Secondary 4 Combined Science Chemistry Redox Electrochemistry Quiz

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Secondary 4 Combined Science Chemistry Quiz - Redox Electrochemistry

Name: ____________________ Class: __________ Date: __________ Score: ________

Duration: 60 minutes
Total Marks: 45 marks

Instructions:

• Answer all questions.
• For calculation questions, show all working and provide answers to 3 significant figures.
• Use the relative atomic masses: H=1, O=16, Na=23, Mg=24, Al=27, Cu=64, Zn=65, Ag=108.

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

1. Which of the following is the correct definition of oxidation? (A) Gain of electrons (B) Loss of oxygen (C) Loss of electrons (D) Gain of hydrogen [1] Answer: ________

2. In the reaction $\text{Zn(s)} + \text{CuSO}_4\text{(aq)} \rightarrow \text{ZnSO}_4\text{(aq)} + \text{Cu(s)}$, which species is the reducing agent? [1] Answer: ________

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

4. Define "Redox reaction". [1] Answer: ___________________________________________________________________________

5. Which metal is more reactive than copper but less reactive than magnesium? (A) Gold (B) Zinc (C) Silver (D) Platinum [1] Answer: ________

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

7. Identify the process that occurs at the cathode during electrolysis. [1] Answer: ________

8. Which of the following is a strong oxidizing agent? (A) $\text{Na}_2\text{O}$ (B) $\text{KClO}_3$ (C) $\text{MgO}$ (D) $\text{LiF}$ [1] Answer: ________

9. What is the purpose of adding an electrolyte to a solvent in an electrochemical cell? [1] Answer: ___________________________________________________________________________

10. State the charge of the anode in an electrolytic cell. [1] Answer: ________

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Section B: Structured Response (11-15)

11. Consider the reaction: $\text{Fe}_2\text{O}_3\text{(s)} + 3\text{CO(g)} \rightarrow 2\text{Fe(s)} + 3\text{CO}_2\text{(g)}$ (a) Identify the substance being reduced. [1] (b) Explain your answer in (a) in terms of oxygen transfer. [1] Answer: ___________________________________________________________________________

12. A student sets up a simple cell using a zinc electrode and a copper electrode in a salt bridge system. (a) Which electrode acts as the anode? [1] (b) Describe the movement of electrons in the external circuit. [1] Answer: ___________________________________________________________________________

13. Electroplating a steel spoon with silver is carried out using a solution of $\text{AgNO}_3$. (a) Which electrode should the steel spoon be connected to? [1] (b) Why is a pure silver rod used as the other electrode? [1] Answer: ___________________________________________________________________________

14. The oxidation state of Sulfur in $\text{H}_2\text{SO}_4$ is +6. (a) Calculate the oxidation state of Sulfur in $\text{SO}_2$. [1] (b) State whether the change from $\text{H}_2\text{SO}_4$ to $\text{SO}_2$ is oxidation or reduction. [1] Answer: ___________________________________________________________________________

15. Explain why aluminum is extracted using electrolysis rather than by heating its oxide with carbon. [2] Answer: ___________________________________________________________________________

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Section C: Application & Analysis (16-20)

16. A piece of magnesium ribbon is placed in a solution of copper(II) nitrate. (a) State one observation. [1] (b) Write the balanced ionic equation for the reaction. [2] Answer: ___________________________________________________________________________

17. In the electrolysis of concentrated aqueous sodium chloride (brine): (a) Name the gas evolved at the anode. [1] (b) Explain why hydrogen gas is produced at the cathode instead of sodium metal. [2] Answer: ___________________________________________________________________________

18. Compare the reactivity of Metal A and Metal B. Metal A displaces Metal B from its salt solution. (a) Which metal is more reactive? [1] (b) If Metal B is Zinc, suggest a possible identity for Metal A. [1] Answer: ___________________________________________________________________________

19. Describe how the process of "sacrificial protection" prevents the rusting of iron pipes. [2] Answer: ___________________________________________________________________________

20. An electrolytic cell contains aqueous $\text{CuSO}_4$ with copper electrodes. (a) Describe the change in mass of the anode over time. [1] (b) Explain why the concentration of $\text{Cu}^{2+}$ ions in the electrolyte remains constant. [2] Answer: ___________________________________________________________________________

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Answer Key - Redox Electrochemistry Quiz

1. (C) Loss of electrons

2. $\text{Zn(s)}$ (It loses electrons/is oxidized)

3. +7 (K=+1, O=-2 $\times$ 4 = -8; Mn must be +7 to balance)

4. A chemical reaction in which both oxidation and reduction occur simultaneously.

5. (B) Zinc

6. Brown fumes of bromine gas are evolved.

7. Reduction (gain of electrons)

8. (B) $\text{KClO}_3$

9. To allow the flow of current/ions through the solution.

10. Positive (+)

11. (a) $\text{Fe}_2\text{O}_3$ (Iron(III) oxide) (b) It loses oxygen to become iron.

12. (a) Zinc electrode (b) Electrons flow from the zinc electrode (anode) to the copper electrode (cathode).

13. (a) Cathode (negative electrode) (b) To replenish the silver ions in the electrolyte as they are deposited on the spoon.

14. (a) +4 (b) Reduction

15. Aluminum is more reactive than carbon; therefore, carbon cannot reduce aluminum oxide. Electrolysis is required to break the strong bonds.

16. (a) Blue solution fades / Brown solid forms on the magnesium ribbon. (b) $\text{Mg(s)} + \text{Cu}^{2+}\text{(aq)} \rightarrow \text{Mg}^{2+}\text{(aq)} + \text{Cu(s)}$

17. (a) Chlorine gas (b) Hydrogen is lower in the reactivity series than sodium; $\text{H}^+$ ions are more easily reduced than $\text{Na}^+$ ions in aqueous solution.

18. (a) Metal A (b) Magnesium (or any metal above Zinc in the reactivity series, e.g., Iron is below, so Mg/Al)

19. A more reactive metal (e.g., Zinc) is attached to the iron. The more reactive metal oxidizes preferentially (sacrifices itself), preventing the iron from losing electrons.

20. (a) The mass of the anode decreases. (b) The rate at which copper is dissolved at the anode equals the rate at which copper is deposited at the cathode.