Question

a. A solution of potassium dichromate is reduced to chromium(III) ions by zinc metal in the presence of an acid causing the solution to change in color from orange to green. What is the oxidation state of the chromium in the potassium dichromate molecule?

Answer 1

Explanation:

It is known that molecular formula of potassium dichromate is $K_{2}Cr_{2}O_{7}$. As potassium has an oxidation state of +1 and an oxygen atom has an oxidation state of -2.

Let the oxidation state of chromium is x. Therefore, calculate the oxidation state of chromium as follows.

                  $K_{2}Cr_{2}O_{7}$ = 0          (as the molecule is neutral)

                  $(2 \times 1) + 2x + (-2 \times 7)$ = 0

                            2 + 2x - 14 = 0

                                    x = +6

Thus, we can conclude that the oxidation state of the chromium in the potassium dichromate molecule is +6.