1] ; 6CO2 + 6H2O → C6H12O6 + 6O2 ; [1 mark for substances, 1 mark for balancing] 28 [2] b methane [1] ; livestock or landfill [1] ; c They are greenhouse gases [1] ; / Heat from the Sun passes through the atmosphere [1] ; / Greenhouse gases prevent some of it from escaping back into space [1] ; / The global temperature increases [1] ; [Max. 3 marks] Cambridge IGCSETM Chemistry – Harwood, Millington & Lodge © Cambridge University Press 2021 CAMBRIDGE IGCSE™ CHEMISTRY: COURSEBOOK Chapter 18 7 Science in context: Building a space elevator 2 The advantages of a space elevator are seen in terms of the ease of transfer of astronauts and goods to the space station without the need for rocket launches from the Earth. Indeed, subsequent exploration from the space station would be easier since there would be no need for the technology to escape the Earth’s gravity. These different forms of carbon all conduct electricity because of the mobile, delocalised electrons associated with the layered structure (see Chapter 3). H H C H H H methane 3 H H H c propanol d butanoic acid a CH3CH(OH)CH3 b CH3CH=CHCH3 c CH3COOC3H7 Structural isomerism is a property of compounds that have the same molecular formula but different structural formulae; the individual compounds are known as structural isomers. C C C C H H H H 150 H 100 C H The bromine water is decolourised from orange-brown to colourless. There would be no change if ethane was bubbled into bromine water. The test is for unsaturation (a C=C): ethene is unsaturated, but ethane is saturated. a a carbon–carbon double bond, C=C b a hydroxyl group, –OH c a carboxylic acid group, –COOH 50 H H C C H H C 1 B; 2 a C ; [1] b A and E ; [2] c a carbon–carbon double bond ; [1] d molecule must contain at least one carbon–carbon double or triple bond ; [1] e C3H6 and CH2 ; O O 0 1 2 3 4 5 6 Number of carbon atoms Exam-style questions C2H5COOH H 29 H H H 6 H butane C 5 propene methane, ethane, propane, butane / CH4, C2H6, C3H8, C4H10 2 4 9 b 10 There is a steady increase in the boiling point of the alcohols with increasing chain length. Questions 1 8 butane Boiling point / °C 1 a H 3 B ; [1] [2] [1] Cambridge IGCSETM Chemistry – Harwood, Millington & Lodge © Cambridge University Press 2021 CAMBRIDGE IGCSE™ CHEMISTRY: COURSEBOOK Chapter 18 continued 4 a i H H H H C CC H HH HH H CC CC HC H HH HH HH HH H H H H H but-1-ene but-1-ene b butane and 2-methylpropane ; H HH HH H CH3CH(CHCH )CH CH(CH3)CH3 3 3 3 C CH CC CC HC C H H HH HH H butane H H H H butane H H H C HH HH C H H C CH CC HC C H H HH H H H 2-methylpropane 2-methylpropane [2 marks for names, 2 marks for displayed formulae] 30 [4] cyclobutane is not an alkene as it does not contain a carbon–carbon double bond ; [1] H H H but-2-ene but-2-ene CH3CH2CHCH CH3CH CH2CH3 2 3 2 H H H [2 marks for names, 2 marks for displayed formulae] ii H CH CC CC CC HC H [4] [1] c CnH2n + 2 ; d they contain the same functional group [1] and have similar chemical properties [1] ; / a consistent trend in certain physical properties with increasing chain length [1] ; Cambridge IGCSETM Chemistry – Harwood, Millington & Lodge © Cambridge University Press 2021 CAMBRIDGE IGCSE™ CHEMISTRY: COURSEBOOK Chapter 19 4 Science in context: Molecular envelopes 1 2 The fullerenes, despite the fact that they contain 60 or 70 carbon atoms per molecule, are considered to be simple molecular substances. The forces between these large simple molecules are relatively weak compared to covalent bonds. The nanotubes are enclosed cylinders that can contain the molecules of medicinal drugs – protecting the drug molecules from the environment as they move to the target organ. The nanotubes are stable, biocompatible polymers and can be tailored to form containers that package the drug and carry it across tissue barriers to the target site. The nanotubes have free electrons at their surfaces. The walls of the nanotubes can be modified to provided water-liking or membrane-liking surfaces to match the different environments in the body and the drug involved. H 5 2 3 Br C C H H H ethane → ethene + hydrogen 6 a propene + hydrogen → propane b C4H8 + H2O → C4H9OH 7 Ethanol is a renewable resource / can reduce dependence on petroleum imports / can reduce carbon monoxide emissions / can reduce environmental pollution, etc. 