Question

Write a balanced half-reaction for the oxidation of chromium ion Cr + 3 to dichromate ion Cr 2 O − 2 7 in basic aqueous solution. Be sure to add physical state symbols where appropriate.

Answer 1

Answer:

14 OH⁻(aq) + 2 Cr³⁺(aq) = Cr₂O₇²⁻(aq) + 7 H₂O(l) + 6 e⁻

Explanation:

In order to balance a half-reaction we use the ion-electron method.

Step 1: Write the half-reaction

Cr³⁺(aq) = Cr₂O₇²⁻(aq)

Step 2: Perform the mass balance, adding H₂O(l) and OH⁻(aq) where appropriate

14 OH⁻(aq) + 2 Cr³⁺(aq) = Cr₂O₇²⁻(aq) + 7 H₂O(l)

Step 3: Perform the electric balance, adding electrons where appropriate

14 OH⁻(aq) + 2 Cr³⁺(aq) = Cr₂O₇²⁻(aq) + 7 H₂O(l) + 6 e⁻