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GCSE · Chemistry

C7b Alcohols, Carboxylic Acids and Polymers

AQA 8464 · Calculator allowed · about 120 minutes

Total Marks

Name: _______________________________ Date: ____ / ____ / ______

Answer ALL questions. Show all your working.

Bioethanol as a transport fuel

Revision Library resource team

In the UK, most standard unleaded petrol sold at the pump (called E10) is a blend containing up to 10% bioethanol. Bioethanol is produced by fermenting sugars from crops such as sugar beet or wheat using yeast, then distilling the mixture to increase the ethanol concentration. Blending bioethanol with petrol reduces the amount of crude oil needed to make each litre of fuel. However, growing crops specifically for bioethanol production uses agricultural land and water that could otherwise grow food crops, and processing the crops into fuel itself requires energy.

Alcohols are a homologous series of organic compounds.

(a)Define the term 'homologous series'.(2)

(b)The table shows the first four alcohols. Complete the table by giving the missing name or molecular formula.

Carbon atoms	Name	Molecular formula
1	methanol	CH3OH
2	(i)	C2H5OH
3	propan-1-ol	(ii)
4	butan-1-ol	C4H9OH

(3)

(c)Name the functional group found in all alcohols, and give its formula.(2)

(Total for Question 1 is 7 marks)

Ethanol and propan-1-ol are both members of the alcohol homologous series.

(a)Draw the displayed structural formula of ethanol, showing all atoms and all covalent bonds.(2)

(b)Give the molecular formula of propan-1-ol.(1)

(c)State the number of carbon atoms in a molecule of butan-1-ol and, using the general formula for alcohols, deduce its molecular formula.(2)

(Total for Question 2 is 5 marks)

Read the source text 'Bioethanol as a transport fuel' before answering this question.

(a)State two everyday uses of ethanol, other than as a fuel.(2)

(b)Using the information in the source text, suggest one advantage and one disadvantage of using bioethanol as a transport fuel.(2)

(c)Explain why ethanol is often described as a 'carbon neutral' fuel in principle, but why bioethanol production is not always truly carbon neutral in practice.(3)

(Total for Question 3 is 7 marks)

Ethanol can be produced by the fermentation of sugar solution.

(a)Name the microorganism used in fermentation, and name the enzyme it contains that catalyses the reaction.(2)

(b)State two conditions needed for fermentation to occur.(2)

(c)Write a balanced symbol equation for the fermentation of glucose, C6H12O6.(2)

(Total for Question 4 is 6 marks)

Alcohols burn in a plentiful supply of oxygen.

(a)State the two products of the complete combustion of an alcohol.(2)

(b)Balance the symbol equation for the complete combustion of butan-1-ol: ___C4H9OH + ___O2 -> ___CO2 + ___H2O(2)

(c)Calculate the maximum mass of carbon dioxide produced when 9.2 g of ethanol, C2H5OH, is completely combusted, using the equation C2H5OH + 3O2 -> 2CO2 + 3H2O. (Mr of C2H5OH = 46, Mr of CO2 = 44)(3)

(Total for Question 5 is 7 marks)

A small piece of sodium is added to a test tube of ethanol.

(a)By analogy with the reaction of sodium with water, describe what you would observe.(2)

(b)Name the gas produced in this reaction.(1)

(c)Write a balanced symbol equation for the reaction between sodium and ethanol.(2)

(Total for Question 6 is 5 marks)

Ethanol can be oxidised to form ethanoic acid.

(a)State two ways in which ethanol can be oxidised to form ethanoic acid.(2)

(b)Complete and balance the equation for the oxidation of ethanol, using [O] to represent oxygen from the oxidising agent: CH3CH2OH + ___[O] -> ___ + H2O(3)

(c)Name the carboxylic acid formed when propan-1-ol is fully oxidised.(1)

(Total for Question 7 is 6 marks)

Carboxylic acids are a homologous series of organic compounds.

(a)State the general formula for the carboxylic acids.(1)

(b)The table shows the first four carboxylic acids. Complete the table.