8 a yeast, carbohydrate source, water b carbon dioxide c H H H C C H H O H d oxidation a ethyl ethanoate b ethanol + ethanoic acid → ethyl ethanoate + water a propane + oxygen → carbon dioxide + water b C3H8 + 5O2 → 3CO2 + 4H2O a methane + oxygen → carbon monoxide + water Exam-style questions b CO 1 B ; c It binds to red blood cells (to the haemoglobin) and interferes with the transport of oxygen in the body. 2 a B ; [1] b C and D ; [2] c A ; [1] a a compound that contains carbon and hydrogen only ; [1] b no colour change as no reaction ; [1] c ethene and steam are compressed to 6000 kPa and passed over a phosphoric acid catalyst at 300 °C ; [2] d as a fuel and as a solvent ; [2] e (addition) polymerisation ; [1] a H b H c H H H C C C H H H H H Br C C C H H H 9 3 H H or H H Br H C C C H H H H The reaction requires light for it to take place. 4 31 Br C2H6 → C2H4 + H2 Questions 1 C2H4Br2 C ; [1] [1] Cambridge IGCSETM Chemistry – Harwood, Millington & Lodge © Cambridge University Press 2021 CAMBRIDGE IGCSE™ CHEMISTRY: COURSEBOOK Chapter 19 continued 5 a a substitution reaction ; [1] b 1,2-dibromoethane ; [1] c advantage: relatively cheap / materials are renewable [1] ; disadvantage: product needs further purification [1] ; d acidified potassium manganate(VII) [1] ; heat under reflux [1] ; e ethyl ethanoate ; H H H C C H H ethyl 32 H O C O C H H ethanoate [1 mark for name, 2 marks for displayed formula, both parts correct] [3] Cambridge IGCSETM Chemistry – Harwood, Millington & Lodge © Cambridge University Press 2021 CAMBRIDGE IGCSE™ CHEMISTRY: COURSEBOOK Chapter 20 b Science in context: Enzymes that recycle plastics 1 2 PET (a polyester) – the ester link Use of resources from the petrochemical industry / uncontrolled littering of the environment – land, rivers and oceans – dangers to wildlife / reliable and environmentally sensitive methods of disposal. Catalysts are reusable; enable reactions to take place under milder conditions than without; enzymes can be very specific and can be designed/modified to improve reaction conditions and specificity of product. O refinery gas, petrol (gasoline), naphtha, paraffin (kerosene), diesel, bitumen 2 road surfacing, ships’ engines, car engines, aircraft fuel (domestic heating) 9 Addition polymerisation takes place when many molecules of an unsaturated monomer (e.g. ethene) join together to form a long-chain polymer. n C C H 5 6 a a b H 33 a heat, catalyst H H C C H H n O C C O H H O O O O C C + H2O O the amide link (or peptide link) O O C C N N H H O O C C N N H H Proteins are made from 20 different amino acid monomers; nylon is made from just two monomers. 10 Simply burning plastic can produce toxic fumes such as hydrochloric acid from burning PVC / other toxic compounds can be formed (e.g. dioxins) / incineration at a precise temperature range can be used to destroy plastics. 11 Reuse means simply collecting the containers and then cleaning and reusing them for the same purpose / recycling involves shredding the original article and then making new and different items from the plastic. 12 Sorting the plastics into their different types / cleaning the plastic / some plastics are difficult to recycle because of the dyes that have been used to give them colour. H H Exam-style questions C C C 1 D ; CH3 H Cl 2 a A ; [1] b A ; [1] c C ; [1] H H C H b a carbon–carbon double bond H H H H H H C C C C C C C6H5 H 7 a c C10H22 → C8H18 + C2H4 high pressure O C decane → octane + ethene H H O Catalytic cracking is the thermal decomposition of a long-chain alkane to a shorter-chain alkane and an alkene (or an alkene and hydrogen). H + O H b 1 4 O 8 Questions 3 nylon – the amide link (or peptide link) C6H5 H [1] C6H5 H The monomers join together by a reaction in which a small molecule (usually water) is eliminated each time a link is made. Cambridge IGCSETM Chemistry – Harwood, Millington & Lodge © Cambridge University Press 2021 CAMBRIDGE IGCSE™ CHEMISTRY: COURSEBOOK Chapter 20 continued 3 4 a alkanes ; [1] b different boiling points ; [1] c airplane fuel / heating systems ; [1] d i heat / catalyst ; [2] ii hydrogen ; [1] e C10H22 → C4H8 + 2C3H6 + H2 ; a can be broken down into harmless substances [1] ; by bacteria / fungi naturally [1] ; b they are buried underground / used as landfill ; c they can harm