Redox titrations

Last updated: 11/03/2020

WJEC A-Level Chemistry Unit 3.2 – Redox reactions Redox titrations

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Question 1 of 20

1. Question
Why are redox reactions used?
- 1. To find the volume of a transition metal ion
- 2. To find the number of moles of a transition metal
- 3. To find the concentration of a transition metal ion
- 4. To find the percentage error of a transition metal
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Question 2 of 20

2. Question
How are redox titrations titrated?
- 1. Oxidising agent titrated against a reducing agent
- 2. Alkali titrated against an oxidising agent
- 3. Reducing agent titrated against an oxidising agent
- 4. Alkali titrated against a reducing agent
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Question 3 of 20

3. Question
Write the equation for the reduction of MnO $_4$ $^-$ ions.
- 1. $MnO_4^- (aq) + H^+ (aq) + 5e^- – > Mn^+ (aq)$
- 2. $MnO_4^- (aq) + 8H^+ (aq) + 5e^- – > Mn^{2+} (aq) + 4H_2O (l)$
- 3. $MnO_4^- (aq) + H^+ (aq) + 5e^- – > Mn^+ (aq) + 4H_2O (l)$
- 4. $MnO_4^- (aq) + 8H^+ (aq) + 5e^- – > Mn^+ (aq) + 4H_2O (l)$
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Question 4 of 20

4. Question
Write the equation for the reaction between Fe $^{2+}$ ions and MnO $_4$ $^-$ ions.
- 1. $H^+ (aq) + 5Fe^{2+} (aq) + MnO_4^- (aq) – > 5Fe^{3+} (aq) + Mn^{2+} (aq) + 4H_2O (l)$
- 2. $8H^+ (aq) + 5Fe^{2+} (aq) + MnO_4^- (aq) – > 5Fe^{3+} (aq) + Mn^{2+} (l)$
- 3. $8H^+ (aq) + 5Fe^{2+} (aq) + MnO_4^- (aq) – > 5Fe^{3+} (aq) + Mn^{2+} (aq) + 4H_2O (l)$
- 4. $H^+ (aq) + Fe^{2+} (aq) + MnO_4^- (aq) – > 5Fe^{3+} (aq) + Mn^{2+} (aq) + H_2O (l)$
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Question 5 of 20

5. Question
How is the end point found for the reaction of Fe $^{2+}$ ions with MnO $_4$ $^-$ ions?
- 1. Via a change in mas
- 2. Via the production of gas
- 3. It is self-indicating
- 4. Using an indicator
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Question 6 of 20

6. Question
What colour change occurs at the point of the reaction between Fe $^{2+}$ with MnO $_4$ $^-$ ?
- 1. Purple to blue
- 2. Purple to colourless/light pink
- 3. Colourless/ light pink to purple
- 4. Blue to purple
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Question 7 of 20

7. Question
Write the equation for the reduction of Cr $_2$ O $_7$ $^{2-}$ ions.
- 1. $Cr_2O_7^{2-} (aq) + H^+ (aq) + 6e^- – > Cr_3^{3^}+ (aq) + H_2O (l)$
- 2. $Cr_2O_7^{2-} (aq) + H^+ (aq) + 6e^- – > 2Cr_3^{3+} (aq) + H_2O (l)$
- 3. $Cr_2O_7^{2-} (aq) + 14H^+ (aq) + 6e^- – > 2Cr_3^{3+} (aq)$
- 4. $Cr_2O_7^{2-} (aq) + 14H^+ (aq) + 6e^- – > 2Cr_3^{3+} (aq) + 7H_2O (l)$
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Question 8 of 20

