Ncea
90696
906960
For Supervisor’s use only
3
Level 3 Chemistry, 2008
90696 Describe oxidation-reduction processes
Credits: Three 9.30 am Friday 28 November 2008 Check that the National Student Number (NSN) on your admission slip is the same as the number at the top of this page. You should answer ALL the questions in this booklet. A periodic table is provided on the Resource Sheet L3–CHEMR. If you need more space for any answer, use the page(s) provided at the back of this booklet and clearly number the question. Check that this booklet has pages 2–8 in the correct order and that none of these pages is blank. YOU MUST HAND THIS BOOKLET TO THE SUPERVISOR AT THE END OF THE EXAMINATION.
For Assessor’s use only
Achievement Criteria Achievement with Merit
Explain and apply oxidationreduction processes.
Achievement
Describe oxidation-reduction processes.
Achievement with Excellence
Discuss oxidation-reduction processes.
Overall Level of Performance
© New Zealand Qualifications Authority, 2008 All rights reserved. No part of this publication may be reproduced by any means without the prior permission of the New Zealand Qualifications Authority.
2
You are advised to spend 35 minutes answering the questions in this booklet. QUESTION ONE (a) Sodium thiosulfate solution reacts with dilute acid to form a precipitate of sulfur, and sulfur dioxide. S2O32– + 2H+ → S + SO2 + H2O (i) Give the oxidation numbers for sulfur in the species below. S2O32– (ii) S SO2 .
Assessor’s use only
Write balanced half-equations for the oxidation and reduction reactions. Oxidation Reduction
(b)
Oxalic acid (H2C2O4) reacts with acidified potassium permanganate solution (MnO4– / H+). (i) Describe what would be observed.
(ii)
Write balanced half-equations for the oxidation and reduction reactions, and then write a balanced equation for the overall reaction. half-equation
half-equation
balanced equation for overall reaction
Chemistry 90696,
906960
For Supervisor’s use only
3
Level 3 Chemistry, 2008
90696 Describe oxidation-reduction processes
Credits: Three 9.30 am Friday 28 November 2008 Check that the National Student Number (NSN) on your admission slip is the same as the number at the top of this page. You should answer ALL the questions in this booklet. A periodic table is provided on the Resource Sheet L3–CHEMR. If you need more space for any answer, use the page(s) provided at the back of this booklet and clearly number the question. Check that this booklet has pages 2–8 in the correct order and that none of these pages is blank. YOU MUST HAND THIS BOOKLET TO THE SUPERVISOR AT THE END OF THE EXAMINATION.
For Assessor’s use only
Achievement Criteria Achievement with Merit
Explain and apply oxidationreduction processes.
Achievement
Describe oxidation-reduction processes.
Achievement with Excellence
Discuss oxidation-reduction processes.
Overall Level of Performance
© New Zealand Qualifications Authority, 2008 All rights reserved. No part of this publication may be reproduced by any means without the prior permission of the New Zealand Qualifications Authority.
2
You are advised to spend 35 minutes answering the questions in this booklet. QUESTION ONE (a) Sodium thiosulfate solution reacts with dilute acid to form a precipitate of sulfur, and sulfur dioxide. S2O32– + 2H+ → S + SO2 + H2O (i) Give the oxidation numbers for sulfur in the species below. S2O32– (ii) S SO2 .
Assessor’s use only
Write balanced half-equations for the oxidation and reduction reactions. Oxidation Reduction
(b)
Oxalic acid (H2C2O4) reacts with acidified potassium permanganate solution (MnO4– / H+). (i) Describe what would be observed.
(ii)
Write balanced half-equations for the oxidation and reduction reactions, and then write a balanced equation for the overall reaction. half-equation
half-equation
balanced equation for overall reaction
Chemistry 90696,