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Secondary 3 Chemistry Organic Chemistry Quiz

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Secondary 3 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 Crude Oil (Questions 1–5)

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

(b) Explain why the fraction collected at the top of the fractionating column is more flammable than the fraction collected at the bottom. [2]

2. Decane ( $C_{10}H_{22}$ ) is a hydrocarbon found in crude oil.
(a) Define the term hydrocarbon. [1]

(b) Decane can undergo cracking to produce ethene and another hydrocarbon. Write the balanced chemical equation for this reaction. [2]

3. Methane ( $CH_4$ ) and ethene ( $C_2H_4$ ) are both hydrocarbons.
(a) Describe a chemical test to distinguish between methane and ethene. Include the reagent used and the expected observation for ethene. [2]
Reagent: _______________________________________________________________
Observation with ethene: _________________________________________________
(b) Methane burns in excess oxygen. Write the balanced chemical equation for this complete combustion. [2]

4. Ethene is used to make poly(ethene).
(a) Name the type of polymerisation reaction that converts ethene into poly(ethene). [1]

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

Answer space

5. Butane ( $C_4H_{10}$ ) exists as two structural isomers.
(a) Draw the displayed formula of n-butane. [1]

Answer space

(b) Draw the displayed formula of the other isomer, 2-methylpropane (isobutane). [1]

Answer space

Section B: Alcohols, Carboxylic Acids, and Esters (Questions 6–10)

6. Ethanol ( $C_2H_5OH$ ) can be produced by two different methods.
(a) Name the process used to produce ethanol from glucose ( $C_6H_{12}O_6$ ). [1]

(b) State one condition required for this process. [1]

7. Ethanol reacts with ethanoic acid in the presence of concentrated sulfuric acid.
(a) Name the organic product formed in this reaction. [1]

(b) State the type of reaction occurring. [1]

8. Propanoic acid ( $C_2H_5COOH$ ) is a carboxylic acid.
(a) Describe the observation when propanoic acid reacts with magnesium ribbon. [1]

(b) Write the balanced chemical equation for the reaction between propanoic acid and sodium carbonate ( $Na_2CO_3$ ). [2]

9. Methanol ( $CH_3OH$ ) is the first member of the alcohol homologous series.
(a) Deduce the molecular formula of the fourth member of this series. [1]

(b) Explain what is meant by the term homologous series. [2]

10. Ethanoic acid is a weak acid.
(a) Explain what is meant by the term weak acid in terms of ionisation. [1]

(b) Suggest the approximate pH value of a dilute solution of ethanoic acid. [1]

Section C: Polymers and Macromolecules (Questions 11–15)

11. Poly(ethene) and Terylene are two different types of polymers.
(a) State which of these two polymers is a condensation polymer. [1]

(b) Identify the small molecule eliminated during the formation of Terylene. [1]

12. Nylon is a polyamide.
(a) Name the two types of functional groups that link the monomers in nylon. [1]

(b) Explain why nylon is suitable for making ropes and fishing lines. [1]

13. Disposal of plastics is an environmental issue.
(a) State one problem associated with disposing of non-biodegradable plastics in landfills. [1]

(b) Suggest one alternative method of disposing of plastics that reduces pollution, other than landfill. [1]

14. Consider the monomer chloroethene ( $C_2H_3Cl$ ).
(a) Draw the displayed formula of chloroethene. [1]

Answer space

(b) Name the polymer formed from chloroethene. [1]

15. A sample of plastic is heated. It softens and can be remoulded.
(a) State whether this plastic is a thermoplastic or a thermosetting plastic. [1]

(b) Explain this behaviour in terms of the structure of the polymer chains. [1]

Section D: Structure and Reactivity (Questions 16–20)

16. Ethene undergoes an addition reaction with steam.
(a) Name the product formed. [1]

(b) State the catalyst and temperature used in this industrial process. [2]
Catalyst: __________________________
Temperature: __________________________

17. Halogens react with alkanes in the presence of ultraviolet (UV) light.
(a) Name the type of reaction that occurs between ethane and chlorine in UV light. [1]

(b) Write the formula of one organic product formed when ethane reacts with chlorine. [1]

18. Compare the bonding in ethane and ethene.
(a) State the type of bond between carbon atoms in ethane. [1]

(b) State the type of bond between carbon atoms in ethene. [1]

19. The general formula for alkenes is $C_nH_{2n}$ .
(a) Calculate the relative molecular mass ( $M_r$ ) of propene ( $C_3H_6$ ). [1]
(Relative atomic masses: C = 12, H = 1)
Answer: __________________________
(b) Determine the empirical formula of propene. [1]

20. Biofuels are alternatives to fossil fuels.
(a) State one advantage of using bioethanol instead of petrol. [1]

(b) State one disadvantage of producing bioethanol from food crops. [1]

*** End of Quiz ***

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Answers

Secondary 3 Chemistry Quiz - Organic Chemistry (Answer Key)

Total Marks: 40

Section A: Hydrocarbons and Crude Oil

1.
(a) Boiling point (or volatility). [1]
(b) The fraction at the top has smaller molecules / shorter carbon chains. [1]
Smaller molecules have weaker intermolecular forces, making them more volatile and easier to ignite (more flammable). [1]

