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Chemical Analysis

Tests for hydrogen, oxygen, carbon dioxide and chlorine

  • 3 things to know
  • Paper 2

Overview

The burning splint test for hydrogen, the glowing splint test for oxygen, limewater turning milky for carbon dioxide, damp litmus paper bleached white by chlorine, why each test is carried out as it is, and identifying a gas from the result.

What you need to know

Answer each one before you reveal it.

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Key term

Describe the solution used to test for carbon dioxide, how the test is carried out, and how a positive and a negative result are read.

Key term

Describe the test for chlorine gas, the result seen, and why the litmus paper is moistened first.

Key term

Describe the test for hydrogen gas and the result you would see.

Questions from this subtopic

Each one with the model answer underneath.

  1. 1

    Describe the test for hydrogen gas and the result you would see.

    Model answer

    Hold a burning splint at the open end of a test tube of the gas; hydrogen burns rapidly with a squeaky pop.

  2. 2

    A gas in a test tube gives a squeaky pop when a lit splint is held at the open end. Which gas is it?

    Model answer

    It is hydrogen.

  3. 3

    Why is a burning splint rather than a glowing one used to test for hydrogen?

    Model answer

    A flame is needed to ignite the hydrogen so that it burns rapidly and gives the pop.

  4. 4

    Describe the test for oxygen gas and the result you would see.

    Model answer

    Insert a glowing splint into a test tube of the gas; oxygen makes the splint relight.

  5. 5

    A glowing splint bursts back into flame when it is pushed into a test tube of gas. Which gas is present?

    Model answer

    It is oxygen.

  6. 6

    Why must the splint used to test for oxygen be glowing rather than fully alight?

    Model answer

    The observation that shows oxygen is the splint relighting, which cannot be seen if the splint is already burning.

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