Copy of AMKSS 2024 Chem P3 Answers

1 ANG MO KIO SECONDARY SCHOOL PRELIM EXAMINATION 2024 SECONDARY FOUR EXPRESS CHEMISTRY [6092/03] ANSWER SCHEME Paper 3: Chemistry Practical [40 Marks] Note: Overall deduct 1 mark if no 3 sf. Note: Overall deduct 1 mark if no unit. 1(a) Results Titration Number 1 2 3 Final burette reading / cm3 23.60 [shift 1] 23.80 [shift 2] 23.60 [shift 1] 23.80 [shift 2] Initial burette reading / cm3 0.00 0.00 Volume of potassium manganate(VII) used / cm3 23.60 [shift 1] 23.80 [shift 2] 23.60 [shift 1] 23.80 [shift 2] Best titration results (√) √ √ • Correct headings with units of measurement [1] • All burette readings for all accurate titres in titration table are recorded to nearest 0.05 cm3 [1] • Accuracy of titration results [2] - for the average titre within 0.20 cm3 of Supervisor’s average value score 2 marks - for the average titre within 0.30 cm3 of Supervisor’s average value score 1 mark • At least two titre values are within 0.20 cm3 [1] 5 1(b) Average volume of G = (23.60 + 23.60) / 2 = 23.60 cm3 1 1(c) Number of moles of H = 0.08 mol/dm3 x (25 / 1000) = 0.00200 mol ( 3sf ) 1 1(d) manganate(VII) ions : iron(II) ions MnO4- : Fe2+ 1 : 5 Moles of manganate(VII) ions = 0.002 ÷ 5 = 0.0004 [1] number of moles of manganate(VII) ions in 1 dm3 = 0.0004 ÷ (23.60/1000) = 0.0169491 = 0.0169 mol [1] Note: E.C.F allowed if working is correct. ( if 1c is wrong ) 2 1(e) Number of moles of manganate(VII) ions in 250 cm3 of G = 0.0169 ÷ 4 = 0.004225 mol = 0.00423 mol 1

2 Note: E.C.F allowed if working is correct. ( if 1d is wrong ) 1(f) Mr of Manganese = 55 Mass of manganese in 2.12g = 55 x 0.00423 = 0.23265 g = 0.233 g Note: E.C.F allowed if working is correct. ( if 1e is wrong ) 1 1(g) percentage by mass of manganese in mangalloy = (0.233 / 2.12) x 100% = 10.99% = 11.0% [1] Note: E.C.F allowed if working is correct. ( if 1f is wrong ) 1 1(h) Percentage mass will be higher. [1] The number of moles of G will be higher as concentration is divided by a lower volume. 1 2(a) total volume of Q added /cm3 highest temperature reached/°C [shift 1] highest temperature reached/°C [shift 2] 0.00 31.5 31.5 5.00 33.5 33.5 10.00 35.0 35.5 15.00 36.0 36.5 20.00 37.0 37.5 25.00 36.5 37.0 30.00 36.0 36.5 35.00 35.0 36.0 40.00 34.5 35.5 • All temperature readings are recorded to nearest 0.5 °C [1] • All data completed with correct trend [1] Note: As vol. of Q increases, temperature increases, As Q = 20.00 cm3, temperature is the highest. As vol. of Q continues to increases, temperature decreases. Minus 1 mark if there are 3 or more constant temperatures for the upward/downward trends respectively. 2 2(b) Plotting of graph • Labelled axes with units of measurement and appropriate scale for axes [1] • All points plotted accurately [1] • 2 Best-fit s