79. After filtering out excess solid, a student adds HCl to the solution. He the

Question

79. After filtering out excess solid, a student adds HCl to the solution. He then adds a small amount of
CaSO4 , which dissolves completely. Which of the following also occurs in the new solution?
A. Some Ca(IO3)2 precipitates when the CaSO4 is added.
B. Undissociated HIO3 increases when the HCI is added.
C. Aqueous IO3- decreases when CaSO4 is added.
D. Aqueous Ca2+ decreases when CaSO4 is added.

Can someone please explain how to figure this problem out. What is the thought process behind it?

Thank you!

Explanation / Answer

the answer is (B) since when HCl is added, the concentration of hydrogen ion increases in the solution. Following the Le-Chatelier's principle, equilibrium of reaction (2) shifts in right side and forward reaction is favored. more hydrogen ions combine with iodate ions to give undissociated HIO3 such that the effect of increase in hydrogen ion concentration is reduced. note that the effect of increase in concentration of hydrogen ion can be reduced only when it is reduced, and it is reduced when reaction (2) progresses in forward direction. hence Undissociated HIO3 increases when the HCI is added.

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