JANUARY 1995 CHEMISTRY 12 PROVINCIAL EXAMINATION ANSWER KEY / SCORING GUIDE

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1 JNRY 99 EMISTRY PROVINIL EXMINTION NSWER EY / SORING GIE TOPIS. inetics. Equilibrium. Solubility. cids, ases, Salts. Oxidation Reduction PRT : MLTIPLE-OIE Q T S GR Q T S GR I-- I-- I-- I--6 I-F- II-- II-G- II-E- II-I- II-- II-F- II-- II-J- III--8 III-- III-- III--7 III-- III-- III--6 IV-- IV-- IV-G- IV--, J E L E IV-- IV-F- IV-F-9 IV-G- IV--9 IV--9 IV-I- IV-J- IV-J-6 IV-- IV-L- IV-L- V--, - V-- V-- V--, G- V--, V-E- T E V-G-6 V-G- V-G-0, V-I- V-J- 9chpk - - pril, 996

2 PRT : WRITTEN-RESPONSE Q T S GR Q T S GR I-- I-- II-- II-J- III--, III--6 IV IV-F-, G- IV-F-7, -9 IV-- V--, V-E- V-J- Multiple-choice = 8 (8 questions) Written-response = ( questions) Total = 80 marks LEGEN: Q = Question = ognitive level T = Topic = eyed response S = Score GR = urriculum Guide Reference = Score box number 9chpk - - pril, 996

3 PRT : WRITTEN-RESPONSE. State two reasons why some collisions may not result in a chemical reaction. ( marks) Reason I: Reason II: For example: Reason I: unfavourable collision geometry/orientation mark Reason II: insufficient collision energy/low E mark 9chpk - - pril, 996

4 . escribe the relationship between activation energy and the rate of a chemical reaction. ( marks) For example: If the activation energy is lower, then the rate of reaction is greater. 9chpk - - pril, 996

5 . What is equal in a chemical reaction that has reached a state of equilibrium? ( marks) The rates of the forward and reverse reactions. 9chpk - - pril, 996

6 . onsider the following equilibrium: N ( g) + ( g) N ( g) eq = 66 at 00 t equilibrium, N equilibrium mixture. [ ] is.06 mol/ L and [ ] is 0.6 mol/ L. alculate [ N ] in the ( marks) eq = [ N ] [ N ] [ ] mark 66 = [ N ]. 06 ( )( 0. 6) mark [ N ]= 7.9 mark 9chpk pril, 996

7 ..0 M solution of sodium sulphite is added to a.0 M solution of copper(ii) chloride resulting in the formation of a precipitate. a) Identify the precipitate. ( mark) opper(ii) sulphite or uso b) Write the complete ionic equation for the reaction. ( mark) + Na ( aq) or + Na ( aq) +SO ( aq) +SO aq +u aq ( ) ( ) +u ( aq) + +l aq + +l aq ( ) uso ( s) +Na ( aq) ( ) uso ( s) +Na ( aq) + + +l ( aq) +l ( aq) c) Identify all spectator ions. ( mark) Na +, l 9chpk pril, 996

8 6. In an experiment, 00.0 ml samples containing silver ions are titrated with 0.00 M SN. The equation for the reaction is + g ( aq) The following data are recorded. +SN ( aq) gsn ( s) Trial Volume SN (ml) alculate the concentration of the silver ion in the solution. ( marks) [ g + ]= verage volume = =.60 ml mark mol SN 0.00 mol = L L mark = 0.00 mol mol g + = 0.00 mol 0.00 mol L mark = 0.0 M mark NOTE: educt point for incorrect significant figures. 9chpk pril, 996

9 7. a) Write the rönsted-lowry acid-base equation for the reaction between N ( aq) and N ( aq). ( mark) N ( aq) +N ( aq) N ( aq) + +N ( aq) b) Write a conjugate acid-base pair from the equation above. ( mark) N and N or N + and N 9chpk pril, 996

10 8. a) Write the formula of an amphiprotic anion that will act as an acid when added to water. ( mark) For example: PO or SO b) Write a hydrolysis equation to represent the anion selected in part (a) above behaving as an acid. ( mark) For example: PO + O O + + PO or SO + O O + + SO 9chpk pril, 996

11 9. alculate the p of a solution prepared by dissolving 0.00 mol of NaO in enough water to make 00.0 ml of solution. ( marks) For example: [ O ]= 0.00 mol / 0.00 L = 0.00 M mark w = [ O + ][ O ] mark ( 0.0M) O + [ ]=. 0 0 mark [ O + ]=. 0 0 M p =.00 mark NOTE: educt point for incorrect significant figures. 9chpk - - pril, 996

12 0. alculate the p of 0.0 M S. ( marks) For example: S + + S I x x x E 0.0 x x x marks ( x is small, therefore 0.0 x 0.0) mark [ ][ S ] a = + [ S] mark for expression = x 0.0 mark for substitution x =. 0 M = [ + ] mark for solving [ + ] p = log[ + ]=.67 mark for calculating p 9chpk - - pril, 996

13 . onsider the following equation: NO N O a) oes the above represent a redox reaction? ( mark) No. b) Explain. ( marks ) The oxidation number of nitrogen in NO and in N O is +. With no change in the oxidation number there is no loss or gain of electrons. 9chpk - - pril, 996

14 . alance the following half-reaction in acidic conditions. ( marks) r ro r + 6 O ro e marks One-half mark for each step: balancing bromine balancing oxygen balancing hydrogen balancing charge 9chpk - - pril, 996

15 . onsider the electrolysis of molten magnesium chloride. a) Identify the product formed at the anode. ( mark) hlorine gas or l b) Write the equation for the reduction half-reaction. ( mark) Mg + + e Mg c) Write the equation for the overall reaction. ( mark) Mgl () l Mg () l +l ( g) or Mg l () + +l l () Mg () l +l ( g) EN OF EY 9chpk - - pril, 996