sea life [1] ; / be consumed by sea creatures and enter the food chain [1] ; d they produce toxic gases when they burn ; 5 C ; 6 a b 34 [2] [1] [1] [1] i water ; [1] ii condensation polymerisation ; [1] i proteins ; [1] ii they are made by biological cells ; [1] Cambridge IGCSETM Chemistry – Harwood, Millington & Lodge © Cambridge University Press 2021 CAMBRIDGE IGCSE™ CHEMISTRY: COURSEBOOK Chapter 21 Science in context: Safe drinking water for all Experimental skills 21.1 1 Residue 1 Portable distillation units. Strengths: Provide access to distilled water in remote areas without need for large/expensive equipment / May be powered by renewable sources. Weaknesses: If using solar power, the unit will only operate under certain conditions / Produce limited amounts of clean water / May be limited access to replacement parts if there is a failure / Would need to be very robust if used in the field / May require training in safe use / Could be expensive. 2 It will enable the material to dissolve more quickly. 3 Salt is ionic and dissolves well in water. If the solution is concentrated by heat then the excess solid can be crystallised out. This would not be a good method for producing iodine crystals for several reasons. Iodine is toxic and unlike sodium chloride it has covalent rather than ionic bonding. Iodine is only partially soluble in water. Desalination units. Strengths: Provide access to drinking water in areas with access to seawater but limited freshwater / Can be run continuously / Proven technology. Weaknesses: May be limited access to parts if there is a failure / The waste product can be toxic to marine and coastal ecosystems / Energy intensive as require high temperature and pressure / Require training / Could be expensive. Experimental skills 21.2 2 Boiling points. 2 100 °C 3 Distillation involves heating the liquid so that components start to evaporate. As they evaporate, they travel up through the apparatus and into the condenser. In the condenser the temperature is lower and so the gas will condense. Different fractions will separate at different temperatures due to differences in their boiling points. The filter straw needs to remove particles of sand / silt / mud and harmful microbes such as bacteria that can cause disease. Questions Questions 1 The temperature should be recorded either with a thermometer or a digital temperature probe and meter. The volumes could be measured with a measuring cylinder or for greater accuracy a fixed volume could be measured using a volumetric pipette and a variable volume by use of the burette. 4 If there are two or more dots in a vertical line then the substance is a mixture. 5 A substance that remains on the baseline is insoluble in the solvent used. To improve the experiment the student needs to use an alternative solvent, e.g. swapping from water to ethanol. The teacher was not correct. The data has a narrow spread of results and so is precise; however, it is not accurate as the average of these results is not very close to the true value. 6 Rf = 2.3/2.8 = 0.82 (to 2 d.p.) 2 3 35 1 Error in the mass is 0.1/1.3 × 100% = 7.7%. Error in volume is 0.5/10.0 × 100% = 5.0%. The largest error is in the mass. Random errors could be reduced by repeating the experiment several times, checking for and removing anomalies and then calculating a mean average. Rf = distance moved by sample/distance moved by solvent front Distance moved by sample = Rf × distance moved by solvent front Distance moved by sample = 0.82 × 9.7 = 8.0 cm. Cambridge IGCSETM Chemistry – Harwood, Millington & Lodge © Cambridge University Press 2021 CAMBRIDGE IGCSE™ CHEMISTRY: COURSEBOOK Chapter 21 continued Processes for method 2: Experimental skills 21.3 1 Step a: The baseline needs to be drawn in pencil, not pen, as the pen could be soluble. Step c: The solvent should fall between the bottom of the paper and the baseline; it must not cover the base line as the samples will dissolve into the solvent and not travel up through the paper. Step d: The solvent should not travel all the way up but must be stopped just before it gets to the top of the paper. If this is not done then samples will continue to travel up the paper. 