Question

What is the oxidation state of chromium in K₂Cr₂O₇?

• A. +6
• B. +3
• C. +2
• D. 0

Hint:

In ionic compounds, the sum of the oxidation states of all elements equals the net charge of the molecule. Use this principle to find unknown oxidation states.

Answer 1

The Correct Option is A

The compound given is K₂Cr₂O₇ (potassium dichromate). To determine the oxidation state of chromium (Cr), we need to follow the steps below:
1. Assign Oxidation States: - Potassium (K) has a charge of \( +1 \) because it is an alkali metal. - Oxygen (O) generally has an oxidation state of \( -2 \) in most compounds, including this one. 2. Set up the equation: - Let the oxidation state of chromium be \( x \). - In K₂Cr₂O₇, we have 2 potassium ions (\( +2 \)), 2 chromium ions (\( 2x \)), and 7 oxygen atoms (\( 7 \times -2 = -14 \)). - The total charge on the compound is zero, so the sum of all oxidation states must equal zero: \[ 2 \times (+1) + 2x + 7 \times (-2) = 0 \] \[ 2 + 2x - 14 = 0 \] \[ 2x = 12 \] \[ x = +6 \] 3. Conclusion: - The oxidation state of chromium in \( \text{K}_2\text{Cr}_2\text{O}_7 \) is \( +6 \).