Lots of types were used at the London 2012 Olympics Scenario - Howard was in charge of designing a new toy car for an infant (3-6 years old.) He had the choice of using metal, wood or plastic in his design. Howard decided to use plastic. Why? Properties of Plastics (Polymers) • Plastics are used for so many jobs because they have many useful properties. Properties of materials describe what they are like and how they behave. • For example, a plastic shampoo bottle has the following properties; 1. Flexible – the shampoo can be squeezed out of the bottle. 2. Watertight – the shampoo will not leak. 3. Shatterproof – the bottle will not break if dropped. 4. Light – this also make it cheaper to transport. • Plastics are good heat insulators – this means plastic doesn’t let heat escape. Plastics are also good electrical insulators • Plastics can be coloured (any colour) at the manufacture stage unlike metal and wood. Hydrogels • Hydrogels are smart materials. • Hydrogels can change structure in their environment. response to • Hydrogels are used in nappies and contact lenses (amongst other things) Kevlar • Kevlar is an incredibly strong yet lightweight fibre. • Kevlar is strong because of its bonding. (higher) • Kevlar is used in a range of things including stab vests, motorcycle equipment and now even football boots. Water Soluble Polymers • Water soluble polymers are plastics that dissolve in water. • In the past high temperatures were needed to dissolve the polymer but advances in recent years means lower temperatures are successful too. • Water soluble polymers are used in hospital laundry bags and washing up ‘liquitabs’ ‘Special’ Polymer Name ‘Special’ Property ‘Kevlar’ Bulletproof (very strong yet lightweight) ‘Biopol’ Biodegradable plastic (breakdowns down naturally) Poly(ethenol) Soluble in water (i.e. it dissolves in water) Hydrogels can change its structure in response to salt concentration, pH and temperature. Advantages and Disadvantages of Plastics The main advantage plastics is also the reason why plastic is such a problem. It lasts forever. (doesn’t biodegrade) Burning plastics can be very dangerous as they give off toxic and poisonous fumes. Plastics are reusable. Different plastics give off different types of fumes. All plastics give off carbon monoxide. Plastics are usually shatterproof and are see-through. Light-weight and odourless. Made from Crude Oil which is a finite resource. (i.e. it’s running out) Plastics don’t biodegrade (i.e. they don’t break down naturally) Reminder; An addition reaction occurs when something adds across a double bond. During an addition reaction the carbon to carbon double bond is broken. How are Addition Polymers are made? Plastics are made up of huge long chain molecules called polymers. Polymers are made when many small molecules, called monomers, join together. These monomers (usually alkenes) must contain a carbon double bond and join together to form saturated polymers. This process is called addition polymerisation (only carbons bonded together i.e. carbon ‘backbone’) Making poly(ethene) (mono means one, poly means many) Monomer name; ethene Polymer name; poly(ethene) Monomer structure; Polymer structure; Repeating unit; Making poly(propene) Monomer name; propene Polymer name; poly(propene) Monomer structure; Polymer structure; Repeating unit; Making poly(styrene) Monomer name; Monomer structure; Polymer structure; Repeating unit; Polymer name; Reminder; In a condensation reaction two molecules join and a small molecule (often water) is removed. Making an ester is an example of a condensation reaction. How are Condensation Polymers are made? Some examples of condensation polymers are nylon, poly(ester), proteins, starch and cellulose. Poly(ester) and nylon are synthetic (man-made) while the others mentioned above are natural. The monomers used to make condensation polymers have two functional groups at each end of the molecule – they are bifunctional. A small molecule is also produced when a condensation polymer is formed. This process is called condensation polymerisation (other elements as well as carbon are bonded together in the molecule’s ‘backbone’) Making a poly(ester) Carboxylic acid + Alcohol Ester + Water Therefore; ‘Diacid’ + ‘Diol’ Monomer structures – Polymer structure – Poly(ester) + Water Making Starch Starch is a natural condensation polymer made when many glucose monomers join together. Starch, like other natural polymers, are biogradeable (break