8. Question
Write the equation for the reaction between Fe $^{2+}$ with Cr $_2$ O $_7$ $^{2-}$ .
- 1. $H^+ (aq) + Fe^{3+} (aq) + Cr_2O_7^{2-}(aq) – > 6Fe^{3+} (aq) + Cr_3^{3+} (l) + H_2O (l)$
- 2. $H^+ (aq) + 6Fe^{3+} (aq) + Cr_2O_7^{2-}(aq) – > 6Fe^{3+} (aq) + 2Cr_3^{3+} (l) + 7H_2O (l)$
- 3. $14H^+ (aq) + 6Fe^{3+} (aq) + Cr_2O_7^{2-}(aq) – > 6Fe^{3+} (aq) + 2Cr_3^{3+} (l)$
- 4. $14H^+ (aq) + 6Fe^{3+} (aq) + Cr_2O_7^{2-}(aq) – > 6Fe^{3+} (aq) + 2Cr_3^{3+} (l) + 7H_2O (l)$
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Question 9 of 20

9. Question
Which indicator is used during the titration of potassium dichromate and Fe $^{2+}$ ?
- 1. No indicator needed
- 2. Diphenylamine sulfanate
- 3. Phenolphthalein
- 4. Methyl orange
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Question 10 of 20

10. Question
What colour is the end point within the titration of potassium dichromate and Fe $^{2+}$ ions?
- 1. Red
- 2. Green/blue
- 3. Violet/blue
- 4. Purple
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Question 11 of 20

11. Question
Write the equation for the oxidation of I $^-$ ions.
- 1. $2I^- – > I^+ + 2e^-$
- 2. $2I^- – > I_2 + 2e^-$
- 3. $I^- – > I^+ + e^-$
- 4. $I^- – > I_2 + e^-$
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Question 12 of 20

12. Question
What oxidation state of iron, Fe $^{2+}$ or Fe $^{3+}$ , is more stable?
- 1. Fe $^{3+}$
- 2. Fe $^{2+}$
- 3. Both have the same stability
- 4. Depends which state they are in
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Question 13 of 20

13. Question
Write the equation for the reduction of Cu $^{2+}$ ions.
- 1. $Cu^{2+} + 2e^- – > Cu^{3+}$
- 2. $Cu^{2+} + e^- – > Cu^+$
- 3. $Cu^{2+} + e^- – > Cu^{3+}$
- 4. $Cu^{2+} + 2e^- – > Cu^+$
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Question 14 of 20

14. Question
What happens to Fe $^{2+}$ when added to air?
- 1. Reduces to form Fe $^+$
- 2. Oxidises to form Fe $^{3+}$
- 3. Reduces to form Fe $^{3+}$
- 4. Oxidises to form Fe $^+$
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Question 15 of 20

15. Question
Write the equation for the reaction between I $^-$ ions and Cu $^{2+}$ ions.
- 1. $2Cu^{2+} (aq) + 4I^- (aq) – > 2CuI (s) + I_2 (aq)$
- 2. $2Cu^{2+} (aq) + 4I^- (aq) – > 2CuI (s)$
- 3. $Cu^{2+} (aq) + 4I^- (aq) – > Cu^{2+} (s) + I_2 (aq)$
- 4. $Cu^{2+} (aq) + 4I^- (aq) – > 2CuI (s) + I_2 (aq)$
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Question 16 of 20

16. Question
What colour is the end point within the titration of I $^-$ ions and Cu $^{2+}$ ions?
- 1. Pale green
- 2. Brown
- 3. Yellow
- 4. Blue/black
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Question 17 of 20

17. Question
What colour precipitate is formed within the reaction between I $^-$ ions and Cu $^{2+}$ ions?
- 1. White
- 2. Brown
- 3. Blue
- 4. Green
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Question 18 of 20

18. Question
Which of the following is an oxidising agent?
- 1. Air
- 2. Methane
- 3. Hydrochloric acid
- 4. Carbon dioxide
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Question 19 of 20

19. Question
Write the equation for the oxidation of Fe $^{2+}$ .
- 1. $Fe^{2+}(aq) – > Fe^+(aq)$
- 2. $Fe^{2+}(aq) – > Fe^{3+}(aq) + e^-$
- 3. $Fe^{2+}(aq) – > Fe^+(aq) + e^-$
- 4. $Fe^{2+}(aq) – > Fe^{3+}(aq)$
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Question 20 of 20

20. Question
What type of ion is MnO $_4$ $^-$ ?
- 1. Reducing agent
- 2. Charged ion
- 3. Zwitterion
- 4. Oxidising agent
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