2 4 heat crushed powder ; • forms copper oxide ; • heat with charcoal ; • wash with dilute acid ; • filter and dry ; a to be able to measure the volume of the gas ; [1] not sufficiently accurate / can only measure to nearest cm3 ; [1] open the air hole at the base of the chimney fully ; [1] it is fractional distillation / to know when to change collecting vessel ; [1] b To reduce the amount of solvent lost through evaporation. c d Exam-style questions [1] [Max. 6 marks] 1 C ; 2 a tripod [1] ; and evaporating dish/ basin [1] ; the arrow also suggests a Bunsen burner [1] ; b A, C, F, D, B, E ; c blue ; [1] • draw a pencil line on the paper ; d because copper oxide reacts with acid ; [1] • spot some of the solution on the line ; [Each of the following scores 1 mark] • place in the solvent (water) ; Common starting process: • leave until the solvent front reaches a fixed point ; • se a locating agent to make the amino u acids visible ; • easure distance moved by the m different components ; 3 • crush lump of malachite ; • with a pestle and mortar ; e [Max. 2 marks] Processes in method 1: 36 • 5 when crystals form around the edge of the solution / when crystals form on a glass rod dipped in the solution ; [1] [Each of the following scores 1 mark] • dissolve in acid ; • named acid ; • calculate Rf values ; • filter ; • • electrolyse filtrate ; compare with reference values to identify ; [Max. 6 marks] • recover copper from cathode ; Cambridge IGCSETM Chemistry – Harwood, Millington & Lodge © Cambridge University Press 2021 CAMBRIDGE IGCSE™ CHEMISTRY: COURSEBOOK Chapter 22 light green flame would indicate the presence of barium ions. Barium sulfate is BaSO4. Getting started Criteria for a chemical test might include: It needs to give a clear result (e.g. a colour change) / It should be specific (i.e. works for only one chemical) / Ideally it should be quick and simple to use / Should not use hazardous chemicals Reactions students might have seen include: Standard tests for gases such as hydrogen, oxygen and carbon dioxide / Standard test for a double bond (bromine water) / Standard test for an acid (addition of a carbonate) / Possible tests for the presence of cations and anions These tests might be needed by: Companies monitoring the quality of air or water / Government bodies / Health and safety committees 3 Tap water can contain dissolved ions and may have given a false positive result, with the colour being from the impurities and not the sample. The experimental design can be improved by using distilled water. 4 C and E 5 The use of state symbols in C shows that this is a precipitation reaction. 6 AlCl3(aq) + 3NaOH(aq) → Al(OH)3(s) + 3NaCl(aq) Experimental skills 22.1 1 A precipitate is an insoluble compound produced during a precipitation reaction (the reaction that produces an insoluble salt when solutions of two soluble salts are mixed). 2 Iron(II) precipitates are green in colour; iron(III) precipitates are brown in colour. 3 Ammonia is a base. To ensure their conclusions were valid: To check results are repeatable / To sample multiple times Science in context: Bottled water – finding a solution to what ions it contains 1 2 Mineral water might be thought of as pure because it has had no other chemicals added to it and it has come from a natural source. Chemically, mineral water is not pure. It is a mixture, because it contains dissolved impurities. Questions 7 Iron(II) chloride would initially produce a green precipitate. Iron(III) chloride would produce a brown precipitate. One problem is to ensure that the water does not contain harmful microbes (these would normally be removed by disinfection using chlorine). Another problem is the potential for changes in composition that may result from seasonal weather variations. 8 When sodium hydroxide solution is added to copper(II) sulfate solution, a light blue precipitate is formed. When dilute ammonia solution is added to copper(II) sulfate solution, initially a light blue precipitate is formed but as more ammonia solution is added this dissolves and produces a dark blue solution. 9 A green precipitate could indicate the presence of either iron(II) or chromium(III) ions and so their conclusion was not valid. To produce a valid result, the test should be repeated using excess sodium hydroxide. If a green precipitate forms but then redissolves, the sample contains chromium(III). Questions 37 1 The nichrome wire probe is cleaned by placing it alternately in a roaring flame and concentrated acid. Once clean it can be dipped in the acid and then into the sample containing the sodium ions. A positive test for sodium ions will be the production of a yellow flame. 