Which of the following salts is slightly soluble in water?

Analysis

The question asks us to identify which of the given salts is "slightly soluble" in water. Solubility refers to the ability of a substance to dissolve in a solvent. In chemistry, we categorize salts based on their solubility rules.

Concept Explanation

To solve this, we apply the general solubility rules for inorganic salts:

1. Sodium (Na⁺) salts: Almost all sodium salts (like $Na_2CO_3$) are highly soluble in water.
2. Chlorides (Cl⁻): Most chlorides are soluble, but there are exceptions. Silver chloride ($AgCl$) and Lead(II) chloride ($PbCl_2$) are generally considered insoluble (they form precipitates).
3. Sulfates ($SO_4^{2-}$): Most sulfates are soluble, but there are notable exceptions like Barium sulfate ($BaSO_4$), Lead sulfate ($PbSO_4$), and Calcium sulfate ($CaSO_4$).

"Slightly soluble" refers to substances that do not dissolve completely but are not as insoluble as a precipitate like $AgCl$. $CaSO_4$ is a classic example of a salt that is sparingly or slightly soluble in water.

Step-by-Step Solution

• Option A ($AgCl$): This is an insoluble salt. It is used in qualitative analysis to test for chloride ions because it forms a white precipitate.
• Option B ($CaSO_4$): Calcium sulfate is known to be sparingly (slightly) soluble in water. It is often used in the context of "temporary hardness" in water because it dissolves only to a small extent.
• Option C ($Na_2CO_3$): Sodium carbonate is highly soluble in water. It is a common washing soda used in laboratories and homes.
• Option D ($PbCl_2$): Lead(II) chloride is considered insoluble at room temperature, though its solubility increases significantly in hot water.

Comparing these, $CaSO_4$ is the most accurate fit for the term "slightly soluble" in the context of standard JAMB chemistry curriculum.

Conclusion

While $PbCl_2$ has some solubility, $CaSO_4$ is the standard textbook example for a slightly soluble sulfate.

Exam Tip

Remember the acronym "SNAP" for solubility: Sodium, Nitrate, Ammonium, and Potassium salts are always soluble. When you see these in an option, you can usually rule them out if the question asks for an insoluble or slightly soluble salt!