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Paper 2 - AQA GCSE Chemistry
"Definition of a carbon footprint - CORRECT ANSWER The total greenhouse gases emitted over the full life cycle of a product, service or event." "Condensation polymerisation - CORRECT ANSWER Condensation polymerisation involves monomers with two functional groups. When these types of monomers react they join together, usually losing small molecules such as water, and so the reactions are called condensation reactions." "Dicarboxylic acid reacting with a diol (example of a condensation polymer) - CORRECT ANSWER lol The resultant polymer is a polyester." "Amino acids - CORRECT ANSWER An amino acid contains two different functional groups: a basic amino group (NH₂) and a carboxyl group (COOH), e.g. glycine, the smallest amino acid. Amino acids can form polypeptides via condensation polymerisation. The amino acid group can react with the acid group of another (continuously) forming a polymer chain. For every new bond formed another water molecule is lost." "Proteins - CORRECT ANSWER Proteins are multiple long chain polypeptides. They have many uses:
- Form enzymes which work as catalysts speeding up reactions in the human body
- Form Haemoglobin which in red blood cells transport oxygen around the body
- Form antibodies which are important for our immune system. They find at get rid of bacteria and viruses
- Form the majority of body tissue" "DNA - CORRECT ANSWER DNA is a large molecule essential for life that encodes genetic instructions for the development and functioning of living organisms and viruses. Most DNA molecules are two polymer chains, made from 4 different molecules called a nucleotides, in a double helix structure. The monomers that make up DNA are nucleotides." "Other naturally occurring polymers - CORRECT ANSWER Other important polymers for life are starch made from glucose monomers, cellulose made from glucose monomers and proteins made from amino acid monomers." "Number of types of monomers in addition polymerisation - CORRECT ANSWER Only one monomer type containing a C=C bond."
"Number of types of monomers in condensation polymerisation - CORRECT ANSWER Either two monomer types with the same functional groups, or one monomer type with two different functional groups." "Number of products in addition polymerisation - CORRECT ANSWER One." "Number of products in condensation polymerisation - CORRECT ANSWER Two, the polymer and a small molecule." "Function groups involved in addition polymerisation - CORRECT ANSWER A C=C bond." "Function groups involved in condensation polymerisation - CORRECT ANSWER Two reactive groups on each monomer." "Pure substance - CORRECT ANSWER A pure substance is a single element or compound, which is not mixed with anything. These melt and boil at specific temperatures, and if they don't you know they are impure." "Formulation - CORRECT ANSWER This is a mixture that has been designed for a useful purpose. These are made by mixing the components of the mixture in specific amounts, when each chemical in it has a particular purpose. These measured quantities allow the formulation to have required properties. Examples include:
- Fuels
- Cleaning agnets
- Paints
- Medicines
- Alloys
- Fertilisers
- Foods" "Definition of a pure substance - CORRECT ANSWER A substance made up of a single element or compound that is not mixed with anything." "How to determine if a substance is pure - CORRECT ANSWER It will melt and boil at a specific temperature." "Properties of an impure substance in comparison with a pure substance - CORRECT ANSWER - An impurity will lower the the melting point and increase the melting range of a pure substance.
