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Reviewed CSCA Chemistry question · Standard

A student generates a gas by adding dilute sulfuric acid to solid sodium sulfite. Which test correctly identifies the gas produced?

  1. The gas turns limewater milky.
  2. The gas relights a glowing splint.
  3. The gas bleaches damp litmus paper.
  4. The gas gives a popping sound with a lighted splint.
Show the answer and explanation

Correct answer

A. The gas turns limewater milky.

Principle or equation

Sodium sulfite reacts with dilute acid to produce sulfur dioxide gas (SO2). Sulfur dioxide turns limewater (calcium hydroxide solution) milky due to formation of calcium sulfite precipitate.

Why this answer is correct

The reaction: Na2SO3(s) + H2SO4(aq) → Na2SO4(aq) + SO2(g) + H2O(l). SO2 is a colorless gas with a pungent smell and turns limewater milky.

Example

In the lab, SO2 is tested by bubbling it into limewater, which becomes cloudy.

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