2 The lilac flame would indicate the presence of potassium ions. Potassium sulfate is K2SO4. The red flame would indicate the presence of lithium ions. Lithium sulfate is Li2SO4. The Cambridge IGCSETM Chemistry – Harwood, Millington & Lodge © Cambridge University Press 2021 CAMBRIDGE IGCSE™ CHEMISTRY: COURSEBOOK Chapter 22 continued 10 Student A’s results would be valid as the calcium ions would produce an orange-red flame; no detectable flame colour would be seen with the zinc or aluminium ions. Student B’s results would not be valid as both zinc or aluminium precipitates redissolve in excess sodium hydroxide. To produce a valid conclusion student B would need to repeat the experiment using dilute ammonia solution. Under these conditions the precipitate containing zinc ions would redissolve but not that containing either calcium or aluminium. 18 The pieces of glassware are a volumetric pipette that adds an accurate, fixed volume of liquid and a burette, which adds an accurate but variable volume of liquid. 11 In general, the reaction of a carbonate with any acid produces carbon dioxide. Sodium carbonate solution reacts with acids as follows: Sodium + sulfuric → sodium + carbon + water carbonate acid sulfate dioxide 21 The mean titre would only use the results within 0.10 cm3: i.e. mean titre = (12.15 cm3 + 12.10 cm3 + 12.10 cm3)/3 = 12.12 cm3. Na2CO3(aq) + H2SO4 (aq) → Na2SO4 (aq) + CO2(aq) + H2O(l) Sodium + nitric → sodium + carbon + water carbonate acid nitrate dioxide Na2CO3(aq) + 2HNO3 (aq) → 2NaNO3 (aq) + CO2(g) + H2O(l) 12 Acidified silver nitrate would produce a yellow precipitate with the magnesium iodide and a white precipitate with the magnesium chloride. 19 Methyl orange and thymolphthalein both produce clear colour changes at the end-point, universal indicator does not. 20 Swirling ensures everything is mixed and also ensures liquid that might have splashed onto the sides of the flask is returned to the reaction. Exam-style questions 1 D; 2 a b c 3 [1] To separate the two components of the mixture. ; i aluminium [1] ; sulfate [1] ; ii calcium [1] ; carbonate [1] ; 13 This would negate the results as the sulfuric acid introduces sulfate ions and so a white precipitate of barium sulfate is immediately produced. 14 Al → Al3+ + 3e− 15 a b adding acidified silver nitrate salt flame test slowly adding excess aqueous sodium hydroxide potassium sulfate lilac colour no reaction no reaction barium bromide green colour no reaction cream precipitate lithium iodide red colour no reaction yellow precipitate chromium(III) no colour green white chloride produced precipitate, precipitate redissolves Carbon dioxide was present. Ca(OH)2(aq) + CO2(g) → CaCO3(s) + H2O(l) [1] aluminium sulfate ; MgI2(aq) + 2AgNO3(aq) → Mg(NO3)2(aq) + 2AgI(s) MgCl2(aq) + 2AgNO3(aq) → Mg(NO3)2(aq) + 2AgCl(s) [1] [1 mark for each answer, Max. 6 marks] 16 The gas is not carbon dioxide and it is not oxygen. 17 a b 38 Purple manganate(VII) ions are reduced to very pale pink manganese(II) ions. The sulfur is oxidised and the manganese is reduced. Cambridge IGCSETM Chemistry – Harwood, Millington & Lodge © Cambridge University Press 2021 CAMBRIDGE IGCSE™ CHEMISTRY: COURSEBOOK Chapter 22 continued 4 a i add aqueous sodium hydroxide slowly until in excess [1] ; green precipitate which does not redissolve [1] ; ii add acidified barium nitrate [1] ; white precipitate [1] ; These two tests can be given in either order. b i pass gas through lime water [1] ; lime water turns milky [1] ; ii add acidified potassium manganate(VII) [1] ; turns colourless [1] ; These two tests can be given in either order. 5 39 [Each of the following scores 1 mark] • a dd named volume of first vinegar to a flask ; • add a named indicator ; • slowly add from a burette ; • named alkali ; • note volume needed for neutralisation ; • repeat with same volume of second vinegar ; • largest volume used (titre) = most acid. ; [Max. 6 marks] Cambridge IGCSETM Chemistry – Harwood, Millington & Lodge © Cambridge University Press 2021