Reviewed CSCA Chemistry question · Standard

A white solid is known to be either sodium oxide (Na2O) or sodium chloride (NaCl). Which test would best distinguish between them?

Add dilute hydrochloric acid and test for the gas produced.
Add water and test the pH of the resulting solution.
Heat the solid and observe any color change.
Add silver nitrate solution and observe any precipitate.

Show the answer and explanation

Correct answer

B. Add water and test the pH of the resulting solution.

Principle or equation

Sodium oxide is a basic oxide that reacts with water to form sodium hydroxide, producing an alkaline solution (pH > 7). Sodium chloride dissolves to form a neutral solution (pH ≈ 7).

Why this answer is correct

Na2O(s) + H2O(l) → 2NaOH(aq), which gives a basic solution. NaCl dissolves without hydrolysis, giving a neutral solution. Testing pH distinguishes them.

Example

Add a small amount of each solid to separate test tubes with water. Test with pH paper: Na2O gives a high pH (e.g., 13), NaCl gives pH around 7.

This published item includes a stored explanation and passed the platform’s publication workflow. It is independent preparation material, not a claim of an official or recalled examination question.