balance chemical equation.20分

This is the equation of a redox reaction. In CE level, redox equations are usually balanced using half-equation method.

The half equation for the reduction of Cl2(g) to Cl^-(aq) :
Cl2(g) + 2e^- → 2Cl^-(aq) ...... (*)

The half equation for the oxidation of Cl2(g) to ClO3-(aq) in an alkaline solution :
Cl2(g) + 12OH^-(aq) → 2ClO3^-(aq) + 6H2O(l) + 10e- ...... (#)

5(*) + (#), and eliminate 10e^- on the both sides :
6Cl2(g) + 12OH^-(aq) → 10Cl^-(aq) + 2ClO3^-(aq) + 6H2O(l)

To simplify the above equation, divide all coefficients on the both sides by 2. The balanced ionic equation is :
3Cl2(g) + 6OH^-(aq) → 5Cl^-(aq) + ClO3^-(aq) + 3H2O(l)

Add the dummy ions (6 Na+) to both sides of the equation :
3Cl2(g) + 6Na+(aq) + 6OH^-(aq) → 5Na+(aq) + 5Cl^-(aq) + Na+(aq) + ClO3^-(aq) + 3H2O(l)

Combine the positive and negative ions to write the full equation :
3Cl2(g) + 6NaOH(aq) → 5NaCl(aq) + NaClO3(aq) + 3H2O(l)

2009-11-16 00:10:33 補充：
在酸性溶液才會用 H^+ 來平衡，但現在用鹼性溶液，所以要用 OH^- 來平衡。

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