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CHE 105/110 Introduction to Chemistry - Exercises and Answers

Oxidation-Reduction Reactions

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QUESTION ANSWER

1.

Is the reaction

2K(s) + Br2(ℓ) → 2KBr(s)
 

an oxidation-reduction reaction? Explain your answer.

1.

Yes; both K and Br are changing oxidation numbers.

3.

In the reaction

2Ca(s) + O2(g) → 2CaO
 

indicate what has lost electrons and what has gained electrons.

3.

Ca has lost electrons, and O has gained electrons.

5.

In the reaction

2Li(s) + O2(g) → Li2O2(s)

indicate what has been oxidized and what has been reduced.

5.

Li has been oxidized, and O has been reduced.

7.

What are two different definitions of oxidation?

7.

loss of electrons; increase in oxidation number.

9.

Assign oxidation numbers to each atom in each substance.

  1. P4
  2. SO2
  3. SO22−
  4. Ca(NO3)2

9.

  1. P: 0
  2. S: +4; O: −2
  3. S: +2; O: −2
  4. Ca: 2+; N: +5; O: −2

11.

Assign oxidation numbers to each atom in each substance.

  1. CO
  2. CO2
  3. NiCl2
  4. NiCl3

11.

  1. C: +2; O: −2
  2. C: +4; O: −2
  3. Ni: +2; Cl: −1
  4. Ni: +3; Cl: −1

13.

Assign oxidation numbers to each atom in each substance.

  1. CH2O
  2. NH3
  3. Rb2SO4
  4. Zn(C2H3O2)2

13.

  1. C: 0; H: +1; O: −2
  2. N: −3; H: +1
  3. Rb: +1; S: +6; O: −2
  4. Zn: +2; C: 0; H: +1; O: −2

15.

Identify what is being oxidized and reduced in this redox equation by assigning oxidation numbers to the atoms.

2NO + Cl2 → 2NOCl

15.

N is being oxidized, and Cl is being reduced.

17.

Identify what is being oxidized and reduced in this redox equation by assigning oxidation numbers to the atoms.

2KrF2 + 2H2O → 2Kr + 4HF + O2

17.

O is being oxidized, and Kr is being reduced.

19.

Identify what is being oxidized and reduced in this redox equation by assigning oxidation numbers to the atoms.

2K + MgCl2 → 2KCl + Mg
 19.

K is being oxidized, and Mg is being reduced.

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