- It also increases the boiling point and may result in a substance boiling over a wider range of temperatures." "Why an impurity lowers boiling point using the example of a solution with a dissolved salt as an impurity - CORRECT ANSWER In order to dissolve the impurity the solvent must disrupt some of its interactions with other solvent molecules. When something is
"Process of fractional distillation - CORRECT ANSWER 1. Oil is firstly heated so it turns into a gas and evaporates
- It is piped to the bottom of the column
- The gas rises up the column and it gradually cools
- Different compounds in the mixture have different condensation points, so they turn back into a liquid at different places in the column" "Properties of molecules at the top of the column - CORRECT ANSWER - Small
- Low boiling point
- Very volatile (easily evaporated)
- Flows easily
- Ignites easily" "Properties of the molecules at the bottom - CORRECT ANSWER - Large
- High boiling point
- Not very volatile
- Does not flow easily
- Does not ignite easily" "Products of fractional distillation (from bottom upwards) - CORRECT ANSWER - Bitumen: used in roads and roofs
- Heavy fuel oil: used as a fuel for ships and power stations
- Diesel: used as a fuel for some cars and trains
- Kerosene: used as a fuel for aircraft
- Petrol: used as a fuel for cars
- Liquified petroleum gases: used in domestic heating and cooking" "Trends in physical properties of hydrocarbons - CORRECT ANSWER - The shorter the molecule, the less viscous (thick, sticky) it is
- The shorter the molecule, the lower the boiling point
- The shorter the molecule, the more flammable" "Combustion in hydrocarbons - CORRECT ANSWER When a hydrocarbon is burnt in air, both hydrogen and carbon are oxidised, including a release of energy. When there is enough oxygen, the carbon will be completely oxidised, called complete combustion: Hydrocarbon + oxygen → carbon dioxide + water (g)" "Cracking - CORRECT ANSWER Cracking is the process of breaking down hydrocarbons into smaller, more useful molecules, either by steam cracking or catalytic cracking. It involves a long chain being broken down into several smaller chains. It is a
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thermal decomposition reaction, meaning it involves heating to break the molecules apart." "Process of catalytic cracking - CORRECT ANSWER 1. Heat the larger hydrocarbon until it vaporises
- Pass the vapour over a hot, powdered catalyst, e.g. aluminium oxide
- The long chain molecules split apart on the surface of the specks of catalyst" "Process of steam cracking - CORRECT ANSWER 1. Heat the larger hydrocarbon until it vaporises
- Mix the vapour with steam (water vapour)
- Heat to very high temperature (often around 850°C)
- This leads to the thermal decomposition of long chain hydrocarbons to form smaller ones" "Products of cracking - CORRECT ANSWER The products of cracking are alkanes and alkenes. Cracking is done because there is a high demand for fuels with small molecules. Alkenes are also used to produce polymers." "Alkenes - CORRECT ANSWER - A homologous series of hydrocarbons
- They have a double carbon (C=C) bond, which is their functional group
- They are unsaturated because they have two fewer hydrogen atoms than the alkane with the same number of carbon
- They are more reactive than alkanes" "Formula for alkenes - CORRECT ANSWER Cn H2n" "The first four alkenes - CORRECT ANSWER - Ethene
- Propene
- Butene
- Pentene" "Formula for ethene - CORRECT ANSWER C₂H₄" "Formula for propene - CORRECT ANSWER C₃H₆" "Formula for butene - CORRECT ANSWER C₄H₈" "Formula for pentene - CORRECT ANSWER C₅H₁₀" "Uses of alkenes - CORRECT ANSWER - Creating polymers
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"Formula for propanol - CORRECT ANSWER C₃H₇OH" "Formula for butanol - CORRECT ANSWER C₄H₉OH" "Properties of alcohols - CORRECT ANSWER - Flammable: they undergo complete combustion in air to produce carbon dioxide and water
- Soluble in water: the first four dissolve completely in water to form solutions with a pH of 7
- They react with sodium to form hydrogen (with other things)
- They oxidise to form carboxylic acids" "Uses of alcohols - CORRECT ANSWER - They are used as solvents because they can dissolve things water cannot, such as oils and fats
- They are used in perfumes and aftershave lotion due to their solvent properties
- The first four alcohols are used as fuels
- Ethanol is used in spirit burners and can be mixed with petrol and used in cars
