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?
- To find the concentration of a transition metal ion
- To find the volume of a transition metal ion
- To find the percentage error of a transition metal
- To find the number of moles of a transition metal
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Question 2 of 20

2. Question
How are redox titrations titrated?
- Oxidising agent titrated against a reducing agent
- Alkali titrated against an oxidising agent
- Reducing agent titrated against an oxidising agent
- 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.
- $MnO_4^- (aq) + 8H^+ (aq) + 5e^- – > Mn^{2+} (aq) + 4H_2O (l)$
- $MnO_4^- (aq) + 8H^+ (aq) + 5e^- - > Mn^+ (aq) + 4H_2O (l)$
- $MnO_4^- (aq) + H^+ (aq) + 5e^- - > Mn^+ (aq)$
- $MnO_4^- (aq) + H^+ (aq) + 5e^- - > Mn^+ (aq) + 4H_2O (l)$
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Question 4 of 20

4. Question
Write the equation for the reaction between Fe $^{2+}$ ions and MnO $_4$ $^-$ ions.
- $8H^+ (aq) + 5Fe^{2+} (aq) + MnO_4^- (aq) – > 5Fe^{3+} (aq) + Mn^{2+} (aq) + 4H_2O (l)$
- $8H^+ (aq) + 5Fe^{2+} (aq) + MnO_4^- (aq) – > 5Fe^{3+} (aq) + Mn^{2+} (l)$
- $H^+ (aq) + 5Fe^{2+} (aq) + MnO_4^- (aq) – > 5Fe^{3+} (aq) + Mn^{2+} (aq) + 4H_2O (l)$
- $H^+ (aq) + Fe^{2+} (aq) + MnO_4^- (aq) – > 5Fe^{3+} (aq) + Mn^{2+} (aq) + H_2O (l)$
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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?
- It is self-indicating
- Via a change in mas
- Via the production of gas
- 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 $_4$ $^-$ ?
- Purple to colourless/light pink
- Purple to blue
- Blue to purple
- Colourless/ light pink 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.
- $Cr_2O_7^{2-} (aq) + H^+ (aq) + 6e^- – > Cr_3^{3^}+ (aq) + H_2O (l)$
- $Cr_2O_7^{2-} (aq) + H^+ (aq) + 6e^- – > 2Cr_3^{3+} (aq) + H_2O (l)$
- $Cr_2O_7^{2-} (aq) + 14H^+ (aq) + 6e^- – > 2Cr_3^{3+} (aq)$
- $Cr_2O_7^{2-} (aq) + 14H^+ (aq) + 6e^- – > 2Cr_3^{3+} (aq) + 7H_2O (l)$
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Question 8 of 20

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

9. Question
Which indicator is used during the titration of potassium dichromate and Fe $^{2+}$ ?
- Diphenylamine sulfanate
- Phenolphthalein
- Methyl orange
- No indicator needed
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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?
- Violet/blue
- Red
- Purple
- Green/blue
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Question 11 of 20

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

12. Question
What oxidation state of iron, Fe $^{2+}$ or Fe $^{3+}$ , is more stable?
- Fe $^{3+}$
- Fe $^{2+}$
- Both have the same stability
- 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.
- $Cu^{2+} + e^- – > Cu^+$
- $Cu^{2+} + e^- – > Cu^{3+}$
- $Cu^{2+} + 2e^- – > Cu^{3+}$
- $Cu^{2+} + 2e^- – > Cu^+$
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Question 14 of 20

14. Question
What happens to Fe $^{2+}$ when added to air?
- Oxidises to form Fe $^{3+}$
- Reduces to form Fe $^{3+}$
- Oxidises to form Fe $^+$
- Reduces 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.
- $2Cu^{2+} (aq) + 4I^- (aq) – > 2CuI (s) + I_2 (aq)$
- $2Cu^{2+} (aq) + 4I^- (aq) – > 2CuI (s)$
- $Cu^{2+} (aq) + 4I^- (aq) – > 2CuI (s) + I_2 (aq)$
- $Cu^{2+} (aq) + 4I^- (aq) – > Cu^{2+} (s) + I_2 (aq)$
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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?
- Blue/black
- Yellow
- Brown
- Pale green
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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?
- White
- Brown
- Blue
- Green
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Question 18 of 20

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

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

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