RVHS Prelim P4 Soln

River Valley High School JC 2 H2 Chemistry 9729 2020 Prelim Practical Examination Suggested Solution RIVER VALLEY HIGH SCHOOL JC 2 PRELIM PRACTICAL EXAMINATION H2 CHEMISTRY 9729 PAPER 4 SUGGESTED SOLUTION 1 (a) Ksp = [Ca2+][IO3]2 (b) Results titration 1 2 final burette reading / cm3 19.60 39.20 initial burette reading/ cm3 0.00 19.60 volume of FA 2 used / cm3 19.60 19.60 (c) (i) average volume of FA 2 used = 19.60 19.60 2  =19.60 cm3 VFA 2 = 19.60 cm3 (ii) amount of S2O32 = 19.600.100 1000 = 0.00196 mol IO3  3I2  6S2O32 amount of IO3 in 25.0 cm3 of FA 1 = 0.00196  6 = 3.267  104 = 3.27  104 mol amount of IO3 in 25.0 cm3 of FA 1 = 3.27  104 mol (iii) amount of dissolved IO3 in the mixture from (b) at equilibrium = 4 100.03.267 10 25.0  = 1.307  103 mol amount of IO3(aq) in the mixture = 1.307  103 mol

River Valley High School JC 2 H2 Chemistry 9729 2020 Prelim Practical Examination Suggested Solution (d) (i) amount of IO3 from KIO3 = 100.00.0100 1000 = 0.00100 mol amount of IO3 from dissolved Ca(IO3)2 = 1.307  103  0.00100 = 3.07  104 mol amount of IO3(aq) from dissolved Ca(IO3)2 = 3.07  104 mol (ii) amount of Ca2+ in mixture = 43.07 10 2  = 1.535  104 = 1.54  104 mol (to 3 s.f.) amount of Ca2+(aq) in the mixture = 1.54  104 mol (e) [Ca2+]eqm = 41.535 10 0.100  = 1.535  103 mol dm3 [IO3]eqm = 31.307 10 0.100  = 1.307  102 mol dm3 Ksp = [Ca2+][IO3]2 = (1.535  103)( 1.307  102)2 = 2.62  107 mol3 dm9 (to 3 s.f.) Ksp = 2.62  107 mol3 dm9 (f) FA 1 would be diluted/ [IO3] in FA 1 is lowered/ lower amount of IO3 in 25.0 cm3 of FA 1. This forms less I2 for reaction with S2O32. Therefore, the mean titre would be lower. (g) The student did not carry out the experiment at 25 °C. Hence, the position of equilibrium for Ca(IO3)2(s)  Ca2+(aq) + 2IO3(aq) shifted to the left. OR When the student carried out the experiment, equilibrium has not been reached before filtering in (b) step 4. Hence, the [Ca2+] and [IO3] is lower.

River Valley High School JC 2 H2 Chemistry 9729 2020 Prelim Practical Examination Suggested Solution 2 (c) Results Shift 1 and timed practice Experiment VFA 5 / cm3 2HOV for solution A / cm3 VFA 6 / cm3 2HOV for solution B / cm3 t /s 1 t /s1 1 5.0 30.0 20.0 10.0 22.1 0.0425 2 10.0 25.0 20.0 10.0 11.1 0.0901 3 5.0 30.0 10.0 20.0 48.1 0.0208 Shift 2 Experiment VFA 5 / cm3 2HOV for solution A / cm3 VFA 6 / cm3 2HOV for solution B / cm3 t /s 1 t /s1 1 10.0 25.0 20.0 10.0 15.4 0.0649 2 20.0 15.0 20.0 10.0 8.0 0.125 3 10.0 25.0 10.0 20.0 28.3 0.0353 Shift 3 Experiment VFA 5 / cm3 2HOV for solution A / cm3 VFA 6 / cm3 2HOV for solution B / cm3 t /s 1 t /s1 1 10.0 25.0 20.0 7.0 11.8 0.0847 2