- Ethanol is used in alcoholic drinks" "How ethanol is made - CORRECT ANSWER Ethanol used in alcoholic drinks is made by fermentation." "Word equation for fermentation - CORRECT ANSWER Sugar → carbon dioxide + ethanol In the presence of yeast" "Conditions for fermentation - CORRECT ANSWER - 37°C
- Slightly acidic
- Anaerobic conditions" "Carboxylic acids - CORRECT ANSWER - A homologous series of hydrocarbons
- They have the functional group -COOH
- This -COOH has to be represented, and it usually put on the end of the formula" "General formula for carboxylic acids - CORRECT ANSWER Cn H2n+1 COOH (but methanoic acid starts at C0)" "The first four carboxylic acids - CORRECT ANSWER - Methanoic acid
- Ethanoic acid
- Propanoic acid
- Butanoic acid" "Formula for methanoic acid - CORRECT ANSWER HCOOH" "Formula for ethanoic acid - CORRECT ANSWER CH₃COOH"
"Formula for propanoic acid - CORRECT ANSWER C₂H₅COOH" "Formula for butanoic cid - CORRECT ANSWER C₃H₇COOH" "Reaction of carboxylic acids and carbonates - CORRECT ANSWER They react with carbonates to produce carbon, dioxide, a salt, and water. The salt ends with '-anoate', e.g. Ethanoic acid + sodium carbonate → carbon dioxide + sodium ethanoate + water" "Reaction carboxylic acids with alcohol - CORRECT ANSWER They react with an alcohol in the presence of a strong acid and a catalyst (e.g. concentrated sulfuric acid) to produce an ester. These have the funcitonal group -COO-." "Word equation for reaction of carboxylic acids with alcohols - CORRECT ANSWER Alcohol + carboxylic acid → ester + water In the presence of an acid catalyst" "Example of an ester being formed - CORRECT ANSWER Ethanoic acid + ethanol → ethyl ethanoate + water In the presence of an acid catalyst. The image shows ethyl ethanoate with the -COO- bond" "Carboxylic acid and water - CORRECT ANSWER They dissolve to form acidic solutions." "Type of acid for a carboxylic acid - CORRECT ANSWER Carboxylic acids are weak acids. This means that their solutions do not contain many hydrogen ions compared with a solution of a strong acid with the same concentration. The pH of a weak acid will be higher than the pH of a strong acid, provided their concentrations are the same. In a solution of a strong acid, the molecules are fully ionised, but in a weak acid, very few of the molecules are ionised (few of the uncharged atoms have become positively charged)." "Addition polymerisation - CORRECT ANSWER Alkenes can be used to make polymers such as poly(ethene) and poly(propene) by addition polymerisation. In addition polymerisation reactions, many small molecules (monomers) join together to form large molecules (polymers). The repeating unit has the same atoms as the monomer because no other molecule is formed in the reaction. To name the polymer, it is just the alkene in brackets with poly in front e.g. poly(butene)." "Poly(ethene) - CORRECT ANSWER n is the number of monomers"
"How to calculate Rf value - CORRECT ANSWER " "REQUIRED PRACTICAL 6 - Determine the colours present in an unknown mixture of food colouring using chromatography - possible method - CORRECT ANSWER 1. Use a ruler to draw a horizontal pencil line 2 cm from a short edge of the chromatography paper. Mark five pencil spots at equal intervals across the line. Keep at least 1 cm away from each end.
- Use a glass capillary tube to put a small spot of each of the known colourings on four of the pencil spots. Then use the glass capillary tube to put a small spot of the unknown mixture on the 5th pencil spot. Try to make sure each spot is no more than 5 mm in diameter. Label each spot in pencil.
- Pour water into the beaker to a depth of no more than 1 cm.
- Tape the edge of the chromatography paper to the glass rod. The paper needs to be taped at the end furthest from the spots. Rest the rod on the top edge of the beaker. The bottom edge of the paper should dip into the water. Ensure that the:
- Pencil line is above the water surface
- Sides of the paper do not touch the beaker wall
- Wait for the water solvent to travel at least three quarters of the way up the paper. Do not disturb the beaker during this time. Carefully remove the paper. Draw another pencil line on the dry part of the paper as close to the wet edge as possible.
- Hang the paper up to dry thoroughly.
- Measure the distance in mm between the two pencil lines. This is the distance travelled by the water solvent.
- For each of the four known colours, measure the distance in mm from the bottom line to the centre of each spot.
- Determine the Rf value for each substance.
- Match the Rf value of the spots from the unknown mixture with the known values of the other colourings to determine which of them are present and if any unknown substances are present."
