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GCSE ChemistryAQA, Edexcel and OCR

Organic chemistry: GCSE questions with answers

20 chemistry questions on organic chemistry. Pick your answer, then tap to see if you were right and why. Every answer comes from the Show Working science bank, checked against the GCSE content every board in England teaches.

Quiz yourself: 20 questions 1 6-mark question

01 / Quiz yourselfTry it, then tap to check

Organic chemistry questions to try

Choose your answer before you open it. Then read why, so it sticks.

01 / Organic chemistryBoth tiers · separate only

What is a homologous series?

  1. AA family with the same functional group
  2. BCompounds made only of hydrogen and carbon
  3. CCompounds with the same molecular formula
  4. DCompounds with the same boiling point
Show the answer

Answer: A A family with the same functional group

A homologous series is a family of compounds with the same functional group and the same general formula. Each member differs from the next by CH₂. They have similar reactions, and their physical properties, such as boiling point, change gradually.

Checked against Pearson Edexcel GCSE Chemistry (1CH0) specification, statement 9.32C

02 / Organic chemistryBoth tiers · separate only

Which functional group do all alcohols contain?

  1. A–COOH
  2. BC=C
  3. C–OH
  4. DOH⁻ ion
Show the answer

Answer: C –OH

A functional group is the part of a molecule that decides how it reacts. Alkenes have a C=C double bond, alcohols have –OH and carboxylic acids have –COOH. The –OH in an alcohol is bonded to a carbon atom; it is not a hydroxide ion.

Checked against AQA GCSE Chemistry (8462) specification, section 4.7.2.2 to 4.7.2.4

03 / Organic chemistryBoth tiers · separate only

Which of these is an alkene?

  1. AC₂H₅OH
  2. BCH₃COOH
  3. CC₃H₆
  4. DC₃H₈
Show the answer

Answer: C C₃H₆

You can recognise each series from its formula. Alkanes are CₙH₂ₙ₊₂, alkenes CₙH₂ₙ, alcohols end in OH and carboxylic acids end in COOH. So C₃H₆ is propene, an alkene, and C₂H₅COOH is propanoic acid.

Checked against AQA GCSE Chemistry (8462) specification, section 4.7.2.1

04 / Organic chemistryBoth tiers · separate only

Why are alkenes described as unsaturated?

  1. AThey have a C=C double bond
  2. BThey have only C–C single bonds
  3. CThey contain an –OH group
  4. DThey contain oxygen atoms
Show the answer

Answer: A They have a C=C double bond

Alkenes have a C=C double bond, so they could hold more hydrogen atoms: they are unsaturated. Bromine adds across the double bond, so orange bromine water turns colourless. Alkanes have only single bonds, so the bromine water stays orange.

Checked against Royal Society of Chemistry, Microscale simple cracking

05 / Organic chemistryBoth tiers · separate only

What is the formula of propane?

  1. AC₃H₇OH
  2. BC₃H₆
  3. CC₃H₈
  4. DC₃H₁₀
Show the answer

Answer: C C₃H₈

The start of each name shows the number of carbon atoms: meth- 1, eth- 2, prop- 3, but- 4. The first four alkanes are methane CH₄, ethane C₂H₆, propane C₃H₈ and butane C₄H₁₀.

Checked against Pearson Edexcel GCSE Chemistry (1CH0) specification, statement 9.10C

06 / Organic chemistryBoth tiers · separate only

Which alkene has three carbon atoms?

  1. AButene
  2. BEthene
  3. CPropane
  4. DPropene
Show the answer

Answer: D Propene

The first alkenes are ethene C₂H₄, propene C₃H₆ and butene C₄H₈. Each has a C=C double bond, which needs two carbon atoms, so the series starts at ethene. An alkene has two fewer hydrogen atoms than the alkane with the same number of carbons.

Checked against AQA GCSE Chemistry (8462) specification, section 4.7.2.1

07 / Organic chemistryBoth tiers · separate only

What is the formula of ethanol?

  1. AC₂H₅OH
  2. BCH₃COOH
  3. CC₂H₄
  4. DC₂H₆
Show the answer

Answer: A C₂H₅OH

The first four alcohols are methanol CH₃OH, ethanol C₂H₅OH, propanol C₃H₇OH and butanol C₄H₉OH. Their names end in -ol, and each has an –OH group in place of one hydrogen atom of the alkane.

Checked against AQA GCSE Chemistry (8462) specification, section 4.7.2.3

08 / Organic chemistryBoth tiers · separate only

What is the formula of ethanoic acid?

