Chemistry questions, chapter 2

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Carbon compound

46 marks. Use Practice to check each answer as you go, or Exam to answer everything against the clock first.

Section A: objective questions

12 marks

Choose the best answer for each question.

Question 1

Which compound is an organic compound?

Carbon dioxide, CO₂
Calcium carbonate, CaCO₃
Glucose, C₆H₁₂O₆
Potassium cyanide, KCN

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Organic compounds come from living things and contain carbon covalently bonded to elements such as hydrogen, nitrogen, sulphur and phosphorus. Oxides of carbon, carbonates and cyanides are inorganic carbon compounds.

For the teacher: Remembering, low difficulty, standard 2.1.1

Textbook p. 64

Question 2

Why can petroleum be separated into fractions by fractional distillation?

The fractions have different colours
The fractions dissolve differently in water
All the fractions have the same boiling point
Each fraction has its own boiling point because of its molecular size

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The hydrocarbons in petroleum have different sizes, so each fraction vaporises and condenses at its own boiling point (textbook p. 66).

For the teacher: Understanding, low difficulty, standard 2.1.2

Textbook p. 66

Question 3

Diagram 1 shows the fractional distillation of petroleum. How does the fraction collected at the bottom of the tower compare with petrol?

Fractional distillation tower with the fractions from petroleum gas at the top to bitumen at the bottom — Diagram 1 (textbook Figure 2.2)

It has a higher boiling point and is more viscous
It has smaller molecules and burns more easily
It is lighter in colour
It contains only C₁ to C₄ molecules

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The bottom fraction (bitumen) has the biggest molecules, so a high boiling point, dark colour, high viscosity and low combustibility.

For the teacher: Analysing, medium difficulty, standard 2.1.2

Textbook p. 67

Question 4

Cracking of a long-chain hydrocarbon is shown below.
C₁₂H₂₆ → C₈H₁₈ + X
What is X?

C₄H₁₀
C₄H₈
C₃H₆
C₂H₄

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Balance the atoms: C = 12 − 8 = 4 and H = 26 − 18 = 8, so X is C₄H₈, an alkene.

For the teacher: Applying, low difficulty, standard 2.1.2

Textbook p. 68

Question 5

The boiling points of the alkanes increase from methane to hexane. What is the reason?

The van der Waals forces between molecules become stronger as the molecules get bigger
The covalent bonds in the molecules become stronger
The molecules become more reactive
The molecules become ionic

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Bigger molecules have stronger van der Waals forces between them, so more heat energy is needed to overcome the forces. Covalent bonds inside the molecules are not broken when a simple molecular substance boils.

For the teacher: Understanding, low difficulty, standard 2.2.3

Textbook p. 78

Question 6

How many moles of oxygen are needed for the complete combustion of 1 mol of propane, C₃H₈?

3 mol
4 mol
5 mol
7 mol

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C₃H₈ + 5O₂ → 3CO₂ + 4H₂O. Oxygen atoms needed = 3 × 2 + 4 = 10, so 5 mol O₂.

For the teacher: Applying, medium difficulty, standard 2.3.1

Textbook p. 80

Question 7

A gas decolourises the brown colour of bromine water. Which gas could it be?

Ethane
Propene
Methane
Propane

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Only an unsaturated hydrocarbon (alkene) with a C=C double bond decolourises bromine water by an addition reaction. Propene is an alkene; the others are alkanes.

For the teacher: Understanding, low difficulty, standard 2.3.1

Textbook p. 87

Question 8

What is the percentage of carbon by mass in propene, C₃H₆? [Relative atomic mass: H = 1, C = 12]

75.00%
81.82%
83.72%
85.71%

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36 ÷ (36 + 6) × 100 = 85.71%. (81.82% is propane, C₃H₈.)

For the teacher: Applying, medium difficulty, standard 2.3.1

Textbook p. 87

Question 9

Ethanol is heated with acidified potassium dichromate(VI) solution. What is observed and what is the product?

The orange solution turns green; ethanoic acid is formed
The orange solution turns green; ethene is formed
The purple solution turns colourless; ethanoic acid is formed
The green solution turns orange; ethanoic acid is formed

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Acidified K₂Cr₂O₇ is an oxidising agent that is reduced from orange to green. Ethanol is oxidised to ethanoic acid.

For the teacher: Applying, low difficulty, standard 2.3.1

Textbook p. 91

Question 10

Propanoic acid reacts with methanol in the presence of concentrated sulphuric acid. What is the name of the ester formed?

Propyl methanoate
Methyl ethanoate
Methyl propanoate
Methanyl propanoate

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The first part of the name comes from the alcohol (methanol gives methyl) and the second part from the acid (propanoic acid gives propanoate): methyl propanoate.

For the teacher: Applying, low difficulty, standard 2.3.2

Textbook p. 98

Question 11

Diagram 2 shows the structural formulae of three hydrocarbons, P, Q and R. Which pair are isomers?

P: four carbon atoms in a straight chain with only single bonds — P

Q: three carbon atoms in a chain with a methyl branch on the middle carbon — P

P and R
P and Q
Q and R
P, Q and R

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P is butane and Q is 2-methylpropane. Both are C₄H₁₀ with different structures (chain isomers). R is pentane, C₅H₁₂.

For the teacher: Analysing, high difficulty, standard 2.4.1

Textbook p. 101

Question 12

Which is a use of methanoic acid?

As a food flavouring
As a solvent for paint
As a fuel mixed with petrol
To coagulate latex in the rubber industry

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Methanoic acid is used in the rubber industry to coagulate latex.

