2022 Peirce Chemistry Answers

Solutions for 2022 4E Prelim Science Chemistry MCQ 1. A 2. C 3. D 4. C 5. D 6. D 7. A 8. C 9. C 10. B 11. B 12. C 13. A 14. B 15. A 16. C 17. D 18. D 19. B 20. B Section A 1(a) Chromatography [1] 1(b) Any height below the starting line. [1] 1(c) Yes. It contains only permitted dyes. [1] 1(d) To check if athletes consumed banned drugs. or To check the vegetables contained too much pesticides [1] Total 4 Marks 2 A: dilute sulfuric acid / H2SO4 [1] B: barium sulfate/ BaSO4 [1] C: ammonium sulfate / (NH4)2SO4 [1] D: ammonia [1] Total 4 Marks 3(a) D [1] 3(b) F [1] 3(c) C [1] 3(d) B [1] 3(e) C [1] Total 5 Marks

4(a) Number of protons 12 Number of neutrons 25-12 = 13 Number of electrons 12 3 correct 2 mks, less than 3 correct 1mk [2] (bi) Ionic bonding [1] (bii) 1 mk for each ion [2] Total 6 Marks 5(ai) 1+14+3(16) = 63 [1] 5(aii) 126/63 = 2 mol/dm3 [1] 5(b) No. of moles of magnesium carbonate = ½ x 1 = 0.5 mol [1] Total 3 Marks 6(ai) CaCO3 (s) + H2SO4 (aq) → CaSO4 (s) + H2O (l) + CO2 (g) OR CaO (s) + H2SO4 (aq) → CaSO4 (s) + H2O (l) Equation 1 mk S.S 1 mk [2] 6(aii) Filter the mixture and Collect the residue. Rinse with distilled water and Dry between sheets of filter paper. 4 steps 3 mks; 3 steps 2 mks; 2 steps 1mk [3] 6(bi) Substance oxidised: Fe Reason: oxidation state of Fe increases from 0 in Fe to +2 in FeSO4 [1] [1] 6(bii) Substance reduced: H2SO4 Reason: oxidation state of S decreases from +6 in H2SO4 to +4 in SO2 [1] [1] Total 9 Marks

7(a) Bromine / Br2 [1] 7(b) 7 [1] 7(c) X2 [1] 7(d) Any value more than 216 pm [1] 7e(i) LiX [1] 7e(ii) CX4 [1] Total 6 Marks 8(a) X: naphtha Y: kerosene Z: lubricating oil All correct 2 mks; less than 3 correct 1 mk [2] 8(b) C6H14 → C4H10 + C2H4 [1] 8(ci) [1] 8(cii) it produces toxic fumes when burnt. [1] Total 4 Marks 9(a) Test: Bubble butane and butene to aqueous bromine Results: Reddish brown aqueous bromine decolourise by butene rapidly Aqueous bromine remains unchanged by butane Test: 1mk Results: 1mk [1] [1] 9(b) List of substances and conditions: yeast, glucose (solution), Less than 37°C Chemical Equation: C6H12O6→ 2 CH3CH2OH + 2 CO2 [1] [1] Total 4 Marks

Section B 10(ai) 10(b) 10a(i)1 mark for correctly plotted points; 1 mark for curve of best fit 10(b) 1 mark for expt 2 and 3 respectively. [2] and [2] (aii) 6 min [1] (aiii) As the temperature increases, more particles possess energy more than or equal to Ea. OR As temperature increases, particles gain K.E and move faster. This increase the frequency of effective collision and increase the speed of reaction. [1] [1] [1] (c) No. of moles of Zn = 62/65 = 0.9538 mol No. of moles of H2 = 0.9538 mol Volume of gas = 0.9538 x 24 = 22.89 = 22.9 dm3 (3 s.f) [1] [1] Total 10 Marks

11(ai) TiCl4 + 2 Mg→ 2 MgCl2 + Ti [1] 11(aii) magnesium [1] 11(b) Note: ratio of Ti atoms: V atoms: Al atoms is 8: 1:1 estimated In pure titanium, it is made of atoms of the same sizes. In titanium alloy, atoms of different sizes disrupt the order arrangement and prevent the layers from sliding. [1] [1] [1] 11(c) Silvery / low density Reject shiny as this phrase is not used to describe group I metals in syllabus [1] 11(di) Fe2O3 + 3 CO → 2 Fe + 3 CO2 [1] 11(dii) Recycling is the process of smelting, collecting and remaking metals in new blocks of iron. [1] 11(diii) It saves costs / it conserves limited resources. [1] 11(div) Painting/oiling/greasing/plastic coating and any other scientifically correct answers. [1] Total 10 Marks

12(ai) Village B [1] 12(aii) Pollutants 1: methane Pollutants 2: oxides of nitrogen OR sulfur dioxide [1] [1] 12(bi) [1] 12(bii) Amount of energy: particles possess highest/largest amount of energy Movement: particles move/travel fast and random Arrangement: particles are far apart and disorderly [1] [1] [1] 12(ci) Decreases pH of water bodies causing death of aquatic animals/ decrease pH of soil leading to unable to support farming / corrode metal/limestone structures. Accept any other scientifically correct answers. [1] 12(cii) General formula: CnH2n+1COOH Structural formula: Accept drawing that is not full structural formula [1] [1] Total 10 Marks