down/decompose naturally) Monomer structure (glucose) – Polymer structure – Metallic Bonding • Metallic bonding – unsurprisingly – only appears in metal elements. • Metallic bonding occurs between metal ions (positively charged) and delocalised outer shell electrons (negative) – opposite attract. • ‘delocalised’ means the electrons are common to all of the ions (not just one atom i.e. they hop from one to another) The main properties of metals • Strength – metals that are strong are used to make car bodies, bike frames, ships hulls etc. • Malleability (mouldable) – this means that they can be shaped by hammering or rolling and can be bent without breaking. For example car chassis. • Conduction of electricity – all metal elements conduct electricity. Non metals (except carbon in graphite form) do not. Copper is used in household wires, aluminium wires are used in overhead power lines. • Conduction of heat – metals are good conductors of heat. We use metals like aluminium, iron and copper for cooking pots and pans. • Density – If we had two pieces of metals the same size, the higher density metal will be heavier than the lower density one. e.g. Lead is highly dense and was useful in old divers suits (i.e. they’d sink!) Aluminium less dense and is used to make planes. Alloys • The properties of metals can be changed and improved by making alloys. (i.e. make it stronger or shine more etc. • An alloy is a mixture of two or more metals. (in some cases some non-metals are also added) • The usual way to make an alloy is to melt together the elements that make it up. • Bronze, brass and stainless steel are examples of common everyday alloys. Lithium Potassium Calcium Sodium Magnesium Aluminium Zinc Iron Nickel Tin Lead Copper Silver Mercury Gold Ores Unreactive metals such as silver and gold are found uncombined – this is why ‘panning for gold’ can happen. In nature most metals are found in compounds – these compounds are known as ores. Metals can be extracted from their ores in a variety of ways. 1. Extraction with heat only – gold, silver and mercury. 2. Extraction with heat + carbon 3. Extraction with electricity Extraction: Heating with Carbon Some metal ores have to be heated with carbon. This is because the metal ore (usually a metal oxide) needs the carbon to be able to pull the oxygen away from the metal. This leaves the pure uncombined metal. Carbon dioxide is formed too. METAL OXIDE + CARBON METAL + CARBON DIOXIDE Iron and the Blast Furnace Stage 3 2 1 Extraction of Metals using electricity More reactive metals (Al and above) are too volatile and therefore dangerous to extract via heat + carbon. positive metal Instead we use electricity to attract the ______ negative electrode. ion to the _________ Metals and Oxygen Metal + Oxygen Metal oxide For example; Magnesium + Oxygen Magnesium Oxide All of the metals above __________ in the reactivity series react with oxygen. Metals and Water Metal + Water Metal Hydroxide + Hydrogen Example; Potassium + Water Potassium Hydrogen Hydroxide + __________ ____________ Formula equation: All of the metals above __________ in the reactivity series react with water. (hint - every metal with m at end !!) Metals and Acid Metal + Acid Example; Zinc + Hydrochloric Acid Salt + Hydrogen Zinc Hydrogen Chloride + _________ _________ Formula equation: All of the metals above _________ in the reactivity series react with acid. The Reactivity Series • A reactivity series of metals is a ‘league table’ which puts the metals in order of how reactive they are. • The reactivity series is also known as the electrochemical series. • The most reactive metals are at the top and the least reactive are at the bottom. Electrolysis Electrolysis is the splitting (lysis) up of a compound using electricity (electro). Oxidation and Reduction Copper Chloride Example Word bank; atoms, copper, gain, electrons, ions, lose, solution, negative, positive ions (in solution) lose electrons forming The chlorine ______ atoms We see these as gas at the ________ positive chlorine _______. electrode. gain electrons forming The copper ions (in solution) ______ negative copper atoms. We see these as solid at the _______ electrode. 