Carbon atoms (inc. COOH carbon)	Name	Molecular formula
1	methanoic acid	HCOOH
2	(i)	CH3COOH
3	propanoic acid	(ii)
4	butanoic acid	C3H7COOH

(3)

(c)Name the functional group found in carboxylic acids, and give its formula.(2)

(Total for Question 8 is 6 marks)

A student carries out an experiment, first adding a few drops of universal indicator to dilute ethanoic acid, then separately reacting a sample of the same acid with calcium carbonate chips.

(a)Higher tier only. Carboxylic acids are described as 'weak acids'. Explain what this means in terms of ionisation, and state how this affects the pH of the ethanoic acid compared with a strong acid of the same concentration.(3)

(b)Describe a method, including a positive test result, that the student could use to show that carbon dioxide gas is produced when calcium carbonate is added to the dilute ethanoic acid.(3)

(c)Write a balanced symbol equation, including state symbols, for the reaction between ethanoic acid and calcium carbonate.(3)

(Total for Question 9 is 9 marks)

Required practical: a student carries out an experiment to prepare a small sample of an ester from ethanoic acid and ethanol.

(a)State the two reagents used to prepare the ester, and name the catalyst added to the reaction mixture.(3)

(b)The mixture is gently warmed in a water bath rather than heated directly with a Bunsen burner flame. Explain why.(2)

(c)After heating, the mixture is poured into a solution of sodium carbonate. Describe the observation made and explain the purpose of this step.(3)

(d)Calculate the maximum theoretical mass of ethyl ethanoate that could be produced from 6.0 g of ethanoic acid, assuming ethanol is present in excess. (Mr of ethanoic acid = 60, Mr of ethyl ethanoate = 88)(3)

(e)The student's actual yield of ester was 6.2 g. Calculate the percentage yield, giving your answer to 3 significant figures.(2)

(Total for Question 10 is 13 marks)

Higher tier only (Chemistry triple award). A carboxylic acid reacts with an alcohol to form an ester.

(a)Name the type of reaction that occurs between a carboxylic acid and an alcohol, and name the small molecule released.(2)

(b)Propanoic acid, C2H5COOH, reacts with methanol, CH3OH, to form an ester. Write a balanced symbol equation for this reaction and name the ester formed.(3)

(Total for Question 11 is 5 marks)

Esters are used in a variety of everyday products.

(a)State two properties of esters that make them useful in perfumes.(2)

(b)State one other everyday use of esters, other than in perfumes.(1)

(Total for Question 12 is 3 marks)

Ethanoic acid (Mr = 60) reacts with ethanol (Mr = 46) to form ethyl ethanoate (Mr = 88) and water. (Ar: H = 1, C = 12, O = 16)

(a)Calculate the relative formula mass (Mr) of methanoic acid, HCOOH.(2)

(b)Calculate the percentage by mass of oxygen in methanoic acid. Give your answer to 1 decimal place.(2)

(c)Higher tier only. Calculate the atom economy for the formation of ethyl ethanoate in this reaction. Give your answer to 1 decimal place.(2)

(Total for Question 13 is 6 marks)

Alkenes such as ethene and propene can undergo addition polymerisation.

Figure (to be drawn): Space for students to draw the repeating unit of poly(propene) with bracket and subscript n.

(a)Define addition polymerisation.(2)

(b)Propene, CH2=CHCH3, undergoes addition polymerisation to form poly(propene). Draw the repeating unit of poly(propene), including the bracket and subscript n.(3)

(Total for Question 14 is 5 marks)

Higher tier only (Chemistry triple award). A polyester can be made by reacting a diol (a molecule with two -OH groups) with a dicarboxylic acid (a molecule with two -COOH groups).

(a)State the type of small molecule released when the diol and dicarboxylic acid join together, and name the type of chemical link formed between the monomers.(2)

(b)Explain one difference between condensation polymerisation and addition polymerisation.(3)

(Total for Question 15 is 5 marks)

Higher tier only (Chemistry triple award). Compare addition polymerisation and condensation polymerisation. In your answer, refer to the type(s) of monomer used, the type of link/repeating unit formed, and whether a by-product is released. Use named examples to support your answer.

(Total for Question 16 is 6 marks)

Higher tier only (Chemistry triple award). Amino acids are the monomers used to build proteins.

