❖ State why two isotopes of have the same chemical properties same number of electrons same number of outer shell electrons. ❖ Explain why increasing the temperature increases the rate of reaction. particles move faster and have more energy more collisions per second so greater collision rate. frequency of collision increase more of the (colliding) molecules / particles have sufficient energy (activation energy) to react / more of the collisions have sufficient energy (activation energy) to react ❖ Explain why decreasing the temperature decrease the rate of reaction. particles have less energy and move slower. fewer collisions per second so smaller rate of collision. frequency of collisions decrease. fewer portion of particles have sufficient energy to react. fewer portion of particles have energy greater than equal to activation energy. Give two properties of aluminium that make it suitable for use in overhead electricity cables. ductile / malleable 1 conducts (electricity) low density protective oxide layer What is a saturated solution? a solution that can dissolve no more solute at the particular/specific/any given temperature Why temperature doesn’t increase at boiling or melting? energy is used to break bonds / overcome attraction between molecules Why is cotton wool used in this experiment? to allow gas to escape. to prevent loss of acid. Why does the graph levels off in this experiment? reaction finished all the reactant is used up. Describe the structure and bonding of metals (lattice of) positive ions / cations (delocalised / sea of) electrons attraction / attract between positive and negative Why an atom has overall charge 0? Same number of protons and electrons Why an ions has a charge of X+? X more protons than electrons Why an ions has a charge of X-? 2 X less protons than electrons Why using lumps of solids decreases rate of reaction? (lumps have) smaller surface area OR powder has larger surface area (lumps have) fewer collisions per unit time / less collision frequency OR powder has more collisions per unit time / more collision frequency What is the observation when sodium or any metal react with water? fizz / bubbles moves floats melts / forms a ball gets smaller / disappears Why do gases diffuse? due to random motion of molecules / particles from the region of higher concentration to lower concentration. Which element is found in clean dry air? Argon Which compound is found in clean dry air? Carbon dioxide Why a solid is added in excess to a acid? to make sure all the acid reacts If excess calcium metal is added to dilute hydrochloric acid instead of excess zinc powder, pure calcium chloride crystals do not form. Explain why Ca will also react with water Describe how to check if all the water has been given off from a hydrated salt? heat again and weigh again and repeat until mass is constant Why a reaction is exothermic? Chemistry past paper Common Questions By Vasumitra Gajbhiye 3 more energy released (in bond formation) than used/taken in (in bond breaking) Which process is used to separate the products of hydrolysis of long chain protein. Chromatography. Describe how oxides of nitrogen form in a car engine. nitrogen and oxygen (from the air) react (in the engine) (due to) high temperatures Which catalyst is used in catalytic converter? Platinum / Rohidum What is catalyst? (a substance which) increases the rate of a reaction remains unchanged/ unaffected/ unused or without changing mass Explain, in terms of particles, why does the rate of reaction decrease as the time increase? • concentration of particles decreases • lower rate of collisions of particles What are the effects of nitrogen dioxide? • Respiratory problems • Acid rain What is meant by the term redox? reduction and oxidation occurs simultaneously. Describe how solid sodium conducts electricity. electrons move/mobile/flow 4 Explain why sodium chloride conducts electricity when molten. Ions move/are mobile/flow What happen to rate of reaction when surface area is increased? Rate of reaction increase. More collisions per unit time. When group 1 element react with cold water what is formed? metal hydroxide Why a substance is oxidising agent? It has gain electrons hence reduced. Why a substance is reducing agent? It has lost electrons hence oxidised. What is the colour of bromine? Orange – Brown liquid State a pH number that indicates the presence of a strong alkali. 14 State how the energy profile diagram shows this is an exothermic reaction. energy of products is lower than energy of reactants 5 Describe metallic bonding. Lattice of (named) metal ions in sea of delocalised electrons attraction between positive (named metal) ions and negative electrons Explain why nitrogen does not conduct electricity. No mobile electrons OR no ions Explain, in terms of attractive forces between particles, why nitrogen has a low melting point. Weak forces of attraction between molecules Why ionic compound don’t conduct electricity when solid but conduct when molten? Explain in terms of structure and bonding. ions (ions) are fixed (in a lattice) ions are mobile Explain why molten ionic compounds can conduct electricity. ions can move through the structure Describe what can be done to any ionic compound to allow it to conduct electricity. dissolve it in water Explain, in terms of attractive forces between particles, why (any covalent compound) has a low melting point. forces of attraction between molecules AND