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O Level Chemistry Organic Chemistry Quiz

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Questions

O-Level Chemistry Quiz - Organic Chemistry

Name: __________________________
Class: __________________________
Date: __________________________
Score: ________ / 40

Duration: 45 minutes
Total Marks: 40

Instructions:

Answer all questions.
Write your answers in the spaces provided.
The number of marks is given in brackets [ ] at the end of each question or part question.
You may use a periodic table and a calculator.

Section A: Hydrocarbons and Fuels (Questions 1–5)

1. Crude oil is a mixture of hydrocarbons that is separated into fractions by fractional distillation. (a) State the physical property on which the separation of crude oil fractions depends. [1]

(b) Explain why the fraction collected at the top of the fractionating column has a lower boiling point than the fraction collected at the bottom. [2]

2. The table below shows information about two hydrocarbons, A and B.

Hydrocarbon	Molecular Formula	Type of Hydrocarbon
A	$C_6H_{14}$	Alkane
B	$C_6H_{12}$	Alkene

(a) Hydrocarbon A is hexane. Draw the structural formula of a branched isomer of hexane. [1]

(b) Describe a simple chemical test to distinguish between hydrocarbon A and hydrocarbon B. Include the reagent used and the expected observations for both. [3] Reagent: _________________________________________________________ Observation with A: ________________________________________________ Observation with B: ________________________________________________

3. Ethene ( $C_2H_4$ ) is an important industrial chemical. (a) Ethene is produced by cracking long-chain alkanes. State one condition required for cracking. [1]

(b) Complete the equation for the cracking of decane ( $C_{10}H_{22}$ ) to produce ethene and one other alkane. [1] $C_{10}H_{22} \rightarrow C_2H_4 + \text{__________________}$

4. Methane is the main component of natural gas. (a) Write the balanced chemical equation for the complete combustion of methane. [2]

(b) Explain why incomplete combustion of methane is dangerous in a poorly ventilated room. [2]

5. Bioethanol is considered a renewable fuel, whereas ethanol produced from ethene is not. (a) Name the process used to produce ethanol from glucose. [1]

(b) State one advantage of using bioethanol as a fuel compared to petrol. [1]

Section B: Alcohols, Acids, and Esters (Questions 6–12)

6. Ethanol can be oxidised to ethanoic acid. (a) Name a suitable oxidising agent for this reaction. [1]

(b) State the colour change observed when acidified potassium manganate(VII) is used as the oxidising agent. [1] From ____________________ to ____________________

7. Ethanoic acid is a weak acid. (a) Define the term weak acid. [1]

(b) Write the ionic equation for the reaction between ethanoic acid and aqueous sodium hydroxide. [2]

8. A student reacts propanol with propanoic acid in the presence of concentrated sulfuric acid. (a) Name the type of reaction occurring. [1]

(b) Draw the structural formula of the organic product formed. [2]

9. The table below shows the pH of 0.1 mol/dm³ solutions of hydrochloric acid and ethanoic acid.

Acid	pH
Hydrochloric acid	1.0
Ethanoic acid	2.9

Explain, in terms of particles, why the pH of ethanoic acid is higher than that of hydrochloric acid, even though their concentrations are the same. [2]

10. Esters are used as flavourings and solvents. (a) Name the ester formed from ethanol and butanoic acid. [1]

(b) Draw the structural formula of methyl ethanoate. [2]

11. Butanoic acid reacts with magnesium ribbon. (a) Write the balanced chemical equation for this reaction. [2]

(b) Describe one observation during this reaction. [1]

12. A sample of ethanol contains a small amount of water. (a) Name a suitable drying agent that can be used to remove water from ethanol. [1]

(b) Why can’t calcium oxide be used to dry ethanoic acid? [1]

Section C: Polymers and Macromolecules (Questions 13–20)

13. Poly(ethene) is an addition polymer. (a) Draw the structure of the monomer used to make poly(ethene). [1]

(b) Draw the repeating unit of poly(ethene). [2]

14. Nylon is a condensation polymer. (a) Identify the two functional groups present in the monomers used to make nylon. [2]

(b) Name the small molecule eliminated when nylon is formed. [1]

15. Terylene is another condensation polymer. (a) Terylene is a polyester. What type of linkage joins the monomers in Terylene? [1]

(b) Suggest one reason why poly(ethene) is preferred over Terylene for making plastic bags. [1]

16. Disposal of plastics causes environmental problems. (a) Explain why addition polymers like poly(ethene) are non-biodegradable. [2]

(b) State one method of disposing of waste plastics other than landfill. [1]

17. The structure of a section of a polymer is shown below:

$\dots -[CH_2-CH(CH_3)]_n- \dots$

(a) Draw the structure of the monomer. [2]

(b) Name this polymer. [1]

18. Compare the structures of diamond and graphite. (a) Explain why graphite conducts electricity but diamond does not. [2]

(b) Explain why diamond is very hard. [2]

19. A student is given two white solids: starch and poly(ethene). Describe a chemical test to distinguish between them. [2] Reagent: _________________________________________________________ Observation with Starch: ___________________________________________ Observation with Poly(ethene): ______________________________________

20. Proteins are natural polymers. (a) Name the monomers that make up proteins. [1]

(b) What type of polymerisation forms proteins? [1]

*** End of Quiz ***

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Answers

O-Level Chemistry Quiz - Organic Chemistry (Answer Key)

Total Marks: 40

Section A: Hydrocarbons and Fuels

1. (a) Boiling point [1] (b)

Fractions at the top have smaller molecules / shorter carbon chains [1].
Smaller molecules have weaker intermolecular forces / van der Waals forces, requiring less energy to overcome [1].