2.
(a) A compound containing only hydrogen and carbon atoms. [1]
(b) $C_{10}H_{22} \rightarrow C_2H_4 + C_8H_{18}$ [2]
(1 mark for correct formulas, 1 mark for balancing)
(c) To produce alkenes (for polymers) from alkanes; OR to produce shorter chain alkanes which are in higher demand (e.g., petrol). [1]

3.
(a) Reagent: Bromine water (or aqueous bromine). [1]
Observation: Bromine water changes from orange/brown to colourless (decolourises). [1]
(b) $CH_4 + 2O_2 \rightarrow CO_2 + 2H_2O$ [2]
(1 mark for correct formulas, 1 mark for balancing)

4.
(a) Addition polymerisation. [1]
(b)

\begin{bmatrix} \text{H} & \text{H} \\ | & | \\ -\text{C} & -\text{C}- \\ | & | \\ \text{H} & \text{H} \end{bmatrix}_n

[2]
(1 mark for single bond between carbons in repeat unit, 1 mark for continuation bonds extending outside brackets)

5.
(a)

\begin{array}{cccc} \text{H} & \text{H} & \text{H} & \text{H} \\ | & | & | & | \\ \text{H}-\text{C}-\text{C}-\text{C}-\text{C}-\text{H} \\ | & | & | & | \\ \text{H} & \text{H} & \text{H} & \text{H} \end{array}

[1]
(b)

\begin{array}{c} \text{H} \\ | \\ \text{H}-\text{C}-\text{H} \\ | \\ \text{H}-\text{C}-\text{H} \\ | \quad | \\ \text{H} \quad \text{C}-\text{H} \\ \quad \quad | \\ \quad \quad \text{H} \end{array} \quad \text{or} \quad \begin{array}{ccc} & \text{CH}_3 & \\ & | & \\ \text{H}_3\text{C}- & \text{CH} & -\text{CH}_3 \end{array}

(Displayed formula must show all bonds) [1]
(c) They have the same molecular formula ( $C_4H_{10}$ ) but different structural arrangements. [1]

Section B: Alcohols, Carboxylic Acids, and Esters

6.
(a) Fermentation. [1]
(b) Anaerobic conditions (no oxygen) OR Temperature around 30-40°C OR Presence of yeast. [1]
(c) $C_6H_{12}O_6 \rightarrow 2C_2H_5OH + 2CO_2$ [2]
(1 mark for correct formulas, 1 mark for balancing)

7.
(a) Ethyl ethanoate (or ethyl acetate). [1]
(b) Esterification. [1]
(c) Sweet/fruity smell. [1]

8.
(a) Effervescence / Bubbles of gas produced; Magnesium dissolves. [1]
(b) $2C_2H_5COOH + Na_2CO_3 \rightarrow 2C_2H_5COONa + H_2O + CO_2$ [2]
(1 mark for correct salt formula, 1 mark for balancing including water and carbon dioxide)

9.
(a) $C_4H_9OH$ (or $C_4H_{10}O$ ). [1]
(b) A family of compounds with:

The same general formula.
Same functional group.
Similar chemical properties.
Gradual change in physical properties.
(Any 2 points) [2]

10.
(a) It only partially ionises (dissociates) in water to produce $H^+$ ions. [1]
(b) pH 3 – 6 (Accept any value in this range). [1]

Section C: Polymers and Macromolecules

11.
(a) Terylene. [1]
(b) Water ( $H_2O$ ). [1]

12.
(a) Amide links (or peptide bonds). [1]
(b) It has high tensile strength / is strong. [1]

13.
(a) They do not rot/decompose; takes up space; produces methane gas (if anaerobic decomposition occurs slowly); leaches toxins. [1]
(b) Recycling; Incineration (with energy recovery). [1]

14.
(a)

\begin{array}{cc} \text{H} & \text{Cl} \\ | & | \\ \text{C} = & \text{C} \\ | & | \\ \text{H} & \text{H} \end{array}

[1]
(b) Poly(chloroethene) or PVC. [1]

15.
(a) Thermoplastic. [1]
(b) The polymer chains are held together by weak intermolecular forces which can be overcome by heating, allowing chains to slide over each other. [1]

Section D: Structure and Reactivity

16.
(a) Ethanol. [1]
(b) Catalyst: Phosphoric acid ( $H_3PO_4$ ). [1]
Temperature: 300°C (Accept 250-350°C). [1]

17.
(a) Substitution. [1]
(b) $C_2H_5Cl$ (Chloroethane) OR $C_2H_4Cl_2$ etc. [1]

18.
(a) Single covalent bond. [1]
(b) Double covalent bond. [1]

19.
(a) $(3 \times 12) + (6 \times 1) = 36 + 6 = 42$ . [1]
(b) $CH_2$ . [1]

20.
(a) Renewable source; Carbon neutral (plants absorb $CO_2$ grown to make fuel); Reduces reliance on fossil fuels. [1]
(b) Uses land that could be used for food production; Deforestation to clear land for crops; High water usage. [1]