Home / iGCSE Chemistry 0620 Extended – 4.2 Hydrogen–oxygen fuel cells- Exam Style Questions Paper 4
Hydrogen is the first element of the Periodic Table.
(a) Hydrogen is used in fuel cells to produce electricity in vehicles.
(i) Name the substance which combines with hydrogen in a fuel cell.
(ii) Give one advantage and one disadvantage of using fuel cells instead of gasoline in vehicle engines.
(b) Hydrogen gas can be made from petroleum by a two-step procedure.
step 1 Petroleum is separated into different components.
step 2 Large molecules obtained in step 1 are converted into smaller molecules including hydrogen gas.
(i) Name the process used in step 1.
(ii) Name the process used in step 2.
(c) Organic compounds contain hydrogen atoms.
Calculate the number of hydrogen atoms in 44.0 g of the ester methyl propanoate, CH3CH2COOCH3.
One mole of CH3CH2COOCH3 contains \(6.02 \times 10^{23}\) molecules.
Give your answer in standard form.
(d) For each of the homologous series shown, name a member that contains six hydrogen atoms.
– alkanes
– alkenes
– alcohols
– carboxylic acids
(e) Unsaturated alkenes are converted into saturated alkanes by reaction with hydrogen gas.
(i) State why alkenes and alkanes are hydrocarbons.
(ii) State why alkenes are unsaturated.
(iii) Name the catalyst needed to convert alkenes into alkanes.
(iv) Explain why the conversion of alkenes into alkanes is an addition reaction.
Most-appropriate topic codes (Cambridge IGCSE Chemistry 0620):
• Topic 4.2 — Hydrogen-oxygen fuel cells (Parts (a)(i), (a)(ii))
• Topic 11.3 — Fuels / Petroleum (Parts (b)(i), (b)(ii))
• Topic 3.3 — The mole and the Avogadro constant (Part (c))
• Topic 11.2 — Naming organic compounds / Homologous series (Part (d))
• Topic 11.5 — Alkenes / Addition reactions (Parts (e)(i) to (e)(iv))
(a)(i) Oxygen (O2). In a hydrogen fuel cell, hydrogen gas is combined with oxygen gas to produce electricity, with water as the only chemical product.
(a)(ii) Advantage: Water is the only product (no pollution / environmentally friendly). Disadvantage: Hydrogen is difficult to store (requires high pressure or low temperatures) / Fewer refuelling stations.
(b)(i) Fractional distillation. This process separates petroleum into different fractions based on their different boiling points.
(b)(ii) Cracking. This process breaks down large alkane molecules into smaller, more useful molecules (including alkenes and hydrogen) using high temperature and a catalyst.
(c) \(2.408 \times 10^{24}\) atoms.
1. Molar mass = (4×12)+(8×1)+(2×16) = 88 g/mol. Moles = 44/88 = 0.5 mol.
2. Each molecule has 8 H atoms. Moles of H atoms = 0.5 × 8 = 4.0 mol.
3. Number of atoms = 4.0 × (6.02 × 1023) = 2.408 × 1024.
(d) Alkanes: Ethane (C2H6). Alkenes: Propene (C3H6). Alcohols: Ethanol (C2H5OH). Carboxylic acids: Propanoic acid (C2H5COOH).
(e)(i) They contain only carbon and hydrogen atoms (they are compounds made of hydrogen and carbon only).
(e)(ii) They contain a carbon-carbon double bond (C=C) / they do not have the maximum number of hydrogen atoms.
(e)(iii) Nickel (Ni).
(e)(iv) Only one product is formed (the alkane) from the two reactants (alkene and hydrogen), with no other products / atoms are added across the double bond.