Which of the following compounds will have the highest molar solubility in pure water?

• A. BaSO_4
• B. AgCl
• C. NaNO_3
• D. CaCO_3

Answer: (C)

Verified step by step guidance

1. Step 1: Understand that molar solubility refers to the number of moles of a compound that can dissolve in a liter of water to form a saturated solution. It depends on the compound's solubility product constant, \(K_{sp}\), and the nature of the compound (ionic vs. molecular).
2. Step 2: Recognize that \(BaSO_4\), \(AgCl\), and \(CaCO_3\) are sparingly soluble salts with relatively low \(K_{sp}\) values, meaning they dissolve only slightly in water, producing low molar solubility.
3. Step 3: Note that \(NaNO_3\) is a highly soluble ionic compound that dissociates completely in water, so its molar solubility is very high compared to the other salts listed.
4. Step 4: To compare quantitatively, you would look up or be given the \(K_{sp}\) values for the sparingly soluble salts and calculate their molar solubility using the expression \(K_{sp} = [M^{n+}]^m [X^{m-}]^n\), where \(M\) and \(X\) are the ions formed upon dissolution.
5. Step 5: Since \(NaNO_3\) is a strong electrolyte and dissolves completely, its molar solubility is much higher than the others, which is why it has the highest molar solubility in pure water.