  1. AC₂H₅OH
  2. BCH₃COOH
  3. CHCOOH
  4. DC₂H₅COOH
Show the answer

Answer: B CH₃COOH

The first four carboxylic acids are methanoic acid HCOOH, ethanoic acid CH₃COOH, propanoic acid C₂H₅COOH and butanoic acid C₃H₇COOH. The carbon in the –COOH group counts, so ethanoic acid has two carbon atoms.

Checked against AQA GCSE Chemistry (8462) specification, section 4.7.2.4

09 / Organic chemistryBoth tiers · separate only

In a displayed formula, how many bonds does each carbon atom have?

  1. AOne
  2. BTwo
  3. CFour
  4. DThree
Show the answer

Answer: C Four

A displayed formula shows every atom and every bond as a line. Carbon always makes four bonds, hydrogen one and oxygen two. A C=C double bond is drawn as two lines, and in an alcohol the oxygen sits between a carbon and a hydrogen: C–O–H.

Checked against OpenStax Chemistry 2e, 20.2 Alcohols and Ethers

10 / Organic chemistryBoth tiers · separate only

What are the products when ethanol burns completely in air?

  1. ACarbon monoxide and water
  2. BEthanoic acid and water
  3. CCarbon dioxide and water
  4. DCarbon and hydrogen
Show the answer

Answer: C Carbon dioxide and water

Alkanes, alkenes and alcohols all burn completely in plenty of oxygen to give carbon dioxide and water. Alkenes often burn with a smoky flame because some of the combustion is incomplete, giving soot (carbon) and carbon monoxide.

Checked against AQA GCSE Chemistry (8462) specification, section 4.7.2.2

11 / Organic chemistryBoth tiers · separate only

What forms when ethene reacts with hydrogen?

  1. APoly(ethene)
  2. BEthanol
  3. CEthane
  4. DPropane
Show the answer

Answer: C Ethane

In an addition reaction, atoms add across the C=C double bond, which becomes a single bond. Ethene + hydrogen → ethane, and ethene + bromine → C₂H₄Br₂, with one bromine atom on each carbon. Other alkenes react in the same way.

Checked against AQA GCSE Chemistry (8462) specification, section 4.7.2.2

12 / Organic chemistryBoth tiers · separate only

What does ethanol form when it is oxidised?

  1. AEthane
  2. BEthene
  3. CEthanoic acid
  4. DButanoic acid
Show the answer

Answer: C Ethanoic acid

An oxidising agent turns an alcohol into the carboxylic acid with the same number of carbon atoms: ethanol gives ethanoic acid. This is also why wine left open to the air turns sour, as microbes oxidise the ethanol to ethanoic acid (vinegar).

Checked against Pearson Edexcel GCSE Chemistry (1CH0) specification, statement 9.31C

13 / Organic chemistryBoth tiers · separate only

Why do ethene and butene react in the same way with bromine?

  1. AThey have the same number of carbons
  2. BThey have the same boiling point
  3. CThey have the same relative formula mass
  4. DThey have the same functional group
Show the answer

Answer: D They have the same functional group

Reactions depend on the functional group, not on the length of the carbon chain. All alkenes decolourise bromine water, and carboxylic acids react like other acids, fizzing with carbonates to give carbon dioxide. So you can predict reactions of members you have not met.

Checked against Pearson Edexcel GCSE Chemistry (1CH0) specification, statement 9.30C and 9.32C

14 / Organic chemistryBoth tiers · separate only

What must a monomer have to take part in addition polymerisation?

  1. AAn –OH group
  2. BOnly single bonds
  3. CA –COOH group
  4. DA C=C double bond
Show the answer

Answer: D A C=C double bond

In addition polymerisation, many small alkene molecules (monomers) join into a long chain (a polymer) by opening their C=C double bonds. Nothing else is made, so the repeating unit contains exactly the same atoms as the monomer.

Checked against AQA GCSE Chemistry (8462) specification, section 4.7.3.1

15 / Organic chemistryBoth tiers · separate only

How do the atoms in the repeating unit of an addition polymer compare with the monomer?

  1. AThe unit has two fewer hydrogens
  2. BThe unit has an extra oxygen atom
  3. CThey are the same atoms
  4. DThe unit has half the atoms
Show the answer

Answer: C They are the same atoms

When the polymer forms, each C=C opens up to a single bond and links to the next unit. So the repeating unit has the same atoms as the monomer, but only single bonds between its carbons, with a bond at each end joining it to the next unit.

Checked against AQA GCSE Chemistry (8462) specification, section 4.7.3.1

16 / Organic chemistryBoth tiers · separate only

A polymer has the repeating unit –CH₂–CHCl–. Which monomer was used?

