FORM 4 CHEM- ELECTROCHEMISTRY

1. Which statement is correct?

A. Oxidation involves loss of electrons and a decrease in oxidation state.

B. Oxidation involves gain of electrons and an increase in oxidation state.

C. Reduction involves loss of electrons and an increase in oxidation state.

D. Reduction involves gain of electrons and a decrease in oxidation state.

2. Ag(s) + NO₃^– (aq) + H+(aq) —– Ag+(aq) + NO(g) + H2O(l)

When the oxidation-reduction equation above is balanced, what is the coefficient for H+ (aq)?

A. 1

B. 2

C. 3

D. 4

3. Aqueous solutions of AgNO₃, Cu(NO₃)₂ and Cr(NO₃)₃ are electrolyzed using the same quantity of electricity. How do the number of moles of metal formed compare?

A. Ag = Cu = Cr

B. Ag > Cu > Cr

C. Ag < Cu < Cr

D. Cu > Ag > Cr

4. In which reaction does chromium undergo a change in oxidation number?

A. Cr2O3 + 3H2SO4 → Cr2(SO4)3 + 3H2O

B. Cr2(SO4) + 6NaOH → 2Cr(OH)3 + 3Na2SO4

C. K2Cr2O7 + 4H2SO4 + 6HCl → Cr2(SO4) + K2SO4 + 7H2O + 3Cl2

D. 2K2CrO4 + H2SO4 → K2Cr2O7 + K2SO4 + H2O

5. Which reaction does not involve either oxidation or reduction?

A. CH4(g) + 2O2(g) → CO2(g) + 2H2O(g)

B. Cu2+(aq) + Zn(s) → Cu(s) + Zn2+(aq)

C. CuO(s) + H2SO4(aq) → CuSO4(aq) + H2O(l)

D. Zn(s) + H2SO4(aq) → ZnSO4(aq) + H2(g)

6. For a voltaic (or galvanic) cell using Ag,Ag⁺ (1.0 M) and Zn,Zn²⁺ (1.0 M) half-cells, which of the following statements is incorrect?

A. The zinc electrode is the anode.

B. Electrons will flow through the external circuit from the zinc electrode to the silver electrode.

C. Reduction occurs at the zinc electrode as the cell operates.

D. The mass of the zinc electrode will decrease as the cell operates.

7. What happens to the Cr³⁺(aq) ion when it is converted to CrO₄^2- (aq)?

A. Its oxidation number decreases and it undergoes reduction.

B. Its oxidation number decreases and it undergoes oxidation.

C. Its oxidation number increases and it undergoes reduction.

D. Its oxidation number increases and it undergoes oxidation.

8. Consider the following reactions.

Cu2+(aq) + 2e− …….. Cu(s) Eï = +0.34 V

Mg2+(aq) + 2e− ……… Mg(s) Eï = −2.36 V

Zn2+(aq) + 2e− ……….. Zn(s) Eï = −0.76 V

Which statement is correct?

A. Cu2+(aq) will oxidize both Mg(s) and Zn(s).

B. Zn(s) will reduce both Cu(aq) and Mg2+(aq).

C. Mg2+(aq) will oxidize both Cu(s) and Zn(s).

D. Cu(s) will reduce both Mg2+(aq) and Zn2+(aq).

9. Consider the standard electrode potentials of the following reactions.

Cr³⁺(aq) + 3e →Cr(s) −0.75 V

Cd²⁺(aq) + 2e → Cd(s) −0.40 V

What is the value of the cell potential (in V) for the following reaction?

2Cr(s) + 3Cd²⁺(aq) → 2Cr³⁺(aq) + 3Cd(s)

A. −0.35

B. −1.15

C. +0.30

D. +0.35

10. What mass (in grams) of nickel could be electroplated from a solution of nickel(II) chloride by a current of 0.25 amperes flowing for 10 hours?

A. 12 g

B. 5.5 g

C. 0.046 g

D. 2.7 g

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