2Cl- Cl2 + 2e- and Cu2+ + 2e- These are called ion-electron equations. Cu OILRIG Oxidation Reduction Is Is Loss Gain (of electrons) (of electrons) In the copper chloride example; Reduction = Oxidation = Ion electron equations are found in the data booklet where they are written as reduction reactions. Reducing agents help reduction to occur by providing electrons. Electrochemical Series Metals _______ lose electrons to obtain a full outer electron shell. This makes the metal stable. The electrochemical series is a list of metals arranged in rank order of how easily the metal atoms lose electrons. The electrochemical series in your data booklet Experiment – Measuring a voltage between two metals. Voltmeter / other metals A cell can be made when two different metals are connected in contact with an electrolyte. In this cell the electrolyte is sodium chloride. An electrolyte is always an ionic compound and it completes the circuit as it allows the ions flow. When metals ________ their electrons, they lose do so with a certain force. This force is known as voltage. When two different metals are connected together in a cell (a battery), the metal with the higher force pushes its electrons on to the other metal. (‘bully rule’) No voltage is obtained when the same metal is connected together. i.e. two pieces of copper metal. Important The further apart the metals are in the electrochemical series, the higher the voltage. Electrons flow along the wire from the metal higher in the electrochemical series to the metal lower down. In which direction will electrons flow in the following? • A magnesium/iron cell? wires _____ to _____ through the _____. • A silver/aluminium cell? _____ to _____ through the _____. wires • A Cu/Sn cell? _____ to _____ through the _____. wires Combining Batteries, Oxidation and Reduction Remember the metal higher up in the electrochemical series loses its electrons more easily – i.e. oxidation. Write the ion electron equations and label them reduction / oxidation for the following batteries; • • • • Tin Silver Cell Magnesium Zinc Cell Sodium Gold Cell Lead Iodide Cell REDOX Reactions Oxidation cannot happened without reduction and vice versa. Therefore reactions in electric cells (batteries) can be described as REDOX. Rechargeable batteries and fuel cells are technologies which use REDOX reactions. Writing REDOX equations Zinc Copper Cell OXidation – REDuction – REDOX equation i.e. the oxidation and reduction equations have been combined and the electrons have been cancelled. Potassium Iodine Cell Oxidation – Reduction – Redox Equation - If the number of the electrons is NOT the same on each side of the equation then you need to multiply the equations to find a common factor. Examples Write the REDOX equations for the following; (show all working please) Magnesium Tin Cell Gold Zinc Cell Lithium Aluminium Cell Copper Silver Cell Calcium Bromide Cell Nickel Chloride Cell Iron (III) Tin Cell Aluminium Copper Mercury Silver Cell Sodium Lead Cell • To grow well, plants require some essential elements. These are called NUTRIENTS. • Nutrients are made from water soluble compounds. • The most important nutrients that plants require are Nitrogen, Phosphorus and Potassium (often referred to as NPK) • These nutrients are often added in the form of FERTILISERS Name + Chemical Formulae of Fertilisers • Ammonium Nitrate (NH4+)(NO3-) • Ammonium Phosphate (NH4+)3(PO43-) • Potassium Nitrate K(NO3-) • Potassium Phosphate K3(PO43-) i.e. compounds that contain potassium, phosphorus and/or nitrogen Problems with fertilisers • Many fertilisers are very soluble, sometimes too soluble. • If it rains, fertilisers are carried off of the land into streams, rivers and lochs. • In lochs, high nitrate (NO3-) levels encourage algae growth. • The algae decrease the amount of oxygen dissolved in the water thus killing fish and other marine life. • High nitrate levels in drinking water make it unfit for human consumption. Nitrogen Fixation and the Nitrogen Cycle • Some plants can absorb nitrogen directly from the air. e.g. peas, beans and clover. (leguminous plants) • Leguminous plants have nodules which contain nitrifying bacteria. • Most plants can’t do this and require to absorb nitrogen in the form of nitrogen compounds. The Haber Process The Haber Process is the industrial method used to make ammonia. N2(g) + 3H2(g) 2NH3(g) (this is a reversible reaction) • Ammonia is used in the manufacture of nitric acid. • An iron catalyst, a high temperature (500oC) and high pressure (about 150-300atms) are used to increase the reaction rate. • Nitrogen is obtained by the distillation of air and hydrogen is obtained from methane (natural gas) The Ostwald Process The Ostwald Process is the industrial method used to make Nitric