Redox processes (First test)

For each question choose the answer you consider to be the best.

1. Which is correct statement about reduction?

A. It involves the loss of hydrogen.

B. It involves the addition of oxygen.

C. It involves the addition of electrons.

D. It involves an increase in oxidation number.

2. What is the correct name for FeSO₄?

A. iron(II) sulfite

B. iron(III) sulfite

C. iron(II) sulfate

D. iron(II) sulfide

3. What are the oxidation states of the elements in sulfuric acid, H₂SO₄?

4. What is the total of all the coefficients in the balanced half-equation below?

_ Cr₂O₇²⁻ + _ H⁺(aq) + _ e⁻ → _ Cr³⁺(aq) + _ H₂O(l)

A. 27

B. 28

C. 29

D. 30

5. Which change involves nitrogen being oxidized?

A. N₂H₄ → NH₂⁻

B. NO₂ → N₂O₄

C. NO₃⁻ → N₂O₅

D. N₂O → NO

6. Which changes are examples of reduction?

I. Cu²⁺ → Cu⁺

II. NH₃ → N₂

III. MnO₄⁻ → MnO₂

A. I and II only

B. I and III only

C. II and III only

D. I, II and III

7. Which reaction is not a redox reaction?

A. H₂S(g) + Cl₂(aq) → 2HCl(aq) + S(s)

B. Zn(s) + 2HCl(aq) → ZnCl₂(aq) + H₂(g)

C. Ag⁺(aq) + Cl⁻(aq) → AgCl(s)

D. 3H₂(g) + N₂(g) → 2NH₃(g)

8. In which reactions are carbon atoms oxidized?

I. C₂H₅OH → CH₃CHO + 2H⁺ + 2e⁻

II. C₂H₄ + Br₂ → C₂H₄Br₂

III. C₂H₅Br + OH⁻ → C₂H₅OH + Br⁻

A. I and II only

B. I and III only

C. II and III only

D. I, II and III

9. Two half-equations together with their standard electrode potentials are given :

Ni²⁺(aq) + 2e⁻ ⇌ Ni(s) E = – 0.26 V

Ag⁺(aq) + e⁻ ⇌ Ag(s) E= + 0.80 V

What is the cell potential in volts for the reaction below?

Ni(s) + 2Ag⁺(aq) → Ni²⁺(aq) + 2Ag(s)

A. + 1.06

B. + 0.54

C. – 1.06

D. + 1.86

10. Copper(I) ions can be oxidized and reduced at the same time in a process known as disproportionation.

2Cu⁺(aq) → Cu²⁺(aq) + Cu(s)

The two half-equations for this process are :

Cu²⁺(aq) + e⁻ ⇌ Cu⁺(aq) E= + 0.15 V

Cu⁺(aq) + e⁻ ⇌ Cu(s) E = + 0.52 V

What is the standard cell potential for the disproportionation reaction?

A. – 0.67 V

B. – 0.37 V

C. + 0.67 V

D. + 0.37 V

11. Which conditions are correct for the standard hydrogen electrode?

I. 1.00 mol dm^-3 of any acid solution

II. 25 ^oC (298 K)

III. H₂(g) at 1.00 x 10⁵ Pa (1 atmosphere) pressure

A. I and II only

B. I and III only

C. II and III only

D. I, II and III

12. A voltaic cell is constructed from a half-cell consisting of a piece of iron in a solution of iron(II) ions connected to a half-cell consisting of a piece of copper in a solution of copper(II) ions. Iron is more reactive than copper. Which statement is correct?

A. Iron atoms lose electrons.

B. Electrons flow from the copper half-cell to the iron half-cell.

C. The mass of the negative electrode increases.

D. The concentration of Cu²⁺(aq) ions increases.

13. What process occurs at the positive electrode in a voltaic cell and in an electrolytic cell?

14. Which are correct for a spontaneous reaction occurring in any voltaic cell?

I. E for the cell has a positive value

II. ∆G for the reaction has a negative value

III. The reaction must occur under standard conditions

A. I and II only

B. I and III only

C. II and III only

D. I, II and III

15. Electricity is passed through molten solutions of sodium chloride and calcium chloride connected in series. Which statement is correct?

A. The mass of calcium deposited will be more than the mass of sodium deposited.

B. The amount (in mol) of sodium deposited will be twice the amount (in mol) of calcium
deposited.

C. The amount (in mol) of sodium deposited will be half the amount (in mol) of calcium
deposited.

D. The mass of calcium deposited will be the same as the mass of sodium deposited.

16. Which factor will have the greatest effect on the amount (in mol) of oxygen produced during the electrolysis of dilute sulfuric acid?

A. Decreasing the temperature

B. Increasing the surface area of the inert positive electrode

C. Increasing the current

D. Decreasing the surface area of the inert negative electrode

17. Which are correct statements about cells?

I. Electrolytic cells contain a salt bridge

II. In a voltaic cell electrons are produced at the negative electrode

III. In an electrolytic cell cations accept electrons at the negative electrode

A. I and II only

B. I and III only

C. II and III only

D. I, II and III

18. A metal object is electroplated with silver using a solution of silver nitrate. One of the electrodes is the object to be plated and the other electrode is pure silver. Which statement is correct?

A. The object to be plated with silver is the negative electrode

B. The concentration of Ag⁺(aq) decreases during the process

C. The reaction occurring at the positive electrode is Ag⁺ + e^- → Ag(s)

D. The positive electrode increases in mass

19. During the electrolysis of dilute sodium hydroxide solution using inert electrodes, 20.0 cm³ of oxygen gas was evolved. What volume of gas would be evolved at the other electrode?

A. 5.0 cm³

B. 10.0 cm³

C. 20 cm³

D. 40 cm³

20. Which changes always increase the amount (in mol) of metal deposited during the electrolysis of a molten salt?

I. Passing the electricity for a longer period of time

II. Using a metal ion with a lower charge

III. Using a metal ion with a higher relative atomic mass

A. I and II only

B. I and III only

C. II and III only

D. I, II and III

Answers

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