Organic Chemistry GCSE

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What is organic chemistry?
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The study of families of carbon compounds where carbon atoms are found bonded together to form chains and/or rings. (It does not include carbon dioxide, carbon monoxide or carbonate compounds.)
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What is a homologous series?
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A homologous series is a family of compounds. The family members: – 1. share the same general formula. 2. have similar chemical properties. 3. show a gradation in physical properties. 4. differ by a CH₂ group.
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Explain what the term hydrocarbon means.
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A molecule made up of hydrogen and carbon ONLY.
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Explain what the term saturated means
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A substance made of molecules that do not have double or triple bonds between carbon atoms.
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Explain what the term unsaturated means
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Refers to molecules that have at least one double C=C bond (or triple bond).
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What does the term molecular formula mean?
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Formula giving the actual number of atoms of each element in a molecule. e.g. C₄H₁₀ for butane
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What does the term structural formula mean?
What does the term structural formula mean?
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Formula showing how the atoms are bonded together in a molecule. Butane shown here.
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What does the term empirical formula mean?
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Formula that gives the lowest whole-number ratio of atoms present in a molecule. For butane: C₂H₅
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What does the term functional group mean?
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A group of atoms responsible for the characteristic reactions of a particular compound. C=C for alkenes OH for alcohols COOH for carboxylic acids Alkanes don’t have a functional group and are the least reactive homologous series.
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What is the simplest homologous series? The alkanes or alkenes
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The alkanes. Alkanes do not have a ‘functional group’ and are the least reactive homologous series.
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Are the alkanes saturated or unsaturated hydrocarbons?
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The alkanes are saturated hydrocarbons. Propane shown here.
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Name the first six alkanes
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Methane, ethane, propane, butane, pentane and hexane. (Then heptane, octane, nonane and decane.)
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Write the general formula for alkanes
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CnH2n+2 The n and 2n+2 should be subscripts. 2n indicates that for every carbon in the chain there are 2 hydrogens. The +2 indicates the need for a further 2 hydrogens to complete the two ends of the chain.
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An alkane has 16 Carbon atoms, what is its molecular formula
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C₁₆H₃₄
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What is our main source of alkanes?
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Fossil fuels.
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How are alkanes separated from the mixture of hydrocarbons in crude oil?
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By Fractional Distillation.
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Give a brief outline of fractional distillation (fractionation) of crude oil.
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Oil is heated to 360°C. All but the bitumen fraction vaporize. The vapour condenses as it ascends the fractionating column. The higher the b.p. the sooner it condenses. The refinery gases (methane – butane) leave at the top.
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A labeled diagram of a fractionating column.
A labeled diagram of a fractionating column.
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(Top – Down): Refinery gases Petrol Naphtha Paraffin Diesel Fuel oil Bitumen
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How does the viscosity (runniness) of the crude oil fraction change as you move from petrol to fuel oil
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Viscosity increases. The fractions become less runny.
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How does burning of the crude oil fraction change as you move from petrol to fuel oil
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They burn less and less well and produce increasing amounts of black smoke and soot (unburnt carbon). From paraffin-down, a wick need to be used to keep the fraction burning.
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Why do alkanes require a lot of energy to break their bonds?
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Because the C-C and C-H covalent bonds are strong, requiring a relatively large amount of energy to break them apart.
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Are the alkenes saturated or unsaturated hydrocarbons?
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Alkenes are unsaturated hydrocarbons. All members of the alkene family have one C=C bond.
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What is the general formula for alkenes?
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CnH2n The n and 2n should be written as subscripts. They begin at n=2 (ethene) as you need at least 2 carbons to have a C=C in the molecule.
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What makes alkenes more reactive than alkanes?
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Alkenes have a C=C functional group. One of the covalent bonds of the double bond is weaker than the other, making it more reactive.
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What happens when bromine water is added to an alkene?
What happens when bromine water is added to an alkene?
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The orange coloured bromine water is immediately decolourised. The image shows a liquid alkene mixed with bromine water. The liquids are immiscible, but when shaken together the orange colour is decolourised.
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What type of reaction occurs when alkenes react with bromine?
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An ADDITION REACTION C₂H₄ + Br₂ → C₂H₄Br₂ ‘addition’ as 2 molecules add together to give a single molecule.
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What can be used to distinguish between an alkane and an alkene?
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The test with bromine water. With the alkane the bromine water stays orange, but with the alkene it is decolourised.
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How is crude oil formed?
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Formed over millions of years when plankton and other sea creatures die, fall to the sea bed and become covered by layers of sand and silt. Sand and silt means that no oxygen gets to the dead bodies. The heat and pressure builds up and slowly turns them to hydrocarbons.
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What are the conditions like at the top of the fractionating column? Describe the molecules you would find there.
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Low temperatures, about 70 degrees. You would find smaller molecules which are light in colour, very volatile, have a low viscosity and are very flammable.
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What are the conditions like at the bottom of the fractionating column? Describe the molecules you would find there.
