A white solid is known to be either barium oxide (BaO) or barium sulfate (BaSO4). Which test would best distinguish between them?
Show the answer and explanation
Correct answer
B. Add water and test the pH of the resulting solution.
Principle or equation
Basic oxides react with water to form alkaline solutions, while insoluble sulfates do not react appreciably with water. Therefore, testing the pH of an aqueous suspension can distinguish a basic oxide from an insoluble sulfate.
Why this answer is correct
BaO is a basic oxide that reacts with water to form barium hydroxide, producing an alkaline solution (pH > 7). BaSO4 is insoluble and does not react with water, so the pH remains near 7. Thus, adding water and testing pH distinguishes them.
Example
If a small amount of the white solid is stirred into water and the pH is measured, a pH of about 12 indicates BaO, while a pH near 7 indicates BaSO4.
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