What is the oxidation state of chromium in potassium dichromate, K2Cr2O7?
Answer and explanation
Correct answer: B. +6
- Step 1: Assign known oxidation numbers: K = +1, O = -2.
- Step 2: Set up equation for neutral molecule: 2(+1) + 2(Cr) + 7(-2) = 0.
- Step 3: Simplify: +2 + 2(Cr) - 14 = 0, so 2(Cr) - 12 = 0.
- Step 4: Solve for Cr: 2(Cr) = +12, so Cr = +6.
Answer
+6.
Why not the others: '+3' is the common reduced oxidation state of chromium ions (Cr^3+); '+7' is the oxidation state of manganese in permanganate; '+4' miscounts oxygen contributions.
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