C3 - Tests for negative ions

C3 - Tests for negative ions

1. Testing for carbonates - check for CO2

   • You can test to see if a gas is carbon dioxide by bubbling it through limewater. If it is carbon dioxide, the limewater turns cloudy
   • You can use this to test for carbonate ions since carbonate react with dilute acids to form carbon dioxide
     • acid + carbonate = salt + water + carbon dioxide

2. Tests for halides

   • To test for chloride,bromide or iodide, add dilute nitric acid followed by silver nitrate solution
     • Chloride gives a white precipitate of silver chloride
     • Bromide gives a cream precipitate of silver bromide
     • Iodide gives a yellow precipitate of silver iodide.

3. To test for sulphate ions

   • Add dilute HCl followed by barium chloride solution
   • A white precipitate of barium sulphate means the original compound was a sulphate.