"REQUIRED PRACTICAL 6 - Determine the colours present in an unknown mixture of food colouring using chromatography - risk assessment - CORRECT ANSWER - Safety goggles should be worn throughout" "Test for hydrogen - CORRECT ANSWER Holding a burning splint at the open end of a test tube filled with hydrogen will result in a pop sound as hydrogen burns rapidly." "Test for oxygen - CORRECT ANSWER Inserting a glowing splint into a test tube filled with oxygen will result in the splint relighting." "Test for carbon dioxide - CORRECT ANSWER When carbon dioxide is shaken or bubbled through an aqueous solution of calcium hydroxide (limewater), the limewater will turn cloudy." "Test for chlorine - CORRECT ANSWER When damp litmus paper is put into chlorine gas, the paper is bleached and turns white." "Purpose and method of a flame test - CORRECT ANSWER Flame tests can be used to identify some metal ions (cations), these ions produce different flame colours when heated strongly, the test involves dipping a clean wire loops into a solid sample of the compound and putting it into a Bunsen burner flame. Flame tests only work if the sample compound is pure." "Ions we need to know the flame test of - CORRECT ANSWER - Potassium
- Sodium
- Lithium
- Calcium
- Copper (The four most reactive and one least reactive metal on the reactivity series we need to know)." "Ion formed by potassium and flame test colour (potassium is in group 1) - CORRECT ANSWER - K⁺
- Lilac" "Ion formed by sodium and flame test colour (sodium is in group 1) - CORRECT ANSWER - Na⁺
- Yellow" "Ion formed by lithium and flame test colour (lithium is in group 1) - CORRECT ANSWER - Li⁺
- Crimson"
- Fe³⁺ (aq) + 3OH⁻ (aq) → Fe(OH)₃ (S)" "Ion formed by copper, hydroxide test colour and ionic reaction (copper is a transition metal) - CORRECT ANSWER - Cu²⁺
- Blue
- Cu²⁺ (aq) + 2OH⁻ (aq) → Cu(OH)₂ (S)" "How to tell the difference between calcium or magnesium and aluminium seeing as they all form a white precipitate - CORRECT ANSWER Aluminium hydroxide becomes clear (dissolves) if excess sodium hydroxide solution is added." "Test for carbonates - CORRECT ANSWER Carbonates react with dilute acid to give off carbon dioxide which can be identified with the limewater test. If any substance reacts with acid to produce CO2, it must contain a carbonate ion." "Test for halides - CORRECT ANSWER Halide ions in solution produce precipitates with silver nitrate solution in the presence of dilute nitric acid." "Halogens we need to know the test for - CORRECT ANSWER - Chlorine
- Bromine
- Iodine" "Ion formed by chlorine, silver nitrate test colour and ionic reaction (chlorine is a halogen) - CORRECT ANSWER - Chloride, Cl⁻
- White
- Ag⁺ (aq) + Cl⁻ (aq) → AgCl (S)" "Ion formed by bromine, silver nitrate test colour and ionic reaction (bromine is a halogen) - CORRECT ANSWER - Bromide, Br⁻
- Cream
- Ag⁺ (aq) + Br⁻ (aq) → AgBr (S)" "Ion formed by iodine, silver nitrate test colour and ionic reaction (iodine is a halogen) - CORRECT ANSWER - Iodide, I⁻
- Yellow
- Ag⁺ (aq) + I⁻ (aq) → AgI (S)" "Advantages of instrumental methods over practical methods - CORRECT ANSWER They are a faster and more accurate/sensitive method of detecting and identifying elements and compounds" "Function of flame emission spectroscopy - CORRECT ANSWER Flame emission spectroscopy is an example of an instrumental method used to analyse metal ions in solutions."
"Process of flame emission spectroscopy - CORRECT ANSWER During flame emission spectroscopy, a sample of a metal is placed in a flame. As the electrons drop back down to the original temperature, they transfer energy as light. This light is then put into a spectroscope, where the different wavelengths are detected to produce a spectrum. This works because different atoms emit different light as a result of their different wavelengths. The intensity of the spectrum indicates the concentration of the ion in the solution." "Current composition of the Earth's atmosphere and how long it has been like this - CORRECT ANSWER - ~80% nitrogen
- ~20% oxygen
- Small proportions of other gases, including carbon dioxide, water vapour and noble gases These proportions have remained roughly the same for the past 200 million years." "Why its difficult to be sure about the development of the Earth's atmosphere - CORRECT ANSWER The development has taken place over 4.6 billion years so it is difficult to gain evidence." "The theory of the atmosphere's development starting with volcanoes - CORRECT ANSWER 1. Volcanic activity released gases that formed the early atmosphere and water vapour the condensed to form the oceans.
