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13.E: Oxidation and Reduction (Exercises)

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    Is the reaction

    2K(s) + Br2(ℓ) → 2KBr(s)

    an oxidation-reduction reaction? Explain your answer.

    1. Is the reaction NaCl(aq) + AgNO3(aq) → NaNO3(aq) + AgCl(s)

      an oxidation-reduction reaction? Explain your answer.

    2. In the reaction 2Ca(s) + O2(g) → 2CaO

      indicate what has lost electrons and what has gained electrons.

    3. In the reaction 16Fe(s) + 3S8(s) → 8Fe2S3(s)

      indicate what has lost electrons and what has gained electrons.

    4. In the reaction 2Li(s) + O2(g) → Li2O2(s)

      indicate what has been oxidized and what has been reduced.

    5. In the reaction 2Ni(s) + 3I2(s) → 2NiI3(s)

      indicate what has been oxidized and what has been reduced.

    6. What are two different definitions of oxidation?
    1. What are two different definitions of reduction?
    2. Assign oxidation numbers to each atom in each substance.
      1. P4
      2. SO2
      3. SO22−
      4. Ca(NO3)2
    3. Assign oxidation numbers to each atom in each substance.
      1. PF5
      2. (NH4)2S
      3. Hg
      4. Li2O2 (lithium peroxide)
    4. Assign oxidation numbers to each atom in each substance.
      1. CO
      2. CO2
      3. NiCl2
      4. NiCl3
    5. Assign oxidation numbers to each atom in each substance.
      1. NaH (sodium hydride)
      2. NO2
      3. NO2−
      4. AgNO3
    6. Assign oxidation numbers to each atom in each substance.
      1. CH2O
      2. NH3
      3. Rb2SO4
      4. Zn(C2H3O2)2
    7. Assign oxidation numbers to each atom in each substance.
      1. C6H6
      2. B(OH)3
      3. Li2S
      4. Au
    8. Identify what is being oxidized and reduced in this redox equation by assigning oxidation numbers to the atoms.

    2NO + Cl2 → 2NOCl

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

    Fe + SO3 → FeSO3

    1. Identify what is being oxidized and reduced in this redox equation by assigning oxidation numbers to the atoms. 2KrF2 + 2H2O → 2Kr + 4HF + O2
    2. Identify what is being oxidized and reduced in this redox equation by assigning oxidation numbers to the atoms. SO3 + SCl2 → SOCl2 + SO2
    3. Identify what is being oxidized and reduced in this redox equation by assigning oxidation numbers to the atoms. 2K + MgCl2 → 2KCl + Mg
    1. Identify what is being oxidized and reduced in this redox equation by assigning oxidation numbers to the atoms.

    C7H16 + 11O2 → 7CO2 + 8H2O

    Answers

    1. Yes; both K and Br are changing oxidation numbers.
    3. Ca has lost electrons, and O has gained electrons.
    5. Li has been oxidized, and O has been reduced.
    7. loss of electrons; increase in oxidation number
      1. P: 0
      2. S: +4; O: −2
      3. S: +2; O: −2
      4. Ca: 2+; N: +5; O: −2
      1. C: +2; O: −2
      2. C: +4; O: −2
      3. Ni: +2; Cl: −1
      4. Ni: +3; Cl: −1
      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. N is being oxidized, and Cl is being reduced.
    17. O is being oxidized, and Kr is being reduced.
    19. K is being oxidized, and Mg is being reduced.

    Additional Exercises

    1. What is the difference between a combination reaction and a redox reaction? Are all combination reactions also redox reactions? Are all redox reactions also combination reactions?

    2. Are combustion reactions always redox reactions as well? Explain.

    3. A friend argues that the equation

      Fe2+ + Na → Fe + Na+

      is balanced because each side has one iron atom and one sodium atom. Explain why your friend is incorrect.

    4. Historically, the first true battery was the Leclanché cell, named after its discoverer, Georges Leclanché. It was based on the following reaction:

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

      Identify what is being oxidized, what is being reduced, and the respective reducing and oxidizing agents.

    Answers

    1. A combination reaction makes a new substance from more than one reactant; a redox reaction rearranges electrons. Not all combination reactions are redox reactions, and not all redox reactions are combination reactions.

    3. Your friend is incorrect because the number of electrons transferring is not balanced.

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