(a)State the two functional groups found in an amino acid molecule.(2)

(b)Two amino acid molecules can join together, releasing a small molecule, to form a dipeptide. Name the small molecule released, and name the type of bond that forms between the two amino acids.(2)

(c)A simple amino acid, glycine, has the molecular formula C2H5NO2 (Mr = 75). When two molecules of glycine join to form a dipeptide, one molecule of water (Mr = 18) is released. Calculate the relative formula mass of the dipeptide formed.(2)

(d)Explain how many amino acid molecules join together to form a protein, and name this type of large molecule.(2)

(Total for Question 17 is 8 marks)

Higher tier only (Chemistry triple award). DNA is a polymer found in the nucleus of cells.

(a)Name the monomer molecules that DNA is made from, and state how many different types of these monomers are found in DNA.(2)

(b)Describe the overall structure of a DNA molecule.(2)

(c)Explain the importance of the sequence of nucleotides along a strand of DNA.(2)

(Total for Question 18 is 6 marks)

Mark scheme · C7b Alcohols, Carboxylic Acids and Polymers

Question 1

(a) B1 a family/series of compounds that all share the same general formula, oe
(a) B1 each successive member differs from the last by a CH2 unit, showing a gradual trend in physical properties and similar chemical properties, oe
(a) Answer: A homologous series is a family of compounds with the same general formula, in which each member differs from the next by a CH2 unit, and which shows a gradual trend in physical properties and similar chemical properties.
(b) B1 (i) ethanol
(b) B1 (ii) C3H7OH cao
(b) B1 general formula for the alcohols correctly stated as CnH2n+1OH
(b) Answer: (i) ethanol; (ii) C3H7OH; general formula CnH2n+1OH
(c) B1 hydroxyl group
(c) B1 -OH cao
(c) Answer: Hydroxyl group, -OH.

Question 2

(a) M1 correct skeleton showing two carbon atoms singly bonded to each other, with the second carbon also singly bonded to the oxygen atom
(a) A1 all five hydrogen atoms correctly placed (three on the first carbon, two on the second carbon) and the O-H bond shown
(a) Answer: A chain of two carbon atoms joined by a single C-C bond; the first carbon carries three hydrogen atoms, the second carbon carries two hydrogen atoms and is bonded to the oxygen atom, and the oxygen atom carries one hydrogen atom (H3C-CH2-O-H).
(b) B1 C3H7OH cao (accept C3H8O)
(b) Answer: C3H7OH
(c) M1 4 carbon atoms
(c) A1 C4H9OH cao
(c) Answer: 4 carbon atoms; C4H9OH

Question 3

(a) B1 any one of: solvent (e.g. in perfumes, inks, cosmetics, hand sanitiser)
(a) B1 any other one of: in alcoholic drinks; as methylated spirits (a cleaning solvent/fuel for camping stoves)
(a) Answer: E.g. as a solvent (in perfumes, inks or hand sanitiser); in alcoholic drinks.
(b) B1 advantage, e.g. made from renewable plant material, so does not use up finite crude oil reserves, oe
(b) B1 disadvantage, e.g. land and water used to grow fuel crops could instead grow food, which may reduce food supply/raise food prices, oe
(b) Answer: Advantage: made from a renewable resource (plant crops), so does not deplete finite crude oil reserves. Disadvantage: land and water used to grow fuel crops could instead be used to grow food, which could reduce food supply or raise food prices.
(c) B1 the crop plants absorb carbon dioxide from the atmosphere by photosynthesis as they grow, oe
(c) B1 this can balance/cancel out the carbon dioxide released when the bioethanol is later burned, giving no net increase in atmospheric CO2 in theory, oe
(c) B1 in practice, energy is used (e.g. farm machinery, fertiliser production, transport and processing, as suggested by the source text) which releases additional CO2, so bioethanol production is not perfectly carbon neutral, oe
(c) Answer: Growing plants absorb carbon dioxide by photosynthesis, which in theory balances the CO2 released when the bioethanol is burned, giving no net increase in atmospheric CO2. In practice, energy is used for farming, fertiliser production, transport and processing, which releases additional CO2, so it is not truly carbon neutral.

