In the following chemical reaction: 2𝐻𝐶𝑟𝑂−4(𝑎𝑞) + 8𝐻 + (𝑎𝑞) + 3𝐶𝑙𝑂−3 (𝑎𝑞) → 2𝐶𝑟3+(𝑎𝑞) + 5𝐻2𝑂(𝑙) + 3𝐶𝑙𝑂−4(𝑎𝑞) What element is being reduced?

Answer 1

Let's assign oxidation numbers to all species, on both the left and right side of the equation.

2HCrO₄^- + 8H⁺(aq) + 3ClO₃^-(aq) ==> 2Cr³⁺(aq) + 5H₂O(l) + 3ClO₄^-

+1 +6 -2.....+1..............+5 -2..................+3................................+7 -2 ......Oxidation numbers

So, Cr goes from +6 on the left to +3 on the right. It was reduced.

Cl goes from +5 on the left to +7 on the right. It was oxidized.