APRIL 1995 CHEMISTRY 12 PROVINCIAL EXAMINATION ANSWER KEY / SCORING GUIDE

Transcription

1 PRIL 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-- I-- II-- II-- II-- II-E- II-I- II-F- II-- II-G-, J- III--8 III-- III-- III--6 III-- III-- III-E- IV--, V-- IV-- IV--8 IV IV-- IV-F- IV-G- IV-- IV--9 IV-- IV-J- IV-I-, IV-- IV-L- IV-J- IV-L- V--, 6 V-- V-- V-- V-- V-E- V-G- V-G- V-G-7 V-- V-J- V-J- 9chpk - - pril, 996

2 PRT : WRITTEN-RESPONSE Q T S GR Q T S GR I-E- II--, II-- II-J- III-E- III--7 IV IV--, F-8, IV--9 IV-J- V--, V-F- 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. Nitric oxide (NO) is involved in the decomposition of ozone ( O ) by the following mechanism: Step O + sunlight O + O Step Step O + NO NO + O NO + O NO+O a) Write the net equation for the decomposition reaction. ( mark) Sunlight + O ( g) O ( g) b) Identify a catalyst. ( mark) NO is the catalyst. c) Identify a reaction intermediate. ( mark) NO or O are reaction intermediates. d) What is the function of sunlight in this reaction? ( mark) For example: To supply activation energy. 9chpk - - pril, 996

4 . a) Why are chemical equilibria referred to as dynamic? ( mark) oth the forward and reversed reactions continue to occur. b) ow is a chemical system at equilibrium recognized? ( mark) chemical system at equilibrium is recognized by its constant macroscopic properties. 9chpk - - pril, 996

5 . onsider the following equilibrium system: ( s) + ( g) ( g) eq = at student places. mol of carbon,.6 0 mol of hydrogen and. mol of methane in a.0 L flask. The student predicts that the [ ] increases as equilibrium is established. o you agree? Explain your answer using appropriate calculations. ( marks) Trial eq = [ ] [ ] mark =..6 0 ( ) mark =.9 0 [ ] Since Trial eq is less than the ctual eq, the forward reaction is favoured and the increases. mark Yes, I agree with the student. mark 9chpk - - pril, 996

6 . onsider the following solubility equilibrium: gio ( s) +heat g ( aq) + +IO ( aq) State two methods by which more gio solid may be precipitated out of solution. ( marks) For example: ecrease temperature. mark dd a soluble compound with a common ion. gno NaIO mark for either one. alculate the maximum moles of r that can exist in 0.00 L of 0.0 M Pb( NO ). ( marks) Since Pb( NO ) Pb + + NO [ Pb + ]= 0.0 M mark Pbr ( s) Pb ( aq) + +r aq ( ) mark sp = [ Pb + ][ r ] mark = ( 0.0 M) [ r ] mark [ r ]= 8. 0 M mark mol r = 8. 0 M 0.00 L =. 0 mol mark ( mark for incorrect sig. figs.) 9chpk pril, 996

7 6. In an acid-base reaction, the two rönsted-lowry acids are hydrofluoric acid (F) and the hydrogen sulphite ion SO ( ). Write the equation for this reaction. ( marks) F + SO SO + F 7. a) Write an equilibrium equation to represent the hydrolysis of ammonia in water. ( mark) N + O N + + O b) alculate the value of the equilibrium constant. ( mark) b = = chpk pril, 996

8 8. Tomato juice has a p of.0. alculate the [ O + ] and [ O ] in tomato juice. ( marks).0 = log[ O + ] 6. 0 M = [ O + ] mark. 0 0 = [ O + ][ O ], [ O ]= M mark ( mark for incorrect sig. figs.) 9. alculate the p of a solution prepared by adding 60.0 ml of 0.0 M l to 0.0 ml of 0.00 M O. ( marks) mol l = ( L) ( 0.0 M) = mol mark mol O ( 0.00 L) ( 0.00 M) = 0.00 mol mark mol excess O = mol mark [ O]= mol / L = 0.0 M mark po = log[ O ]=. 60 mark p =.00 po =. 0 mark 9chpk pril, 996

9 0. alance the following redox reaction. ( marks) u + NO u + + NO (in acid) ( ) mark for each half-reaction ( ) mark for balancing electrons u u + + e NO + + +e NO + O u + NO +8 + u + + NO+ O mark 9chpk pril, 996

10 . In a titration, a.00 ml sample of an antiseptic solution containing hydrogen peroxide required 7.6 ml of a M solution of MnO to reach the endpoint. The equation for the reaction is O + MnO O + Mn + +8 O a) Identify the reducing agent. ( mark) O b) alculate the concentration of O in the antiseptic solution. ( marks) mol MnO = M L = mol mark mol O = mol MnO mol O / mol MnO = mol mark mol [ O ]= = M mark L EN OF EY 9chpk pril, 996