Secondary 4 Pure Chemistry Redox Electrochemistry Quiz

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Secondary 4 Pure Chemistry Quiz - Redox Electrochemistry

Name: ____________________
Class: ____________________
Date: ____________________
Score: ________ / 50

Duration: 60 Minutes
Total Marks: 50
Instructions: Answer all questions. Show all working for calculations. Write balanced chemical equations with state symbols where required.

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Section A: Multiple Choice & Short Answer (Questions 1–10)

1. Define "oxidation" in terms of electron transfer. [1]

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2. In the reaction $\text{Mg(s)} + \text{Cu}^{2+}(\text{aq}) \rightarrow \text{Mg}^{2+}(\text{aq}) + \text{Cu(s)}$, identify the reducing agent. [1]

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3. State the oxidation state of Manganese (Mn) in $\text{KMnO}_4$. [1]

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4. A student adds acidified potassium manganate(VII) to a solution of $\text{Fe}^{2+}$ ions. State the color change observed. [1]

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5. Which of the following is a strong oxidizing agent? [1] (a) $\text{Zn}$
   (b) $\text{NaI}$
   (c) $\text{K}_2\text{Cr}_2\text{O}_7$
   (d) $\text{Mg}$

   Answer: ________

6. Write the ionic half-equation for the oxidation of $\text{Al}$ to $\text{Al}^{3+}$. [1]

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7. In the electrolysis of molten lead(II) bromide, what is the observation at the anode? [1]

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8. Define "selective discharge" in the context of aqueous electrolysis. [2]

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9. Why is graphite used as an electrode in many electrolysis cells? [1]

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10. State the product formed at the cathode during the electrolysis of concentrated aqueous sodium chloride. [1]

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Section B: Structured Response (Questions 11–20)

11. A simple cell is constructed using a Zinc electrode and a Copper electrode immersed in their respective sulfate solutions. (a) Identify the anode and the cathode. [2] Anode: ____________________ Cathode: ____________________ (b) In which direction do electrons flow through the external wire? [1]

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12. For the cell described in Question 11: (a) Write the half-equation for the reaction occurring at the anode. [2]

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    (b) Write the half-equation for the reaction occurring at the cathode. [2]

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13. Explain why a salt bridge is necessary in a galvanic cell. [2]

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14. During the electrolysis of aqueous copper(II) sulfate using copper electrodes: (a) Describe what happens to the mass of the anode. [1]

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    (b) Explain the observation in (a) using a half-equation. [2]

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15. Electroplating is used to coat a steel spoon with silver. (a) Which electrode should the steel spoon be made of (anode or cathode)? [1]

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    (b) Suggest a suitable electrolyte for this process. [1]

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16. A hydrogen fuel cell is used to power a vehicle. (a) State the fuel and the oxidant used in this cell. [2] Fuel: ____________________ Oxidant: ____________________ (b) Write the overall balanced equation for the reaction in the fuel cell. [2]

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17. Compare the electrolysis of molten $\text{NaCl}$ and aqueous $\text{NaCl}$. (a) State the product formed at the cathode for molten $\text{NaCl}$. [1]

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    (b) State the product formed at the cathode for aqueous $\text{NaCl}$. [1]

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18. Explain why $\text{Na}^+$ ions are not discharged at the cathode during the electrolysis of aqueous $\text{NaCl}$. [2]

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19. A metal $M$ is more reactive than Copper but less reactive than Zinc. (a) Predict whether $M$ will displace Copper from a solution of $\text{CuSO}_4$. [1]

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    (b) Predict whether $M$ will displace Zinc from a solution of $\text{ZnSO}_4$. [1]

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20. Describe the process of copper purification using electrolysis. Include the materials used for the anode and cathode. [3]

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Answer Key - Redox Electrochemistry Quiz

1. Oxidation is the loss of electrons. [1]
2. $\text{Mg(s)}$ (It is oxidized, therefore it is the reducing agent). [1]
3. +7 [1]
4. Purple to colorless. [1]
5. (c) $\text{K}_2\text{Cr}_2\text{O}_7$ [1]
6. $\text{Al(s)} \rightarrow \text{Al}^{3+}(\text{aq}) + 3\text{e}^-$ [1]
7. Brown fumes of bromine gas are evolved. [1]
8. The process where the ion that is more easily reduced (lower in the electrochemical series/more likely to gain electrons) is discharged at the cathode, and the ion more easily oxidized is discharged at the anode. [2]
9. It is chemically inert and conducts electricity. [1]
10. Hydrogen gas ($\text{H}_2$). [1]
11. (a) Anode: Zinc; Cathode: Copper [2] (b) From Zinc (anode) to Copper (cathode). [1]
12. (a) $\text{Zn(s)} \rightarrow \text{Zn}^{2+}(\text{aq}) + 2\text{e}^-$ [2] (b) $\text{Cu}^{2+}(\text{aq}) + 2\text{e}^- \rightarrow \text{Cu(s)}$ [2]
13. To maintain electrical neutrality by allowing ions to migrate between the two half-cells, completing the circuit. [2]
14. (a) The mass of the anode decreases. [1] (b) Copper atoms from the anode are oxidized to $\text{Cu}^{2+}$ ions: $\text{Cu(s)} \rightarrow \text{Cu}^{2+}(\text{aq}) + 2\text{e}^-$. [2]
15. (a) Cathode [1] (b) Silver nitrate ($\text{AgNO}_3$) or any soluble silver salt. [1]
16. (a) Fuel: Hydrogen ($\text{H}_2$); Oxidant: Oxygen ($\text{O}_2$) [2] (b) $2\text{H}_2(\text{g}) + \text{O}_2(\text{g}) \rightarrow 2\text{H}_2\text{O}(\text{l})$ [2]
17. (a) Sodium metal ($\text{Na}$) [1] (b) Hydrogen gas ($\text{H}_2$) [1]
18. Hydrogen is lower in the reactivity series (more easily reduced) than sodium; therefore, $\text{H}^+$ ions are selectively discharged instead of $\text{Na}^+$. [2]
19. (a) Yes [1] (b) No [1]
20. An impure copper block is used as the anode and a pure copper strip as the cathode. [1] Copper from the impure anode is oxidized to $\text{Cu}^{2+}$ ions, [1] which migrate to the cathode and are reduced to pure copper metal. [1]