Question 4

(a) B1 yeast
(a) B1 zymase (accept 'enzymes in yeast')
(a) Answer: Yeast; the enzyme zymase.
(b) B1 warm temperature (approximately 25-40 degrees C)
(b) B1 anaerobic conditions (absence of oxygen/air)
(b) Answer: A warm temperature (around 25-40 degrees C); anaerobic conditions (no oxygen present).
(c) M1 correct products, ethanol and carbon dioxide
(c) A1 correctly balanced: C6H12O6 -> 2C2H5OH + 2CO2 cao
(c) Answer: C6H12O6 -> 2C2H5OH + 2CO2

Question 5

(a) B1 carbon dioxide
(a) B1 water
(a) Answer: Carbon dioxide and water.
(b) M1 4CO2 and 5H2O (carbon and hydrogen atoms balanced)
(b) A1 6O2 added so oxygen atoms balance; final equation C4H9OH + 6O2 -> 4CO2 + 5H2O cao
(b) Answer: C4H9OH + 6O2 -> 4CO2 + 5H2O
(c) M1 moles of ethanol = 9.2 / 46 = 0.2 mol
(c) M1 moles of CO2 = 0.2 x 2 = 0.4 mol, using the 1:2 mole ratio (ft from their moles of ethanol)
(c) A1 mass of CO2 = 0.4 x 44 = 17.6 g cao (ft)
(c) Answer: 17.6 g

Question 6

(a) B1 effervescence/fizzing, as bubbles of gas are produced, oe
(a) B1 the sodium gradually gets smaller until it disappears; the reaction is less vigorous than with water, oe
(a) Answer: Fizzing (effervescence) is seen as a gas is produced, and the piece of sodium gradually gets smaller until it disappears. The reaction is less vigorous than the reaction of sodium with water.
(b) B1 hydrogen
(b) Answer: Hydrogen.
(c) M1 correct formula for sodium ethoxide, CH3CH2ONa, as a product
(c) A1 fully balanced: 2CH3CH2OH + 2Na -> 2CH3CH2ONa + H2 cao
(c) Answer: 2CH3CH2OH + 2Na -> 2CH3CH2ONa + H2

Question 7

(a) B1 by the action of microorganisms/bacteria in the air (as happens when wine turns to vinegar), oe
(a) B1 by reaction with an oxidising agent, e.g. potassium dichromate(VI) solution, oe
(a) Answer: By the action of microorganisms in the air (e.g. when wine turns to vinegar); or by reaction with an oxidising agent such as potassium dichromate(VI) solution.
(b) M1 correct organic product, CH3COOH
(b) M1 coefficient of 2 for [O]
(b) A1 fully balanced equation: CH3CH2OH + 2[O] -> CH3COOH + H2O cao
(b) Answer: CH3CH2OH + 2[O] -> CH3COOH + H2O
(c) B1 propanoic acid
(c) Answer: Propanoic acid.

Question 8

(a) B1 CnH2n+1COOH
(a) Answer: CnH2n+1COOH
(b) B1 (i) ethanoic acid
(b) B1 (ii) C2H5COOH cao
(b) B1 both rows fully correct and consistent, oe
(b) Answer: (i) ethanoic acid; (ii) C2H5COOH
(c) B1 carboxyl group (carboxylic acid group)
(c) B1 -COOH cao
(c) Answer: Carboxyl group, -COOH.

Question 9

(a) B1 a weak acid only partially ionises/dissociates in aqueous solution, oe
(a) B1 so it produces fewer H+ ions than a strong acid of the same concentration, oe
(a) B1 so the carboxylic acid has a higher pH (is less acidic) than a strong acid of the same concentration, oe
(a) Answer: A weak acid only partially ionises in aqueous solution, producing fewer H+ ions than a strong acid of the same concentration, so it has a higher pH (is less acidic) than a strong acid of the same concentration.
(b) B1 collect the gas produced and bubble/pass it through limewater, oe
(b) B1 using a delivery tube connecting the reaction vessel to a test tube of limewater, oe
(b) B1 positive result: the limewater turns cloudy/milky if carbon dioxide is present
(b) Answer: Collect the gas given off using a delivery tube and bubble it through limewater. If carbon dioxide is present, the limewater turns cloudy (milky).
(c) M1 correct formula for calcium ethanoate, (CH3COO)2Ca
(c) M1 correctly balanced: 2CH3COOH + CaCO3 -> (CH3COO)2Ca + H2O + CO2
(c) A1 correct state symbols throughout: 2CH3COOH(aq) + CaCO3(s) -> (CH3COO)2Ca(aq) + H2O(l) + CO2(g) cao
(c) Answer: 2CH3COOH(aq) + CaCO3(s) -> (CH3COO)2Ca(aq) + H2O(l) + CO2(g)

