Test for gases

Edexcel Unit 2

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  • Created by: Abigail
  • Created on: 15-01-10 02:38

Tests for gases 1

Test for hydrogen.

Test: Ignite the gas

Observation: burns with squeaky pop

Test for Oxygen

Test: place a glowing wooden splint in the gas

Observation: Relight splint.

Test for carbon dioxide

Test: bubble gas through lime water

Observation: lime water goes cloudy/milky

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Test for gases 2

Test for Ammonia

Test: place damp red litmus paper into gas

Observation: litmus paper goes blue

Test for Nitrogen dioxide

Test: observe colour

Observation: gas is brown

Test for chlorine

Test: place damp litmus paper in the gas

Observation: bleaches rapidly the litmus paper

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Test for gas 3

Test for Hydrogen chloride

Test 1: place damp blue litmus paper into gas

Observation: turns blue litmus paper red

Test 2: place the stopper from a bottle of concentrated ammonia in the gas

Observation: white smoke(ammonium chloride) is formed

Test for Sulphur dioxide

Test: place filter paper soaked in potassium dichromate solution in the gas.

Observation: colour changes from orange to green

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Flame test

Clean platinum or nichrome wireis dipped into concentrated hydrochloric acid, then into the solid to be tested and finally into the hottest part of the Bunsen flame.

The concentrated hydrochloric acid convert some of the unknown solid into chlorides.

Chlorides are more volatile than other salts, so some of the unknown goes into gas phase when heated in the hot flame.

Colours of the flame test are produced through the excitation of electrons to higher energy levels, they become unstable and falls to the ground state. Through the process of falling it emits light of colour specific to the metal present in the compound.

  • The flame test is the only test for group 1
  • Flame test cannot be used on mixtures as the colour produced by one of the ions will mask the colour produced by the other metal ions.

Li+ (crimson) , Na+ (Yellow), K+ (Lilac), Ca 2+ (Yellow-red), Sr 2+ (Red), Ba 2+ (pale green)

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