Question

What is the colour when hydrogen peroxide react with potassium chromate?

Answer 1

Answer on Question#40598-Chemistry-Other

Question

What is the colour when hydrogen peroxide reacts with potassium chromate?

Answer

Potassium chromate solution is yellow. When reacting with hydrogen peroxide the latter is oxidized forming water and oxygen gas, and potassium chromate is reduced in generally from $\mathrm{Cr}^{+6}$ to $\mathrm{Cr}^{+3}$. The exact reduction product and consequently the colour depends on the solution pH.

pH < 7 (acidic):

$$\mathrm{K_2CrO_4 + 2H_2O_2 + H_2SO_4 \rightarrow CrO_5 + 3H_2O + K_2SO_4}$$

yellow solution  dark blue solution

But the blue chromium(VI)peroxide is an unstable compound and after a few seconds it decomposes to turn green as chromium(III) compounds are formed, so the reaction may be written as follows:

$$2\mathrm{K_2CrO_4 + 5H_2SO_4 + 5H_2O_2 \rightarrow Cr_2(SO_4)_3 + 2K_2SO_4 + 4O_2\uparrow + 10H_2O}$$

yellow solution  green solution

pH = 7 (neutral):

$$2\mathrm{K_2CrO_4 + 9H_2O_2 \rightarrow 2Cr(OH)_3\downarrow + 4KOH + 6O_2\uparrow + 4H_2O}$$

yellow solution  yellowish-green precipitate

pH > 7 (basic):

$$2\mathrm{K_2CrO_4 + 2KOH + 3H_2O_2 \rightarrow 2K_3CrO_3 + 3O_2\uparrow + 4H_2O}$$

yellow solution  light-green solution