Question 10

(a) B1 ethanoic acid
(a) B1 ethanol
(a) B1 (concentrated) sulfuric acid
(a) Answer: Ethanoic acid; ethanol; concentrated sulfuric acid (catalyst).
(b) B1 ethanol and the ester product are flammable/volatile, so an open flame risks the vapour catching fire, oe
(b) B1 a water bath provides gentler, more even heating, which is safer and reduces evaporation of the flammable liquids, oe
(b) Answer: Ethanol and the ester are flammable and volatile, so heating with a naked flame risks the vapour catching fire. A water bath provides gentler, more even heating, which is safer.
(c) B1 observation: fizzing/effervescence (bubbles of gas seen)
(c) B1 purpose: neutralises the leftover sulfuric acid catalyst and any unreacted ethanoic acid, oe
(c) B1 so the ester (which does not mix with water and forms a separate layer) can be identified/separated cleanly, oe
(c) Answer: Fizzing (effervescence) is observed as carbon dioxide gas is released. The sodium carbonate neutralises the leftover sulfuric acid catalyst and unreacted ethanoic acid, so the ester (which forms a separate layer and does not mix with water) can be identified and separated cleanly.
(d) M1 moles of ethanoic acid = 6.0 / 60 = 0.1 mol
(d) M1 mole ratio acid:ester is 1:1, so moles of ester = 0.1 mol (ft)
(d) A1 mass of ester = 0.1 x 88 = 8.8 g cao (ft)
(d) Answer: 8.8 g
(e) M1 % yield = (actual yield / theoretical yield) x 100 = (6.2 / 8.8) x 100 (ft from part d)
(e) A1 = 70.5% (awrt 70.5, ft)
(e) Answer: 70.5%

Question 11

(a) B1 esterification (a condensation reaction)
(a) B1 water
(a) Answer: Esterification (a condensation reaction); water is released.
(b) M1 correct ester formula, C2H5COOCH3
(b) M1 fully balanced equation: C2H5COOH + CH3OH -> C2H5COOCH3 + H2O
(b) A1 correct name: methyl propanoate cao
(b) Answer: C2H5COOH + CH3OH -> C2H5COOCH3 + H2O; the ester formed is methyl propanoate.

Question 12

(a) B1 volatile (evaporate easily)
(a) B1 have a strong, pleasant (often fruity/sweet) smell
(a) Answer: Esters are volatile (evaporate easily) and have strong, pleasant (often fruity) smells.
(b) B1 as flavourings in food, or as a solvent (e.g. in nail varnish/nail varnish remover), oe
(b) Answer: As flavourings in food (or as a solvent, e.g. in nail varnish remover).

Question 13

(a) M1 correct working shown, e.g. 1 + 12 + 16 + 16 + 1
(a) A1 Mr = 46 cao
(a) Answer: 46
(b) M1 correct fraction, (32/46) x 100 (ft from part a)
(b) A1 = 69.6% (awrt 69.6, ft)
(b) Answer: 69.6%
(c) M1 atom economy = (Mr of desired product / sum of Mr of all reactants) x 100 = (88 / (60+46)) x 100
(c) A1 = 83.0% (awrt 83.0)
(c) Answer: 83.0%

Question 14

(a) B1 many small, unsaturated monomer molecules (each containing a C=C double bond) join together, oe
(a) B1 to form one long-chain polymer molecule, with no other product formed, oe
(a) Answer: Addition polymerisation is a reaction in which many small, unsaturated monomer molecules (each containing a C=C double bond) join together to form one long-chain polymer molecule, with no other product formed.
(b) M1 correct repeat unit skeleton -CH2-CH(CH3)-, with the C=C converted to a single C-C bond
(b) M1 bonds shown correctly extending through both sides of the bracket to show the chain continues
(b) A1 correct square bracket with subscript n placed outside, cao
(b) Answer: [-CH2-CH(CH3)-]n : a repeating unit of -CH2-CH(CH3)- enclosed in square brackets, with n as a subscript outside and the bonds extending through the brackets to show the chain continues.

