Question

based on the solubility rules, which one of the following compounds should be insoluble in water?
caco₃
(nh₄)₂co₃
na₂co₃
k₂co₃
kno₃

Explanation:

Step1: Recall solubility rules

Carbonates of alkali - metals (Group 1 elements) and ammonium ($NH_4^+$) are soluble in water. Nitrates ($NO_3^-$) are always soluble in water.

Step2: Analyze each compound

• $\text{CaCO}_3$: Calcium is an alkaline - earth metal. Carbonates of alkaline - earth metals are generally insoluble in water.
• $(NH_4)_2\text{CO}_3$: Ammonium carbonate is soluble because ammonium salts are soluble.
• $\text{Na}_2\text{CO}_3$: Sodium is an alkali - metal. Sodium carbonate is soluble.
• $\text{K}_2\text{CO}_3$: Potassium is an alkali - metal. Potassium carbonate is soluble.
• $\text{KNO}_3$: Nitrates are always soluble.

Answer:

$\text{CaCO}_3$