- Early in this period the atmosphere would be similar to Mars and Venus' today, consisting mostly of carbon dioxide with little or no gaseous oxygen.
- Volcanoes also produced nitrogen which gradually built up in the atmosphere, likely forming small proportions of methane and ammonia.
- When the oceans formed carbon dioxide dissolved in the water and carbonates were precipitated producing sediments, reducing atmospheric carbon concentration." "How oxygen levels increased - CORRECT ANSWER Algae and plants produced the oxygen that is now in the atmosphere by photosynthesis. The process started with algae 2.7 billion years ago starting the process of plant evolution which eventually resulted in enough plants to increase the percentage of oxygen to allow animals to evolve." "How carbon dioxide levels decreased - CORRECT ANSWER - Photosynthesis done by algae and plants reduced the percentage of carbon dioxide in our atmosphere
- The formation of sedimentary rocks and fossil fuels (containing carbon) also took CO₂ out the atmosphere" "The three main carbon stores - CORRECT ANSWER - Coal
- Crude oil and natural gas
"Potential effects of an increase in average global temperatures - CORRECT ANSWER
- Glaciers and polar ice melting
- Sea levels rising which could result in an increase in frequency and severity of storms
- Patterns of rainfall changing, producing floods or droughts
- Habitats changing (and pathogens move further north as temperatures become habitable)" "The significance of the varying effects of climate change - CORRECT ANSWER It could potentially mean action is harder to take, as inland government are less under threat from the effects such as rising sea levels, so have less spur to prick the sides of their intent." "Methods of reducing the international carbon footprint - CORRECT ANSWER - Using renewable energy resources over fossil fuels or improve efficiency of fossil fuel burning
- The government can reduce tax for people with a smaller carbon footprint. In the UK some businesses have greater tax based on their reliance on landfill
- Use carbon capture and storage technology, that captures the carbon before it releases into the atmosphere, it is often used in deep underground cracks in the rock such as old oil wells" "Why it is hard to carry out these methods of reducing carbon footprint - CORRECT ANSWER - It is hard to discover methods of increasing efficiency
- Governments (especially in developing nations, which often are using more energy due to a larger population) are often unwilling to increase tax when it could inhibit economic growth
- Large businesses often won't switch to renewable energy due to increased costs, making them less competitive and decreasing margins
- Individuals often don't want to inconvenience themselves, e.g. getting people to cycle to work can be hard" "Atmospheric pollutants that come from combustion of fuels - CORRECT ANSWER - Carbon dioxide
- Water vapour
- Carbon monoxide
- Sulfur dioxide
- Oxides of nitrogen" "The products of hydrocarbon based fuels combusting - CORRECT ANSWER The carbon and hydrogen is oxidised, so when enough oxygen is present complete combustion takes place. If their is a deficit of oxygen the oxidation is incomplete, resulting in incomplete combustion." "Complete combustion word equation - CORRECT ANSWER Hydrocarbon + oxygen → carbon dioxide + water vapour"
"Incomplete combustion word equation - CORRECT ANSWER Hydrocarbon + oxygen → carbon + carbon monoxide + carbon dioxide + water" "Processes leading to the formation of sulfur dioxide and oxides of nitrogen - CORRECT ANSWER If a fuel contains sulfur impurities, sulfur dioxide will be formed. Oxides of nitrogen will also form if the fuel burns at a high temperature, e.g. in internal combustion car engines. This is because, at high temperatures the nitrogen will react with oxygen in the air." "The three main atmospheric pollutants - CORRECT ANSWER - Carbon particulates
- Carbon monoxide
- Acid rain" "Properties and effects of carbon particulates - CORRECT ANSWER These are a bi- product of incomplete combustion. If inhaled they can get stuck in the lungs and cause breathing difficulties and cause respiratory difficulties. They also reflect sunlight back into space, resulting in global dimming." "Properties and effects of carbon monoxide - CORRECT ANSWER This can stop your blood from carrying oxygen around the body, as it binds to the haemoglobin instead of oxygen. This can result in fainting, coma and even death. It is colourless and odourless so not easily detected." "Properties and effects of acid rain - CORRECT ANSWER When sulfur dioxide or oxides of nitrogen mix with water in the clouds, sulfuric/nitric acid is formed, resulting in acid rain. When sulfur dioxide or oxides of nitrogen is breathed in it also causes breathing difficulties." "Uses of resources used by humans - CORRECT ANSWER - Warmth
