When dilute hydrochloric acid is added to sodium chromate solution th…

The correct answer is option 4. orange. 

Let us break down the process and the color change in detail when dilute hydrochloric acid (\(HCl\)) is added to a sodium chromate (\(Na_2CrO_4\)) solution:

Sodium Chromate (\(Na_2CrO_4\))

Sodium chromate is a salt that dissociates in water to produce chromate ions (\(CrO_4^{2-}\)). The chromate ion has a yellow color in aqueous solution.

Hydrochloric Acid (\(HCl\)):

Hydrochloric acid is a strong acid that dissociates in water to produce hydrogen ions (\(H^+\)) and chloride ions (\(Cl^-\)).

Chemical Reaction:

When hydrochloric acid is added to a sodium chromate solution, the following chemical reaction occurs:

\(2 \text{CrO}_4^{2-} + 2 \text{H}^+ \rightarrow \text{Cr}_2\text{O}_7^{2-} + \text{H}_2\text{O}\)

In this reaction:

Chromate ions (\(CrO_4^{2-}\) are converted into dichromate ions (\(Cr_2O_7^{2-}\)). The chromate ions are yellow, while the dichromate ions are orange.

Detailed Steps of the Color Change:

Initial State:

Sodium Chromate Solution: Contains \(CrO_4^{2-}\) ions, which impart a yellow color to the solution.

Addition of Hydrochloric Acid:

Acidic Environment: The hydrogen ions (\(H^+\)) from the hydrochloric acid react with the chromate ions. The acidic conditions shift the equilibrium towards the formation of dichromate ions.

Reaction and Color Change:

The reaction transforms yellow chromate ions (\(CrO_4^{2-}\)) into orange dichromate ions (\(Cr_2O_7^{2-}\)). The solution changes color from yellow to orange as a result of this conversion.

Summary:

In a neutral or basic environment, sodium chromate gives a yellow solution due to the presence of \(CrO_4^{2-}\) ions. When hydrochloric acid is added, the acidic conditions lead to the formation of \(Cr_2O_7^{2-}\) ions, which results in an orange-colored solution.