The initial orange solution reversibly turns yellow with the formation of precipitate.
name: Barium nitrate precipitates only in alkaline solutions. The equilibrium between chromate and dichromate solution is shifted by addition of base and acid.
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The occurring process involves the equilibrium between chromate(VI), dichromate(VI) and hydrogen ions. Chemical equilibrium behaves according to the Le Chatelier’s principle. It can be stated as "When a system at equilibrium is subjected to change in concentration, temperature, volume, or pressure, then the system readjusts itself to (partially) counteract the effect of the applied change and a new equilibrium is established." The addition of acid shifts the equilibrium to the right, producing more orange-colored dichromate(VI) ions. The addition of hydroxide ions causes the concentration of hydrogen ions to decrease, and this brings the equilibrium back to the left-hand side, regenerating yellow chromate(VI) ions. Barium nitrate interacts with chromate ions producing insoluble barium chromate while while BaCr2O7 does not precipitate.