For the teacher: Remembering, low difficulty, standard 2.4.3

Textbook p. 108

Section B: structured questions

34 marks

Answer all questions. Write your answers in the spaces provided.

Question 13

Petroleum is a mixture of hydrocarbons that must be refined before use.

[1 mark] (a)Name the process used to separate petroleum into its fractions.

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Fractional distillation1

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[1 mark] (b)Diesel oil and petrol are two fractions of petroleum. Which one is more viscous?

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Diesel oil (it has bigger molecules)1

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[1 mark] (c)What is meant by cracking?

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The breaking of long-chain hydrocarbons into smaller (shorter) hydrocarbon molecules at high temperature using a catalyst1

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For the teacher: Understanding, low difficulty, standard 2.1.2

Textbook p. 66

Question 14

Compound P is propane, C₃H₈, and compound Q is propene, C₃H₆. [Relative atomic mass: H = 1, C = 12]

[2 marks] (a)Calculate the percentage of carbon by mass in P and in Q.

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P: 36 ÷ 44 × 100 = 81.82%1
Q: 36 ÷ 42 × 100 = 85.71%1

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[2 marks] (b)Both burn in air. Which compound burns with the sootier flame? Explain your answer.

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Q (propene)1
Percentage of carbon by mass is higher in Q, so more carbon (soot) is formed1

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[2 marks] (c)Describe a chemical test to distinguish P from Q.

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Add bromine water (or acidified potassium manganate(VII)) to each compound and shake1
Q decolourises the brown bromine water; P shows no change1

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For the teacher: Analysing, medium difficulty, standard 2.3.1

Textbook p. 87

Question 15

Ethanol, C₂H₅OH, can be prepared in two ways.

[2 marks] (a)Write the balanced chemical equation for the fermentation of glucose, C₆H₁₂O₆.

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Correct formulae: C₆H₁₂O₆ → C₂H₅OH + CO₂1
Balanced: C₆H₁₂O₆ → 2C₂H₅OH + 2CO₂1

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[1 mark] (b)Name the enzyme in yeast that catalyses the fermentation.

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Zymase1

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[2 marks] (c)Ethanol is heated with acidified potassium dichromate(VI) solution. State the colour change and name the product formed.

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Orange to green1
Ethanoic acid1

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[1 mark] (d)Write the equation for the dehydration of ethanol.

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C₂H₅OH → C₂H₄ + H₂O1

Ethanol vapour is passed over hot porcelain chips or alumina.

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For the teacher: Applying, low difficulty, standard 2.3.1

Textbook p. 96

Question 16

Ethanoic acid reacts with propan-1-ol, C₃H₇OH, to form an ester.

[1 mark] (a)Name this type of reaction.

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Esterification1

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[1 mark] (b)Name the ester formed.

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Propyl ethanoate1

Propan-1-ol gives propyl; ethanoic acid gives ethanoate.

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[2 marks] (c)Write the chemical equation for the reaction.

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Correct formulae of reactants and products1
CH₃COOH + C₃H₇OH → CH₃COOC₃H₇ + H₂O (balanced)1

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[2 marks] (d)State two physical properties of the ester.

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Sweet / fruity smell1
Colourless liquid / insoluble in water / less dense than water / easily vaporised1

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For the teacher: Applying, low difficulty, standard 2.3.2

Textbook p. 98

Question 17

Diagram 3 shows the structural formula of an alkene.

Structural formula of an alkene with a double bond at one end of a four-carbon chain and a methyl branch on the second carbon — Diagram 3

[1 mark] (a)State the molecular formula of the compound.

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C₅H₁₀1

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[2 marks] (b)Name the compound using IUPAC nomenclature.

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Root name and suffix: but-1-ene1
Branch and position: 2-methyl; 2-methylbut-1-ene1

The longest chain containing C=C has 4 carbons; the double bond is on C1 and a methyl group is on C2.

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[1 mark] (c)But-1-ene and but-2-ene have the same molecular formula. What type of isomerism do they show?

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Position isomerism (the double bond is on a different carbon)1

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[2 marks] (d)Name the two isomers of C₄H₁₀.

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Butane1
2-methylpropane1

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For the teacher: Applying, medium difficulty, standard 2.4.2

Textbook p. 104

Question 18

Ethanol is used in hand sanitisers and, mixed with petrol, as the fuel gasohol.

[2 marks] (a)State two properties of ethanol that make it suitable for use in a hand sanitiser.

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Antiseptic (kills germs)1
Volatile (evaporates quickly) / good organic solvent / miscible with water1

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[2 marks] (b)Justify why ethanol made by fermentation of sugar cane is a better fuel to mix with petrol than using petrol alone.

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It is renewable, made from biomass, while petroleum will run out1
It burns completely with a clean flame without soot, releasing much heat1

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For the teacher: Evaluating, medium difficulty, standard 2.4.3

Textbook p. 107

Question 19

Hexane, C₆H₁₄, and hexene, C₆H₁₂, are two colourless liquids. Design a simple experiment to find out which is which.

[3 marks] (a)Describe your experiment, including the reagent, the procedure and the expected result.

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Reagent: bromine water (or acidified potassium manganate(VII) solution)1
Procedure: add 2 to 3 drops of the reagent to 2 cm³ of each liquid in separate test tubes and shake1
Result: the liquid that decolourises the reagent is hexene; the liquid that shows no change is hexane1

Tick each point you got.

For the teacher: Creating, high difficulty, standard 2.3.1

Textbook p. 86

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