2. (a) Any correct branched isomer of $C_6H_{14}$ (e.g., 2-methylpentane or 2,2-dimethylbutane). Must show all bonds or correct condensed structure. [1] (b)

Reagent: Aqueous bromine / Bromine water [1].
Observation with A (Alkane): No change / Remains orange-brown [1].
Observation with B (Alkene): Decolourises / Turns colourless [1]. (Note: If KMnO4 is used, accept: Purple to colourless for B, no change for A).

3. (a) High temperature / Heat / Catalyst (e.g., aluminium oxide) [1]. (b) $C_8H_{18}$ [1].

4. (a) $CH_4 + 2O_2 \rightarrow CO_2 + 2H_2O$ [2] (1 for correct formulae, 1 for balancing). (b)

Incomplete combustion produces carbon monoxide (CO) [1].
CO is toxic/poisonous because it binds to haemoglobin, preventing oxygen transport [1].

5. (a) Fermentation [1]. (b) Renewable source / Carbon neutral (absorbs CO2 during growth) / Reduces reliance on crude oil [1].

Section B: Alcohols, Acids, and Esters

6. (a) Acidified potassium manganate(VII) / Acidified potassium dichromate(VI) [1]. (b) Purple to colourless (if manganate) OR Orange to green (if dichromate) [1].

7. (a) An acid that only partially ionises/dissociates in water [1]. (b) $CH_3COOH + OH^- \rightarrow CH_3COO^- + H_2O$ [2] (1 for correct products, 1 for balancing/charges). Note: Ionic equation required.

8. (a) Esterification [1]. (b) Propyl propanoate structure: $CH_3CH_2COOCH_2CH_2CH_3$ [2] (1 for correct ester linkage, 1 for correct alkyl groups). (c) Catalyst [1].

Ethanoic acid is a weak acid and only partially ionises, producing a lower concentration of $H^+$ ions [1].
Hydrochloric acid is a strong acid and fully ionises, producing a higher concentration of $H^+$ ions [1].

10. (a) Ethyl butanoate [1]. (b) $CH_3COOCH_3$ [2] (1 for correct linkage, 1 for correct methyl/ethanoate groups).

11. (a) $2CH_3CH_2CH_2COOH + Mg \rightarrow (CH_3CH_2CH_2COO)_2Mg + H_2$ [2] (1 for correct salt formula, 1 for balancing/H2). (b) Effervescence / Bubbles / Magnesium dissolves [1].

12. (a) Anhydrous calcium chloride / Fused calcium chloride [1]. (Note: Do not accept Calcium Oxide or Conc H2SO4 for ethanol drying in all contexts, but CaCl2 is standard for neutral organics. Conc H2SO4 reacts with ethanol). (b) Calcium oxide is a base and will react with ethanoic acid (neutralisation) [1].

Section C: Polymers and Macromolecules

13. (a) Ethene: $CH_2=CH_2$ [1]. (b) Repeating unit: $-[CH_2-CH_2]_n-$ with bonds extending outside brackets [2] (1 for structure, 1 for brackets/bonds).

14. (a) Amine group ( $-NH_2$ ) and Carboxyl group ( $-COOH$ ) [2]. (b) Water ( $H_2O$ ) [1].

15. (a) Ester linkage [1]. (b) Poly(ethene) is cheaper / more flexible / waterproof / easier to manufacture [1].

16. (a) They have strong covalent bonds / non-polar C-C and C-H bonds that are not easily broken by microorganisms/enzymes [2]. (b) Recycling / Incineration (with energy recovery) / Cracking [1].

17. (a) Propene: $CH_2=CH(CH_3)$ [2] (1 for double bond, 1 for methyl group position). (b) Poly(propene) [1].

18. (a) Graphite has delocalised electrons between layers that can move and carry charge [1]. Diamond has no delocalised electrons; all electrons are involved in covalent bonds [1]. (b) Diamond has a giant covalent structure with strong covalent bonds in all directions [1]. Much energy is required to break these bonds [1].

19.

Reagent: Iodine solution [1].
Observation with Starch: Turns blue-black [0.5].
Observation with Poly(ethene): No change / Remains brown-orange [0.5]. (Alternative: Hydrolysis followed by Benedict's test, but Iodine is direct).

20. (a) Amino acids [1]. (b) Condensation polymerisation [1].