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High temperatures, about 360 degrees. You would find larger molecules which are dark in colour, difficult to light, have a high boiling point, low volatility and thick and viscous.
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What does the fractional distillation of crude oil do to the crude oil?
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It separates the mixture of hydrocarbons into more useful products.
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The fractional distillation of crude oil is described as a continuous process. What does this mean?
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Constantly feeding in vapourised crude oil and constantly removing fractions as they are formed. The opposite is a ‘batch process’ such as is used in the brewing industry.
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What is a fuel
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A fuel is a substance that burns to release energy.
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What is a fraction?
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A fraction is a group of similar sized molecules with similar boiling points.
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What is a carbon chain?
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A line of connected carbon atoms that have covalent bonds.
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If alkanes burn in a plentiful supply of oxygen what do they produce?
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Carbon dioxide and water. This is called ‘complete combustion’.
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Complete and balance the following 2 equation for complete combustion: CH₄ + O₂ → C₄H₁₀ + O₂ →
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CH₄ + 2O₂ → CO₂ + 2H₂O C₄H₁₀ + 6¹/₂O₂ → 4CO₂ + 5H₂O or 2C₄H₁₀ + 13O₂ → 8CO₂ + 10H₂O
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What is incomplete combustion in reference to hydrocarbons and what are the products.
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Incomplete combustion happens when the hydrocarbon is burnt in a poor supply of oxygen. Carbon monoxide and steam are the products. CO is known as the ‘silent killer’/
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Does incomplete combustion produce as much energy as complete combustion.
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No. It produces significantly less energy. e.g. for methane: complete (890 units of energy released) incomplete (283 units of energy released)
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In the experiment to test the combustion products of methane what was the purpose of the inverted funnel?
In the experiment to test the combustion products of methane what was the purpose of the inverted funnel?
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To increase the surface area in order to catch as much combustion products (gas) as possible.
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In the experiment to test the combustion products of methane what was the purpose of the ice/water mixture?
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To condense the water vapour to water.
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In the experiment to test the combustion products of methane what was the purpose of the vacuum pump?
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To draw (suck) the combustion products through the apparatus.
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In the experiment to test the combustion products of methane what was the purpose of the anhydrous copper (II) sulfate and limewater.
In the experiment to test the combustion products of methane what was the purpose of the anhydrous copper (II) sulfate and limewater.
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White anhydrous copper sulfate turns from white to blue when water is added. Limewater turns from clear and colourless to cloudy/milky when CO₂ is added.
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Write down any observations that you would see in the experiment to test the combustion products of methane.
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Lime water turns cloudy showing carbon dioxide is present. Anhydrous cobalt chloride paper turns from blue to pink showing water was present. Anhydrous copper sulphate turned from white to blue showing water was present.
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Write down a conclusion you could take from the experiment to test the combustion products of methane
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Combustion products of methane are carbon dioxide and water (in a plentiful air supply)
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What happens if a hydrocarbon fuel is burnt in an insufficient oxygen supply?
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Incomplete combustion occurs.
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What are the products of incomplete combustion?
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Carbon monoxide and carbon.
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Describe the characteristics of carbon monoxide and the harmful biological consequences of inhaling it.
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Carbon monoxide it a tasteless, colourless, odourless gas that combines with haemoglobin in the red blood cells. The blood cannot carry as much oxygen. It causes drowsiness and headaches and can eventually lead to death.
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Describe the characteristics of soot (unburnt carbon) and the biological consequences of inhaling it.
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Carbon is a black powder. It is seen as soot. Inhaling carbon particulates worsens asthma and other breathing problems.
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Ethanol is a member of which homologous series?
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The alcohols. Proper name alkANOLS. e.g. ethANOL
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What is the functional group of all alcohols?
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An -O-H group, known as a hydroxyl group.
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What is the general formula for ethanol?
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CnH2n+1OH The n and 2n+1 should be subscripts.
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What are the two ways in which ethanol can be manufactured?
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1. Fermentation of sugars 2. Hydration of ethene
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What materials and conditions are required for fermentation?
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Materials: Sugar and Yeast. Conditions: Warmth (35-40⁰C) Anaerobic (oxygen kept out)
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What would result if oxygen was present during fermentation?
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Ethanol would form, but it would then oxidise to ethanoic acid (vinegar).
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What is the use of lime water in fermentation of sugars in order to make ethanol?
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1. Test for whether CO2 is released 2. lets out CO2 but prevents air from entering the yeast – acts as an airlock 3. Shows the rate of fermentation
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What is the boiling point of ethanol?
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78⁰C
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What determines the alcoholic drink? Give an example
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The source of sugar. Wine from grapes. Beer from hops. Cider from apples.
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How is ethanol manufactured in the hydration of ethene method?
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Adding steam to ethene.
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Write a balanced symbol equation, including state symbols, for the hydration of ethane.
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C₂H₄(g) + H₂O(g) → C₂H₅OH(g) Hydration means to react with water/steam. This is also classified as an ‘addition reaction’.
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What conditions are needed for the manufacture of ethene in the hydration of ethene method?
