When aqueous solutions of Ba(NO3)2 and K2CrO4 are mixed, a yellow precipitate is

Question

When aqueous solutions of Ba(NO3)2 and K2CrO4 are mixed, a yellow precipitate is observed. This is due to the formation of insoluble BaCrO4.

Rxn 2 Ba2+ (aq) + CrO42 (aq) BaCrO4 (s)

When aqueous HCl is added the yellow precipitate dissolved and an orange solution is formed.

1) if more than one equilibrium are involved, how would this shift affect the other equilibrium? The concentration of which species is/are expected to be affected and how owuld it/they be affected (increase or decrease)

2) would the change in concentration be observable

3) is the above consistent with what was actually observed?

Explanation / Answer

The two equilibriums:

Ba2+ (aq) + CrO42 (aq)--> BaCrO4 (s)

H+ (aq) + CrO42 (aq) --> HCrO42- (s)

note that addition of H+ favour acid formation, which will also favour more BaCrO4 dissolution

Q2.

the change in concentration is likely to be observed, since the acid present is a weak, yet can be measured

Q3.

Yes, since a change in color toward yellow will mean that more acid is being formed than the solid precipitate

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