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Chapter 4: Problem 87

Balance each of the following oxidation-reduction reactions by using the oxidation states method. a. \(\mathrm{C}_{2} \mathrm{H}_{6}(\mathrm{~g})+\mathrm{O}_{2}(\mathrm{~g}) \rightarrow \mathrm{CO}_{2}(\mathrm{~g})+\mathrm{H}_{2} \mathrm{O}(g)\) b. \(\mathrm{Mg}(s)+\mathrm{HCl}(a q) \rightarrow \mathrm{Mg}^{2+}(a q)+\mathrm{Cl}^{-}(a q)+\mathrm{H}_{2}(g)\) c. \(\mathrm{Co}^{3+}(a q)+\mathrm{Ni}(s) \rightarrow \mathrm{Co}^{2+}(a q)+\mathrm{Ni}^{2+}(a q)\) d. \(\mathrm{Zn}(s)+\mathrm{H}_{2} \mathrm{SO}_{4}(a q) \rightarrow \mathrm{ZnSO}_{4}(a q)+\mathrm{H}_{2}(g)\)

Short Answer

Expert verified
The balanced equations for each reaction are as follows: a. C2H6 + 7/2 O2 --> 2CO2 + 3H2O b. Mg + 2H+ + 2Cl- --> Mg^2+ + 2Cl- + H2 c. 2Co^3+ + Ni --> 2Co^2+ + Ni^2+ d. Zn + 2H+ + SO4^2- --> Zn^2+ + SO4^2- + H2

Step by step solution

01

Oxidation half-reaction: C2H6 --> 2CO2 (Carbon in ethane is oxidized) Reduction half-reaction: O2 --> H2O (Oxygen is reduced) Step 2: Balance Atoms in Half-reactions

(We need to balance the C, H, and O atoms in the half-reactions) Oxidation: C2H6 --> 2CO2 Reduction: O2 --> 2H2O Step 3: Balance Charge Using H2O, H+, and e-
02

Since the charges in both half-reactions are already balanced, we can proceed to Step 4. Step 4: Select coefficients to balance the number of electrons

No change as the charges are balanced for both half-reactions. Step 5: Add the two balanced half-reactions
03

The balanced equation for reaction a: C2H6 + 7/2 O2 --> 2CO2 + 3H2O Reaction b. $\mathrm{Mg}(s)+\mathrm{HCl}(a q) \rightarrow \mathrm{Mg}^{2+}(a q)+\mathrm{Cl}^{-}(a q)+\mathrm{H}_{2}(g)$ Step 1: Identify Oxidation and Reduction Half-reactions

Oxidation half-reaction: Mg --> Mg^2+ (Mg is oxidized) Reduction half-reaction: 2H+ + 2e- --> H2 (H+ ion in HCl is reduced, we consider H+ since it is in aqueous form) Step 2: Balance Atoms in Half-reactions
04

(Balance Mg, Cl, and H atoms in the half-reactions) Oxidation: Mg --> Mg^2+ Reduction: 2H+ + 2e- --> H2 Step 3: Balance Charge Using H2O, H+, and e-

Oxidation: Mg --> Mg^2+ + 2e- Reduction: 2H+ + 2e- --> H2 Step 4: Select coefficients to balance the number of electrons
05

No change as the charges are balanced for both half-reactions. Step 5: Add the two balanced half-reactions

The balanced equation for reaction b: Mg + 2H+ + 2Cl- --> Mg^2+ + 2Cl- + H2 Reaction c. $\mathrm{Co}^{3+}(a q)+\mathrm{Ni}(s) \rightarrow \mathrm{Co}^{2+}(a q)+\mathrm{Ni}^{2+}(a q)$ Step 1: Identify Oxidation and Reduction Half-reactions
06

Oxidation half-reaction: Ni --> Ni^2+ (Ni is oxidized) Reduction half-reaction: Co^3+ --> Co^2+ (Co is reduced) Step 2: Balance Atoms in Half-reactions

(Balance Ni and Co atoms in the half-reactions) Oxidation: Ni --> Ni^2+ Reduction: Co^3+ --> Co^2+ Step 3: Balance Charge Using H2O, H+, and e-
07

Oxidation: Ni --> Ni^2+ + 2e- Reduction: Co^3+ + e- --> Co^2+ Step 4: Select coefficients to balance the number of electrons

(The least common multiple of the half-reactions' electrons is 2) Oxidation: Ni --> Ni^2+ + 2e- Reduction: 2(Co^3+ + e- --> Co^2+) Step 5: Add the two balanced half-reactions
08

The balanced equation for reaction c: 2Co^3+ + Ni --> 2Co^2+ + Ni^2+ Reaction d. $\mathrm{Zn}(s)+\mathrm{H}_{2} \mathrm{SO}_{4}(a q) \rightarrow \mathrm{ZnSO}_{4}(a q)+\mathrm{H}_{2}(g)$ Step 1: Identify Oxidation and Reduction Half-reactions

Oxidation half-reaction: Zn --> Zn^2+ (Zn is oxidized) Reduction half-reaction: 2H+ --> H2 (H+ ion in H2SO4 is reduced) Step 2: Balance Atoms in Half-reactions
09

(Balance Zn and H atoms in the half-reactions) Oxidation: Zn --> Zn^2+ Reduction: 2H+ + 2e- --> H2 Step 3: Balance Charge Using H2O, H+, and e-

Oxidation: Zn --> Zn^2+ + 2e- Reduction: 2H+ + 2e- --> H2 Step 4: Select coefficients to balance the number of electrons
10

No change as the charges are balanced for both half-reactions. Step 5: Add the two balanced half-reactions

The balanced equation for reaction d: Zn + 2H+ + SO4^2- --> Zn^2+ + SO4^2- + H2

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