WJEC Chemistry for AS Level: Revision Workbook

Answers Practice questions: Unit 1: The Language of Chemistry, Structure of Matter and Simple Reactions Section 1.1: Formulae and equations Q1 (a) (i) Ba 2+ (aq) + SO 4 2− (aq) r BaSO 4 (s) 1 mark for equation. 1 mark for state symbols. (ii) Fe 2+ (aq) + 2OH − (aq) r Fe(OH) 2 (s) 1 mark for equation. 1 mark for state symbols. (b) (i) Cl 2 (g) + 2Br − (aq) r 2Cl − (aq) + Br 2 (aq) 1 mark for equation. 1 mark for state symbols. (ii) Oxidation state of chlorine goes from 0 at start to –1 at end. This is reduction as oxidation state becomes more negative (1 mark). Oxidation state of bromine goes from –1 at start to 0 at end. This is oxidation as oxidation state becomes more positive (1 mark). Q2 (a) CuCO 3 + 2CH 3 COOH r Cu(CH 3 COO) 2 + H 2 O + CO 2 (1 mark for correct formulae, 1 for balancing). (b) S 2 O 3 2− = +2; S = 0; SO 2 = +4 (1 mark for 2 correct, 2 for all 3 correct). Q3 (a) Al 2 O 3 + 3H 2 SO 4 r Al 2 (SO 4 ) 3 + 3H 2 O (1 mark for correct formulae, 1 for balancing). (b) (i) H + (aq) + OH − (aq) r H 2 O (l). (ii) Al 3+ (aq) + 3OH – (aq) r Al(OH) 3 (s). Q4 (a) 6PbO + O 2 r 2Pb 3 O 4 (1 mark for correct formulae, 1 mark for balancing). (b) Oxidation state of lead at the start = +2, at end = +2.67 (1 mark, accept fractions or any rounded number with at least one decimal place) (1). Oxidation state of lead has become more positive so has been oxidised (1). Section 1.2: Basic ideas about atoms Q1 Nitrogen or any other group 5 element. Q2 1s 2 2s 2 2p 6 Q3 ɐ ɐ ɐ ɐ Ȝ Ȝ Ȝ Ȝ Ȝ Ȝ 3s 3p 3d 4s Q4 Q5 Group 4 (1) as the most significant increase is between the 4th and 5th ionisation (1). Q6 (a) Both processes involve electrons which have very little mass / Mass number only affected by loss or gain of protons or neutrons. (b) As, Kr Q7 233, Am (1); 229, Pu (1). Q8 (a) (2 for all three columns correct, 1 for two columns correct). Ƚ Ⱦ g positron Change in atomic number –2 +1 0 –1 Change in mass number –4 0 0 0 z y x 172 | WJEC Chemistry for AS Level: Revision Workbook | Answers