are weak / need a small amount of energy to break 6 Why ionic compounds have high melting point? strong forces of attraction (between oppositely charged ions) Explain why covalent compounds are non-conductors of electricity? no moving or flowing or mobile charged particles or ions or electrons Which type of bond is present in carbon dioxide? Double covalent bond. What is ionic bond? oppositely charged ions (ions) are attracted Give physical properties of ionic compounds. physical constants: high boiling point / melting point conductivity: conduct (electricity) when aqueous or conduct (electricity) when molten solubility: soluble in water Explain, in terms of particles, why brass is harder than pure zinc. exists as layers (alloy) contains different sized (copper) atoms makes it more difficult for layers (of atoms) to slide over each slip/shift other State the term used to describe the structure of diamond. Giant covalent CONTACT PROCESS What are the steps in contact process stage 1 Molten sulfur is burned in air to produce sulfur dioxide gas. stage 2 Sulfur dioxide is reacted with oxygen to form sulfur trioxide. stage 3 Sulfur trioxide is combined with concentrated sulfuric acid to form 7 oleum, H2S2O7. stage 4 Oleum is added to water to form sulfuric acid CRYSTALLISATION Why is the residue rinsed after filtration? To make sure all the filtrate goes through. no filtrate left behind in the filter paper. (This will increase yield). To wash-out / dissolve / remove salt How to obtain pure crystals from a filtrate? evaporation the starting of crystallisation drying the crystals Why the mass of crystals obtained was less than theoretical mass? some salt remains in solution / some salts does not form crystals OR some of the crystals decomposed OR some crystals lost in transfer State two observations that would indicate that some salts are in excess in step 1. no more bubbling / fizzing / effervescence solid or powder stops dissolving/ solid remains. What evidence would show that the solution was saturated? when crystals form on a glass rod withdrawn from solution / on a sample of solution placed on microscope slide etc. Why should the aqueous saturated salt not be heated to dryness? (heating to dryness) would remove water of crystallisation to form anhydrous powder. Suggest why more crystals of magnesium sulfate appear on cooling. 8 solubility (of MgSO4 / solid) decreases (as temperature decreases) ELECTROLYSIS State what is meant by the term electrolysis breakdown by (the passage of) electricity of an ionic compound in molten or aqueous (state) State and explain what would happen to the mass of the negative electrode during the electrolysis of concentrated copper(II) chloride. increases (solid) copper deposited What happens to the colour of solution during electrolysis of coloured compound? colour fades / becomes pale(r) / becomes colourless / becomes lighter named anions (ions) removed (from solution) Give one reason why metal spoons are electroplated with silver. Improves appearance prevent / resist corrosion / oxidation antibacterial When a gas is formed what is observed? fizzing/ bubbles/ effervescence Explain why the ionic compound needs to be aqueous or molten. So that ions are mobile and can move Explain why inert electrodes are used. they do not react EQUILIBRIUM 9 State features of equilibrium. reaction is reversible rate of forward reaction = rate of reverse reaction. concentrations of reactants and products are constant Explain, in terms of particles, why a high temperature increases the rate of reaction. particles have more energy (E) rate of collisions increase/ more collisions per unit time(per second) a higher proportion of particles have energy greater than activation energy (E > EA) If forward reaction is exothermic what happens to the amount of product when temperature is increased? less amount of product equilibrium moves left and because forward reaction is exothermic If a product is removed from the RHS what happens to the mass of other product? more product equilibrium moves right to replace (named product which is removed, e.g. water) If the pressure is increased, the yield of ammonia increases. Explain why, in terms of equilibrium. equilibrium shifts / moves in forwards direction fewer molecules / moles (of gas) on RHS Suggest why the position of equilibrium does not change. same number of gas moles on both sides of the equilibrium / same number of gas molecules on both sides of the equilibrium ETHANOIC ACID MAKING 10 Ethanol will react with hot aqueous potassium manganate(VII) to form ethanoic acid. State the other condition needed for this reaction to take place. presence of an acid ETHANOL MAKING How ethanol can be made by fermentation. C6H12O6 → 2CO2 + 2C2 H5 OH anaerobic respiration of yeast at 37°C using aqueous glucose What type of reaction is it when ethene is converted to ethanol? Addition of steam What are the reagents and conditions required for conversion of ethene to ethanol? stem catalyst pressure temperature What are the two products of fermentation? Carbon dioxide and ethanol EXTRACTION Give two reasons for using coke in the blast furnace. (coke) releases heat (when it reacts with oxygen or reacts in air) OR (acts as a) fuel 11 OR increases temperature (in the furnace) / heats (the furnace) OR source of energy (coke or carbon monoxide) reduces iron oxide OR is a reducing agent OR converts iron oxide to iron / removes oxygen from iron