Question 15

(a) B1 water
(a) B1 ester link(s)
(a) Answer: Water is released; an ester link is formed between the monomers.
(b) B1 condensation polymerisation typically uses two different monomers, each with (at least) two functional groups, whereas addition polymerisation uses one type of unsaturated monomer, oe
(b) B1 condensation polymerisation releases a small molecule (e.g. water) as a by-product each time a bond forms between monomers, oe
(b) B1 addition polymerisation does not release any other/by-product, oe
(b) Answer: In condensation polymerisation, two different monomers are used, each with two functional groups, and a small molecule such as water is released as a by-product each time a bond forms between monomers. In addition polymerisation, only one type of unsaturated (alkene) monomer is used, and no other product is formed.

Question 16

Level 1 (1-2): Basic, isolated statement(s) about polymerisation with little or no comparison. Little or no reference to monomers, links or by-products. Examples may be missing or incorrect.
Level 2 (3-4): Relevant points about both types of polymerisation are made, with some links between them. At least one correct example is given. Some scientific terminology is used, but the comparison may be incomplete or contain minor inaccuracies.
Level 3 (5-6): A clear, logically structured comparison of addition and condensation polymerisation, correctly explaining the type(s) of monomer used, the type of link/repeating unit formed, and whether a by-product is released, supported by at least one correct named example of each. Accurate scientific terminology is used throughout.
Indicative content:
- Addition polymerisation uses one type of monomer, which must be unsaturated (contains a C=C double bond), e.g. ethene forming poly(ethene) or propene forming poly(propene).
- In addition polymerisation, the double bond opens up and monomers join directly together; no other (by-)product is formed.
- Condensation polymerisation usually uses two different monomers, each with two functional groups (e.g. a diol and a dicarboxylic acid, or an amino acid with both -NH2 and -COOH groups).
- In condensation polymerisation, a small molecule (usually water) is released as a by-product each time a new bond (e.g. an ester link or amide/peptide link) forms between monomers.
- Example of a condensation polymer: a polyester formed from a diol and a dicarboxylic acid, linked by ester bonds; or a polypeptide formed from amino acids, linked by peptide (amide) bonds.
- Both processes produce very large, long-chain polymer molecules made of many repeating units.

Question 17

(a) B1 amine group, -NH2
(a) B1 carboxyl (carboxylic acid) group, -COOH
(a) Answer: An amine group (-NH2) and a carboxyl group (-COOH).
(b) B1 water
(b) B1 peptide bond (amide link)
(b) Answer: Water is released; a peptide bond (amide link) forms between the amino acids.
(c) M1 correct method: (2 x 75) - 18
(c) A1 = 132 cao
(c) Answer: 132
(d) B1 many amino acid molecules join together, via repeated condensation reactions (releasing water each time), oe
(d) B1 forming a long-chain molecule called a polypeptide (protein)
(d) Answer: Many amino acid molecules join together by repeated condensation reactions, releasing water each time, forming a long-chain molecule called a polypeptide (protein).

Question 18

(a) B1 nucleotides
(a) B1 four (different types)
(a) Answer: Nucleotides; there are four different types of nucleotide in DNA.
(b) B1 DNA is a polymer made up of two strands of nucleotides, oe
(b) B1 the two strands are coiled together to form a double helix
(b) Answer: DNA is a polymer made up of two strands of nucleotides. The two strands are coiled together to form a double helix.
(c) B1 the order/sequence of nucleotide bases forms a code (the genetic code), oe
(c) B1 which determines the sequence of amino acids joined together to build a particular protein, oe
(c) Answer: The sequence of nucleotide bases along a DNA strand forms a code (the genetic code) that determines the order in which amino acids are joined together to build a particular protein.

Alcohols, Carboxylic Acids and Polymers - Worksheets, Questions and Revision