Acid. (HNO3) NH3(g) + O2(g) NO(g) + O2(g) NO2(g) + H2O(l) NO(g) + H20 NO2(g) HNO3(aq) + NO(g) • A platinum catalyst and a high temperature 9000C are required to make the first stage happen. • Nitric acid is used in the manufacture of fertilisers, explosives and plastics. • The reaction is exothermic which means it only has to be heated once as it keeps itself going. Percentage Composition The percentage composition allows us to calculate the percentage of each element in a compound. Percentage composition is also known as ‘percentage by mass’. Percentage of element in a compound Mass of Element (in Compound) x100 Total mass of Compound Worked Example Calculate the percentage by mass of oxygen in aluminium oxide (Al2O3). Formula mass (total mass) of Al2O3 ; Percentage of oxygen in Al2O3; Worked Example 2 Calculate the percentage by mass of nitrogen in ammonium nitrate (NH4NO3). Formula mass (total mass) of NH4NO3 ; Percentage of nitrogen in NH4NO3; Examples 1) Calculate 2) Calculate 3) Calculate 4) Calculate 5) Calculate 6) Calculate 7) Calculate 8) Calculate 9) Calculate 10) Calculate 11) Calculate 12) Calculate % % % % % % % % % % % % of of of of of of of of of of of of iron in Fe2O3 sulphur in SO2 lithium in LiOH oxygen in LiOH hydrogen in LiOH oxygen in H2SO4 nitrogen in HNO3 sulphur in magnesium sulphite sodium in sodium sulphate aluminium in aluminium nitrate. carbon in hydrogen carbonate zinc in zinc (III) ethanoate Particle Proton Mass 1 Charge +ve Location Nucleus Neutron Electron 1 0 0 -ve Nucleus Electron shells 16 8 Isotopes are atoms of the same element (same number of protons) but have different number of neutrons. This means for isotopes, the atomic number stays the same but the mass number changes. Many elements exist as 2 or more isotopes. Isotopes 28 14 Si 25 14 Si 31 14 Si 27 14 Si Protons Electrons Neutrons Radioactivity Radioactivity results from unstable isotopes of elements spontaneously decaying with the emission of radiation. This makes the isotopes become more stable. Isotopes that emit radiation are known as radioisotopes. What makes a nucleus unstable? Protons are positively charged and it is thought that the neutrons prevent the protons repelling each other. If an atom has too many or too few neutrons for the number of protons, the atom will be unstable and therefore, radioactive. Very large atoms (atomic number > 83) are always unstable. Types of Radiation There are three types of radiation; 1) Alpha (α) 2) Beta (β) 3) Gamma (γ) Alpha and beta are made up of particles; Gamma radiation is made of waves and has no mass. Alpha Radiation The particles that make up alpha radiation are helium nuclei (i.e. 42He) Alpha decay Example i.e. when a nucleus emits an alpha particle its atomic number will decrease by two and its mass will fall by 4. Beta Radiation The particles that make up beta radiation are electrons (i.e.0-1e) Beta particles are formed when neutrons break up into protons and electrons. Beta decay Example i.e. The atomic number increases by 1 but the mass number will remain unaffected. Gamma Radiation Since gamma rays have no mass and no charge, their emission has no effect on the mass number or the atomic number of the radioisotope. The atom does however lose energy. Artificial Radioisotopes For nuclear reactions to occur, the bombarding particles must have a high energy to overcome the forces of repulsion from the nuclei. Example 1 – Cobalt 60 - Neutron Capture Cobalt 60 is used in cancer therapy and is made in nuclear reactors where a target of stable cobalt 59 molecules are bombarded by neutrons. Example 2 – Nitrogen 14 - Proton Capture When nitrogen 14 is bombarded with protons the following reaction could happen. Half Life Radioactive decay happens at random. However over time this ‘averages out’ and a value can be calculated – half life. Half life is the time required for something to fall to half its initial value (in particular, the time for half the atoms in a radioactive substance to decay) Half life Calculation Example 1 A sample of a radioisotope has a half life of 14 days. After 56days what mass of the original 80g sample remained? Half life Calculation Example 2 A radioisotope of carbon had an initial radiation reading of 200 counts per minute. 24 days later the reading was found to be 50 counts per minute. How many half lives occurred in 24days. Half life Calculation Example 3 A radioisotope has a half life of 700 years. How long will it take for 96g of a sample to decay to 12g?