oxide (coke) reacts with oxygen to form carbon monoxide OR reacts with carbon dioxide to form carbon monoxide Name two waste gases that leave the blast furnace during extraction of iron. Nitrogen Carbon dioxide Suggest one benefit to the environment of reducing the operating temperature of electrolysis of aluminium oxide. less co2 emission Explain why the anodes need frequent replacement. anodes or carbon / graphite react with oxygen / O2 (form) carbon dioxide HARBER PROCESS State one source of hydrogen for manufacture of ammonia. Methane Explain why a lower temperature and a higher pressure are not used. Lower temperature → rate of reaction slower Higher pressure → expensive/ specialised equipment 12 ORGANIC CHEMISTRY What is meant by unsaturated? not all c-c bonds are single. contain at least one c=c bond. What are the reagents and conditions required for conversion of a alkene to alkane? hydrogen catalyst high temperature. State what is meant by the term functional group. the atoms / group of atoms which give (any molecule its) chemical properties If the number of carbon in the chain increase what happen to it’s boiling point? boiling point increase State are general characteristics of a homologous series. same or similar chemical properties or reactions same general formula consecutive members differ by CH2 13 same functional group common (allow similar) methods of preparation physical properties vary in predictable manner / show trends / gradually change OR example of a physical property variation i.e. melting point / boiling point / volatility Which process is used to make alkenes? Cracking Iron(II) sulfate can be converted to iron(III) sulfate by potassium manganate(VII) at room temperature. What condition must be used for this reaction to occur? presence of acid What happens to viscosity as we move up the fractionating column. it decrease What happens to flammability as we move up the fractionating column. it increase What difference in the molecules of gasoline and kerosene causes differences in viscosity and flammability? kerosene has molecules with a longer carbon chain POLYMERS How many molecules of water is formed when one ester link is formed? 1 14 Describe what is meant by the term addition reaction. (only) one product is formed. Give one condition needed when ethanoic acid reacts with the alcohol to make this ester. acid conc sulfuric acid / heat (catalyst) Name a polyester? Terylene/ PET PROTECTING IRON Explain how completely coating an iron object with a layer of zinc prevents rusting prevents water or / and oxygen reaching iron Rusting of iron ships can be prevented by attaching zinc blocks to the hull of the ship. Explain how this prevents rusting. zinc more reactive (than iron) 15 zinc corrodes / oxidises / reacts in preference to iron Explain how the magnesium blocks prevent iron from rusting magnesium is more reactive than iron / steel ORA (1) iron is not oxidised OR iron does not lose electrons OR magnesium loses electrons more easily than or in preference (to iron) ORA OR magnesium is oxidised more easily or reacts with oxygen more easily or corrodes more easily or in preference (to iron) SALT PREPARATION What is meant by the term precipitate? a solid which forms when two solutions are mixed / reacted / added What compounds can be used to make metal salts? Metal oxide, metal carbonate, metal hydroxide How precipitation is performed practically? (add) water (to both salts) dissolve both salts / make solutions filter (lead(II) iodide) wash (residue of lead(II) iodide) with water AND dry e.g. with filter paper / description of washing and drying How to make salt crystals from metal carbonate and acid? add metal carbonate to sulfuric acid until it stops dissolving or no more effervescence filter excess metal carbonate 16 evaporation of filtrate to form dry crystals State two observations when metal carbonate reacts with acid? fizzing / effervescence solid disappears / dissolves Name the experimental technique used when salts are made by reacting a dilute acid with an aqueous alkali. Titration TEST Test for oxygen. glowing splint relight Test for hydrogen. Burning splint squeaky pop Test for sulfur dioxide. acidified aqueous potassium manganate(VII) purple to colourless What is produced when iron(II) sulfate (or any other metal) react with ammonia? Iron (II) hydroxide is formed (or any other metal hydroxide is formed) 17 TRANSITION & GROUP 1 ELEMENTS What are the chemical properties of transition metals? act as catalyst variable oxidation states Coloured compounds What are the physical properties of transition metals? malleable good conductors of heat and electricity high melting point hard and strong/ tough high density What are the difference between physical properties of transition metals and group 1 elements. higher melting point high density hard What are the difference between chemical properties of transition metals and group 1 element. act as catalyst have variable oxidation states form coloured compounds What are the difference between physical properties of group 1 elements and transition metals. low melting point or low boiling point soft low density 18 State physical properties of Group I metals which are similar to those of transition metals. shiny / lustrous conduct electricity conduct heat ❖ ❖ ❖ ❖ POLYESTER 19 ❖ EQUAL 6 ❖ ❖ 20 and reactant conc decrease. Oxidation number \ 21 22 \ 23
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