  1. ACH₂=CHCl
  2. BCH₂=CH₂
  3. CCHCl=CHCl
  4. DCH₃–CH₂Cl
Show the answer

Answer: A CH₂=CHCl

To find the polymer, open the C=C bond of the monomer into a single bond and add a bond at each end. To find the monomer, put a C=C back between the two carbons of the repeating unit. Other atoms or groups on the carbons, such as Cl or CH₃, stay where they are.

Checked against Pearson Edexcel GCSE Chemistry (1CH0) specification, statement 9.20C

17 / Organic chemistryHigher only · separate only

Besides the polymer, what else forms in condensation polymerisation?

  1. AA large molecule such as starch
  2. BHydrogen gas only
  3. CNothing else forms
  4. DA small molecule such as water
Show the answer

Answer: D A small molecule such as water

In condensation polymerisation, monomers with two functional groups each (one at each end) react, and a small molecule such as water is given off every time a link forms. With a group at each end, the chain can keep growing in both directions.

Checked against AQA GCSE Chemistry (8462) specification, section 4.7.3.2

18 / Organic chemistryHigher only · separate only

Which pair of monomers can react to make a polyester?

  1. AA diol and a dicarboxylic acid
  2. BAn alkane and an alcohol
  3. CTwo alkenes with C=C double bonds
  4. DAn alkene and a molecule of steam
Show the answer

Answer: A A diol and a dicarboxylic acid

A diol has two –OH groups and a dicarboxylic acid has two –COOH groups. An –OH on one monomer reacts with a –COOH on the other to make an ester link, giving off one water molecule each time. Repeating this builds a long chain whose repeating unit holds one part from each monomer.

Checked against AQA GCSE Chemistry (8462) specification, section 4.7.3.2

19 / Organic chemistryBoth tiers · separate only

What are the monomers that make up DNA called?

  1. AAmino acids
  2. BNucleotides
  3. CBases
  4. DGlucose units
Show the answer

Answer: B Nucleotides

DNA is a natural polymer made from four different monomers called nucleotides. Most DNA molecules are two polymer chains twisted into a double helix. The order of the nucleotides carries the genetic instructions.

Checked against AQA GCSE Chemistry (8462) specification, section 4.7.3.4

20 / Organic chemistryBoth tiers · separate only

Proteins are polymers made from which monomers?

  1. AAmino acids
  2. BFatty acids
  3. CNucleotides
  4. DSugars
Show the answer

Answer: A Amino acids

Many important polymers are made by living things. Proteins are built from amino acids. Starch and cellulose are both built from sugar (glucose) units. DNA is built from nucleotides.

Checked against AQA GCSE Chemistry (8462) specification, section 4.7.3.4

02 / Longer answersMarked by levels

6-mark questions on this topic

Write your answer first, on paper. Then open it and tick off the points you made. How 6-mark questions are marked.

6 marks / Addition and condensation polymers comparedHigher only · separate only

Poly(ethene) is made by addition polymerisation. A polyester is made by condensation polymerisation from a monomer with two carboxylic acid groups and a monomer with two alcohol (-OH) groups.

Compare addition polymerisation and condensation polymerisation.

What a full answer includes
  • In both, many small monomer molecules join to make one very long polymer molecule.
  • Addition polymers are made from monomers that contain a C=C double bond, such as ethene.
  • In addition polymerisation the double bond opens and the monomers join, with no other product.
  • So the repeating unit has the same atoms as the monomer.
  • Condensation polymers are made from monomers that each have two functional groups, such as two -COOH or two -OH groups.
  • Often two different monomers are used, joining alternately.
  • Each time two monomers join, a small molecule such as water is also formed.
  • So the repeating unit has fewer atoms than the monomers that made it.

Model answer

In both types of polymerisation, many small molecules called monomers join together to form one very long molecule, a polymer, made of repeating units. In addition polymerisation, the monomers are alkenes, such as ethene, which contain a carbon to carbon double bond. The double bond opens up and the monomers join to each other in a long chain. Nothing else is formed, so the polymer is the only product and the repeating unit contains exactly the same atoms as the monomer. In condensation polymerisation, each monomer must have two functional groups, one at each end. For a polyester, two different monomers are used: one with two carboxylic acid groups and one with two alcohol groups, and they join alternately. Each time a carboxylic acid group reacts with an alcohol group to form an ester link, a small molecule, water, is also formed. So condensation polymerisation gives two products, the polymer and water, and the repeating unit has fewer atoms than the two monomers it came from. The key differences are the functional groups needed and whether a small molecule is lost.

Where marks slip

Keeping the C=C double bond in the addition polymer, or forgetting that a small molecule is lost in condensation, are the usual slips. Every comparison point should state what each type does.

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