Question

Which salt is least soluble in water at 20°C?

a) Sodium chloride (NaCl)
b) Sodium sulfate (Na2SO4)
c) Potassium chloride (KCl)
d) Calcium carbonate (CaCO3)

Answer 1

Calcium carbonate (CaCO3) is the least soluble salt in water at 20°C because carbonates are typically insoluble except for those of the ammonium ion and alkali metals.

Step-by-step explanation:

The question asks which salt is least soluble in water at 20°C among Sodium chloride (NaCl), Sodium sulfate (Na2SO4), Potassium chloride (KCl), and Calcium carbonate (CaCO3). According to solubility rules, carbonates are generally insoluble except for those of the ammonium ion and the alkali metals. Considering the provided salts, Calcium carbonate, belongs to the category of carbonates that are not alkali metal carbonates and is therefore typically insoluble in water. The solubility of calcite (a form of CaCO3) in water is 0.67 mg/100 mL at 20°C, corresponding to a very low solubility product constant (Ksp) of 4.5 × 10−9, signifying low solubility. Therefore, CaCO3 is the least soluble of the given salts at 20°C.

Answer 2

Calcium carbonate (CaCO3) is the least soluble in water at 20°C among the given options, with a solubility of only 0.67 mg per 100 mL.

Step-by-step explanation:

The question asks about the solubility of salts in water at 20°C. Based off the provided solubility rules and given data, we know that salts containing carbonate ions (except for those combined with ammonium ions and alkali metals) are typically insoluble. Therefore, of the options given, calcium carbonate (CaCO3) is least soluble in water at 20°C. For example, the solubility of calcite, which is one crystalline form of CaCO3, is only 0.67 mg per 100 mL of water. This is significantly less than the solubility of salts like sodium chloride (NaCl) and sodium sulfate (Na2SO4), which are both highly soluble ionic compounds.