Question

Lead pigments were used in water colour painting which turned black after prolonged to an air pollutant the original color was restored by using H2O2 which pollutant turned the painting black?

Answer 1

Task:

Lead pigments were used in water colour painting which turned black after prolonged to an air pollutant the original color was restored by using H2O2 which pollutant turned the painting black?

Answer:

The chemical formula for Lead pigments is $\mathrm{PbCO_3 \cdot Pb(OH)_2}$.

There is always some $\mathrm{H_2S}$ in air. Because of reaction between $\mathrm{H_2S}$ and lead pigments the color turns black.

The chemical equation for this reaction is

$$\mathrm{PbCO_3 \cdot Pb(OH)_2(s) + 2H_2S(g) = 2PbS(s) + 3H_2O(l) + CO_2(g)}$$

PbS is black.

To restore the original color $\mathrm{H_2O_2}$ is used according to the reaction

$$\mathrm{PbS(s) + 4H_2O_2(aq) = PbSO_4(s) + 4H_2O(l)}$$

$\mathrm{PbSO_4}$ is white.

The pollutant that turned the painting black is $\mathrm{H_2S}$