Balance each of the following half-reactions, assuming that they occur in basic solution.Express...

Question:

Balance each of the following half-reactions, assuming that they occur in basic solution. Express your answer as a chemical equation including phases.

1) {eq}CrO_4^{2-} (aq) <=> Cr(OH)_3 (s) {/eq}

2) {eq}H_2O (l)<=>H_2 (g) {/eq}

3) {eq}Cr^{3+} (aq) <=> Cr^{2+} (aq) {/eq}

4) {eq}BiO^+ (aq) <=> Bi (s) {/eq}

Redox Reaction:


A redox reaction involves electron transfer between two species. The species that loses/gains electrons is oxidized/reduced respectively. Each of these processes can be written in an oxidation or reduction half-reaction that is balanced in acidic, basic or neutral solution.

Answer and Explanation: 1


To identify the oxidation state that is changing, we need to remember these rules:

  • A neutral element on its own has an oxidation number of zero.
  • The sum of the oxidation numbers for a neutral molecule must be zero.
  • The sum of the oxidation numbers for an ion is equal to the net charge on the ion.
  • In a compound: hydrogen prefers +1, oxygen prefers -2, fluorine prefers -1.

To balance half-reactions in basic solution we can follow this general guideline:

a) Balance elements other than hydrogen and oxygen.

b) Determine the element changing oxidation state on both sides of the equation.

c) Add electrons to the appropriate side of the equation to show this change in oxidation state.

d) Add {eq}OH^- {/eq} to the appropriate side to balance charge.

e) Add {eq}H_2O {/eq} to the appropriate side to balance oxygen.

Question 1)

  • Chromium is reduced here from +6 in chromate anion to +3 in chromium (III) hydroxide:

{eq}4H_2O (l) + CrO_4^{2-} (aq) + 3e^- \rightarrow Cr(OH)_3 (s) + 5OH^- (aq) {/eq}

Question 2)

  • Hydrogen is reduced from +1 in water to zero in hydrogen gas:

{eq}2H_2O (l) + 2e^- \rightarrow H_2 (g) + 2OH^- (aq) {/eq}

Question 3)

  • Chromium, is reduced from +3 in the aqueous ion to +2 in the aqueous ion:

{eq}Cr^{3+} (aq) + e^- \rightarrow Cr^{2+} (aq) {/eq}

Question 4)

  • Bismuth is reduced from +3 to zero in bismuth metal:

{eq}H_2O (l) + BiO^+ (aq) +3e^- \rightarrow Bi (s) + 2OH^- (aq) {/eq}


Learn more about this topic:

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Balancing Redox Reactions and Identifying Oxidizing and Reducing Agents

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Chapter 10 / Lesson 13
173K

Learn about oxidizing and reducing agents, how to find them, and how to identify them in redox reactions. Learn about the different types of redox reactions and how to identify a redox reaction.


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