Chem S3 EOY 2023 HYSS ans

3E Pure Chem SR P1 MS 2023 Q1 B Q2 D Q3 B Q4 A Q5 B Q6 B Q7 A Q8 D Q9 D Q10 C Q11 C Q12 A Q13 A Q14 A Q15 A Q16 A Q17 C Q18 C Q19 D Q20 A

3E SR Chemistry Paper 2 2023 Mark scheme 1 (a) The mistake is in methane. The lower the relative molecular mass of the gas, the faster the rate of diffusion. In the data, methane has a lower molecular mass than CO/ nitrogen. It should diffuse faster in less than 32 s, but the data showed that it diffused in 35 s. R: quicker time [1] [1] (b) Ammonia is soluble in water. [1] (c) The molecules are closely packed in a disorderly/irregular manner; and will slide across one another. [1] [1] Total: 5 2 (a) (i) Ethanol [1] (ii) • To ensure that the condenser is fully filled with water • for more efficient cooling of the vapour into liquid • for the vapour to fully condense into liquid before leaving the condenser. [1] (iii) To measure the temperature of the vapour entering the condenser / boiling point of T (so that its identity can be determined) [1] (iv) [2] (v) No. Water and oil are immisible. [1] (b) They have a simple molecular structure (A: simple molecules); with weak intermolecular forces of attraction. Hence, little/ small amount of energy is required to overcome these forces of attraction. R: ‘break’/ if wrong type of bonds are used [1] [1] Total: 8 3 (a) element atomic number number of protons number of neutrons mass number electronic configuration W 16 16 16 32 2, 8, 6 X 7 7 7 14 2, 5 Y 2 2 2 4 2 Z 11 11 12 23 2,8,1 [2] 3 right = 2M 2 right = 1M 1 right = 0M 1M - shape of graph 1M – labelling of temperature at 78 and 188 °C R: if unit is indicated on y-axis or graph goes beyond 188 °C

(b) Element Z. The atom of Z has only one valence electron. Accept: It loses one valence electron to form a complete valence electron shell. Accept: It loses electron to form a cation. [1] [1] (c) W has an electronic configuration of 2,8,6 gains 2 electrons to form an ion of W2- with a stable electronic configuration of 2, 8, 8. [1] Total:5 4 (a) (i) Zn (s)+ 2HCl (aq) → ZnCl2 (aq) + H2 (g) 1M for balanced chemical eqn THEN 1M for state symbols [2] (ii) Zn + 2H+ → Zn2+ + H2 [1] (b) Hydrogen gas is less dense than air , therefore it will not sink/ escape into the gas jar. [1] (c) Dry agent / dry the gas A: absorb moisture [1] (d) Observation: Less effervescence/bubbles observed Explanation: Ethanoic acid is a weak acid which ionise partially; Has lower H+ concentration/ lesser H+ ions(present per unit time/volume) compared to hydrochloric acid. No explanation marks if observation is wrong. [1] [1] [1] Total:9 5 (a) Substance M is a good electrical conductor. Each carbon atom is covalently bonded to three other carbon atoms, thus having one valence electron not involved in bonding Presence of these d