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Temperature of 300 ⁰C. Pressure of about 60-70 atm. Catalyst of phosphoric acid.
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What type of reaction occurs during the hydration of ethene method to make ethanol?
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Addition reaction. C₂H₄(g) + H₂O(g) → C₂H₅OH(g) 2 molecules combine to form just 1.
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Which process to make ethanol is continuous?
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Hydration of ethene. The product is removed at one end and more reactants passed in at the other. The ‘batch process’ used in brewing/fermentation, is less efficient, but it doesn’t require the same high temperatures and pressures to be maintained.
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Is sugar cane a renewable source of energy?
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Yes. In some countries several harvests of sugar cane are possible in the same year.
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Is crude oil a renewable source of energy?
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No, it is finite. To be renewable it need to be replaceable within a lifetime. Crude oil took many millions of years to form.
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Complete and balance the following equation to show the complete combustion of ethanol: C₂H₅OH + O₂ →
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C₂H₅OH +3O₂ → 2CO₂ + 3H₂O
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Complete and balance the following equation to show the incomplete combustion of ethanol: C₂H₅OH + O₂ →
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C₂H₅OH + 2O₂ → 2CO + 3H₂O
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What is methylated spirits?
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Methylated spirits is 99% ethanol. The rest is poisonous methanol and tiny amounts of chemicals intentionally added to deter drinking.
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Give several uses of ethanol.
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Alcoholic beverages. Solvent for cosmetics. A fuel.
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What is the general formula of a carboxylic acid? Proper name alkANOIC ACIDS. e.g. ethANOIC ACID
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CnH2n+1COOH The n and 2n+1 should be written as subscripts. In assigning the prefix of the name (e.g. eth) you must count the C atom of the COOH functional group.
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The name and molecular formula of the first member of the carboxylic acids. [Hint: in this case use n = 0)
The name and molecular formula of the first member of the carboxylic acids. [Hint: in this case use n = 0)
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Methanoic acid HCOOH
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For ethanoic acid, give both its molecular and structural formulae.
For ethanoic acid, give both its molecular and structural formulae.
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molecular: CH₃COOH structural: shown in image
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A 5% solution of ethanoic acid in water is better known as
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vinegar
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Describe a test to distinguish between an alcohol and a liquid alkane.
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Heat with acidified potassium dichromate in a test tube placed in a boiling water bath. With the alkane the orange colour will remain, but with the alcohol, it will change to dark green.
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The pH of a dilute solution of ethanoic acid.
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3
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Complete and balance the following equation to show how ethanoic acid reacts with magnesium: Mg + CH₃COOH → Name the organic salt formed.
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Mg + 2CH₃COOH → Mg(CH₃COO)₂ + H₂↑ This is a ‘MASH’ reaction. Magnesium ethanoate is the organic salt.
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Complete and balance the following equation to show how ethanoic acid reacts with sodium hydroxide solution: NaOH + CH₃COOH → Name the organic salt formed.
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NaOH + CH₃COOH → CH₃COONa + H₂O This is a ‘neutralisation’ reaction. Sodium ethanoate is the organic salt.
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Complete and balance the following equation to show how ethanoic acid reacts with sodium carbonate solution: Na₂CO₃ + CH₃COOH → Name the organic salt formed.
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Na₂CO₃ + 2CH₃COOH → 2CH₃COONa + H₂O + CO₂↑ Sodium ethanoate is the organic salt.
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Give 2 uses of ethanoic acid.
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Vinegar. Pickling. Limescale remover.
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Complete the following equation to show the polymerization of ethane. n H₂C=CH₂ →
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n H₂C=CH₂ → (H₂C-CH₂)n The image shows it better. n = several thousand
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Give several uses of polythene.
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Plastic shopping bags. Plastic toys. Plastic sheets. Plastic aprons and gloves.
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Complete the following equation to show the polymerization of chloroethene. n H₂C=CHCl →
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n H₂C=CHCl → (H₂C-CHCl)n The image shows it better. n = several thousand. chloroethene used to be called vinylchloride
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Give several uses of polychloroethene (polyvinylchloride PVC)..
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Plastic windows & guttering. Vinyl flooring. Waterproof clothing.
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What kind of polymers are polythene and PVC?
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Addition polymers. The other type (including nylon and terylene) are ‘condensation polymers’.
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Are addition polymers (e.g. polythene and PVC) biodegradable?
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No.
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Are condensation polymers (e.g. nylon and terylene) biodegradable?
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Yes.
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The 2 main ways of disposing of polymer waste.
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Landfill and incineration.
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One benefit and one drawback of using incineration to dispose of addition polymers like polythene and polychloroethene.
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Benefits. The heat produced can be made use of. Less solid left to be sent to landfill. Drawbacks. Produces CO₂ that contributes to global warming. Produces toxic gases.
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Apart from incineration and landfill, what else can be done with waste plastics?
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Recycling. Plastic recycling is the process of recovering scrap or waste plastic and reprocessing the material into useful products.

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