- Shelter
- Food
- Transport" "Uses provided by natural resources - CORRECT ANSWER - Food
- Timber
- Clothing
- Fuels" "Uses provided by finite resources (earth, oceans and atmosphere) - CORRECT ANSWER - Energy
- Materials" "Improvements in agricultural and industrial processes done through chemistry - CORRECT ANSWER - Rubber used to be made from tree sap but is now made by human polymers
- Plastics are replacing a lot of wood materials, e.g. window frames
"How to extract the copper from metal compounds after bioleaching/phytomining - CORRECT ANSWER - Electrolysis
- Displacement reactions with scrap metal" "Stages assessed during life cycle assessments (LCAs) - CORRECT ANSWER - Extracting and processing of raw materials
- Manufacturing and packaging
- Use and operation during its lifetime
- Disposal at the end of its useful life, including transport and distribution at each stage" "Problems with LCAs - CORRECT ANSWER Use of water, resources, energy sources and production of some wastes can be quantified, however the environmental impact is more subjective, making LCAs not objective. This means that LCAs can be biased and reach a pre-determined conclusion, e.g. to help advertise a product." "Life cycle assessment of a plastic bag - CORRECT ANSWER Raw materials: crude oil Manufacturing and packaging: the compounds are extracted from a fractionating column, then cracking is performed, then polymerisation Using the product: can be reused or used in other things(e.g. shopping bags) Product disposal: recyclable but not biodegradable, therefore it will take up space in a landfill" "Life cycle assessment of a paper bag - CORRECT ANSWER Raw materials: timber Manufacturing and packaging: pulped timber is processed using lots of energy, and there is lots of waste Using the product: usually only used once Product disposal: biodegradable, non-toxic and recyclable" "Positive impacts of recycling and reusing - CORRECT ANSWER - Reduce use of finite resources
- Reduce use of energy sources
- Reduce waste
- Reduce environmental impacts" "Problems with getting raw materials and how to reduce this - CORRECT ANSWER Obtaining raw materials causes environmental impacts and the energy used to do so often comes from limited resources, to reduce this we should reuse products such as
glass bottles or recycle them into a different use if they are no longer needed for their original use." "Ways of reducing the use of metals - CORRECT ANSWER Metals can be recycled by melting and recasting or reforming into different products. The amount of separation required for recycling depends on the material's overlap in properties with the intended final use, e.g. some scrap steel can be added to iron from a blast furnace to reduce the amount of iron that needs to be extracted from iron ore." "Definition of corrosion - CORRECT ANSWER This is the destruction of materials by chemical reactions with substances in the environment, e.g. rusting, which requires water and air." "Methods of reducing/preventing corrosion - CORRECT ANSWER - Applying a coating which acts as a barrier, e.g. greasing, painting or electroplating
- Galvanisaiton" "Example of applying a coating which acts as a barrier - CORRECT ANSWER Aluminium has an oxide coating which protects the metal from corrosion." "Galvanisation - CORRECT ANSWER Some coatings provide a 'sacrificial' coating, which is where they are more reactive than the thing they are protecting so reaction happen with it before they happen with the protected substance, meaning that even when scratched the product is unaffected. This is done with zinc on iron." "Rust experiment - CORRECT ANSWER The nail only rusts on the tube on the left. It does not rust:
- In the middle test tube, where there was water but no oxygen (because there was no air in the water)
- In the right-hand test tube, where there was oxygen (air) but no water" "Word equation for rusting - CORRECT ANSWER Iron + oxygen + water → hydrated iron (III) oxide The product is rust, and is a brown crumbly substance." "Composition and uses of bronze - CORRECT ANSWER Composition: copper and tin Uses: statues, bells, coins" "Composition and uses of brass - CORRECT ANSWER Composition: copper and zinc Uses: musical instruments, locks and taps"
