KEY AND SCORING GUIDE

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1 EY N SORING GIE HEMISTRY PROVINIL EXMINTION JNRY 99 June, 996 : PM

2 HEMISTRY PROVINIL EXMINTION EY N SORING GIE JNRY 99 TOPIS: ITEM LSSIFITION. inetics. Equilibrium. Solubility. cids, ases, Salts. Oxidation Reduction PRT : MLTIPLE HOIE QESTIONS Q T S GR Q T S GR H H I-- I-- I-- I--7 I-- II-- II-- II-- II-E- II-G-, II-H-, II-J- II-J- III-- III-- III-- III-- III-- III-- III-- IV--9 IV-- IV-- IV-- PRT : WRITTEN RESPONSE QESTIONS Q T S GR H H H H I-- I-- II-E- II-J- III-- III-- IV-- IV--6 IV-H- V-E- V-I-, IV-E- IV-F- IV-F-8 IV-F-9,H- IV-G- IV-L- IV-L- IV-I- IV-J- IV-J- IV--,G- IV-H-9 V-- V-- V--6 V-- V-- V-- V-F- V-G-7 V-G-9 V-H- V-I- V-I- NOTE: Q = Question number; = ox number; = ognitive level; T = Topic; = eyed Response; S = Score; GR = urriculum Guide Reference June, h/pey/january/9

3 HEMISTRY PROVINIL EXMINTION EY N SORING GIE JNRY 99 PRT : WRITTEN-RESPONSE QESTIONS ( marks total) QESTION:. onsider the following reaction: u + gno u( NO ) + g ( s) ( aq) ( aq) ( s) In a rate experiment, a coil of copper wire is placed into a solution of silver nitrate. The following data are recorded. Time (hours) Mass of opper (g) alculate the rate of this reaction. ( marks) for a correct numerical answer. for correct units. mark e.g. 0. grams/hour marks June, h/pey/january/9

4 HEMISTRY PROVINIL EXMINTION EY N SORING GIE JNRY 99 QESTION:. efine activated complex. ( marks) short-lived or unstable or high PE mark chemical species mark June, h/pey/january/9

5 HEMISTRY PROVINIL EXMINTION EY N SORING GIE JNRY 99 QESTION:. onsider the following equilibrium system: + ( aq ) ( aq ) + ( aq ) yellow colourless red Fe + SN FeSN In an experiment, a student places the above equilibrium system into a cold water bath and notes that the intensity of the red colour increases. The student then concludes that the equilibrium is exothermic. a) o you agree or disagree? ( ) b) Explain: marks ( mark ) agree with student mark cold water bath caused shift in forward direction mark when temp. is decreased, equil shifts in exo direction mark June, h/pey/january/9

6 HEMISTRY PROVINIL EXMINTION EY N SORING GIE JNRY 99 QESTION:. onsider the following equilibrium system: Pl + l Pl ( g) ( g) ( g) t 0, 0.0 mol of Pl and 0.60 mol of l are placed into a.0 litre container. t equilibrium, the Pl [ ] = 0. mol/l. alculate the value of eq. ( marks) Pl + l Pl ( g) ( g) ( g) I E marks for IE Pl / Pl l eq = [ ] [ ][ ] =( 0. )/( 09. )( 09. ) = 077. mark mark for substitution mark for final answer June, h/pey/january/9

7 HEMISTRY PROVINIL EXMINTION EY N SORING GIE JNRY 99 QESTION: ml solution containing 0. M l, 0. M NH and 0. M Mg + is added to a 00 ml solution containing 0. M S, 0. M l and 0. M OH. ( marks) Identify the ions that do not form a precipitate. + NH and l marks June, h/pey/january/9

8 HEMISTRY PROVINIL EXMINTION EY N SORING GIE JNRY 99 QESTION: 6. science teacher needs.0 L of limewater for an experiment. Limewater is a saturated solution of a(oh). alculate the minimum mass of a(oh) required to make this solution. sp =. 0 6 ( marks) 6 sp for a(oh) =. 0 + Let s = solubility of a(oh) =[ a ] s OH =[ ] + sp =[ a ] [ OH ] =( s)( s) = s 6 s =. 0 s = M marks a( OH) = 7. g/mol mark ( )( )( ) # g = mol /L 7. g/mol.0l =.g mark mark June, h/pey/january/9

9 HEMISTRY PROVINIL EXMINTION EY N SORING GIE JNRY 99 QESTION: 7. Write the equation for the hydrogen carbonate ion acting as a weak acid. ( mark) Example: + HO + H O H O + O mark June, h/pey/january/9

10 HEMISTRY PROVINIL EXMINTION EY N SORING GIE JNRY 99 QESTION: 8. a) student prepares a buffer by dissolving solid sodium acetate, NaH OO, in a solution of acetic acid, H OOH. Write the net ionic equation for the buffer system. ( mark) b) What happens to the concentrations of H OOH and H OO when a small amount of acid is added to this system? ( mark) Explain the reason. ( mark) c) What happens to the ph of the buffer when a small amount of acid is added? ( mark) a) H OOH + H O H OO + H O + mark OR H OO + H O H OOH + OH mark b) The H OOH will increase while the H OO will decrease. mark The added H O + reacts with H OO to produce H OOH. mark c) The ph remains relatively constant. mark June, h/pey/january/9

11 HEMISTRY PROVINIL EXMINTION EY N SORING GIE JNRY 99 QESTION: 9. etermine the ph of a 0.0 M solution of hydrogen cyanide. ( marks) HN H + N I E x + x + x 00. x 0 x [ + ] [ ] a = H N HN [ ] 0 = ( x )( x ) ( 00. ) ( 8. 0 )( 00. ) = ( x) marks + 6 [ H ]= mark 6 ph = log ( )= 6. x marks mark June, h/pey/january/9

12 HEMISTRY PROVINIL EXMINTION EY N SORING GIE JNRY 99 QESTION: 0. alance the following redox equation in an acidic solution. ( marks) + FeO + NH N + Fe For each balanced half-reaction H + FeO + e Fe + H O mark NH N + 6H + 6e mark + For multiplying top equation by mark For adding and cancelling electrons and H + mark OR + + FeO + 0H + NH Fe + 8H O + N } 678 (dec. of ) mk mk H + FeO + NH N + Fe H O mark Inc. of 6 mk June, h/pey/january/9

13 HEMISTRY PROVINIL EXMINTION EY N SORING GIE JNRY 99 QESTION:. In an electrolytic cell, current is passed through molten Nal. a) Suggest suitable electrodes for this process. ( mark) b) Write the equation for the reaction occurring at the cathode. ( mark) c) Write the overall equation. ( mark) a) Pt or carbon or other inert electrodes. mark + b) Na + e Na mark c) Nal Na + l mark EN OF EY June, h/pey/january/9