Concept:Chromate (\(CrO_4^{2-}\), yellow) and Dichromate (\(Cr_2O_7^{2-}\), orange) ions exist in a pH-dependent chemical equilibrium.
Formula:$$ 2CrO_4^{2-} + 2H^+ \rightleftharpoons Cr_2O_7^{2-} + H_2O $$
Solution:- Potassium chromate (\(K_2CrO_4\)) is stable in neutral or alkaline solutions.
- When an acid is added, the concentration of \(H^+\) ions increases.
- According to Le Chatelier's Principle, the equilibrium shifts to the right to consume the added \(H^+\) ions.
- This condenses two chromate ions into one dichromate ion (\(Cr_2O_7^{2-}\)), changing the solution color from yellow to orange.
- Therefore, the product is Potassium dichromate (\(K_2Cr_2O_7\)).
Why other options are incorrect:- The reaction fundamentally alters the oxoanion of chromium; it does not simply form random salts like sulfates or chlorides.
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