GCSE Science | Chemical Analysis

Testing for gases

• oxygen - use a glowing splint - splint will relight
• hydrogen - use a burning splint - listen for a squeaky pop
• carbon dioxide - add limewater to a test tube, bubble carbon dioxide into test tube - turns cloudy if CO₂ is present
• chlorine - use damp red litmus paper - litmus paper will turn colourless
• ammonia - use red litmus paper - litmus paper will turn blue

Conducting a flame test

• A platinum or nichrome wire is dipped into concentrated hydrochloric acid to remove any impurities.
  • nichrome wire is inert (unreactive) and has a high melting point
• The wire is dipped into the salt being tested so some salt sticks to the end.
• The wire and salt are held in a burning bunsen burner flame.
• Observe the colour

Testing for metal ions (flame tests)

• Lithium: red
• Sodium: yellow
• Potassium: lilac
• Calcium: orange-red
• Copper: green

Testing for metal ions using sodium hydroxide

• add sodium hydroxide and it forms these precipitates
• Aluminium: white
• Calcium: white
• Magnesium: white
• Copper(II): blue
• Iron(II): green
• Iron(III): brown
• Zinc: white and dissolves