Question

A compound was found to be soluble in water. It was also found that addition of acid to an aqueous solution of this compound resulted in the formation of carbon dioxide. Which one of the following cations would form a precipitate when added to an aqueous solution of this compound?
a. NH4
b. K
c. Cr
d. Rb
e. Na

Answer 1

Answer:

c. Cr

Explanation:

$Cr^3+(aq) + CO_3^2-(aq) ------------> Cr_2CO_3(s)$

The compound is containing $CO_3^2-$ ion.

If acid reacts with it, CO_2 evolves.

$H^+ + CO_3^2- ----------> H_2O + CO_2$

therefore,  Cr would form a precipitate when added to an aqueous solution of this compound. Cr2CO3 is the precipitate.