Test 1Add dilute sodium hydroxide and a little aluminium powder. If a nitrate is present, ammonia gas is produced. The gas can be identified as it turns moist red litmus paper blue.
- About 2cm3 of dilute sulphuric acid is added into the solution that wants to be tested and then followed by 2cm3 iron (II) sulphate solution.
- A few drops of concentrated sulphuric acid are carefully drop through the inclined side of the test tube without shaking the test tube.
- A brown ring will form in the middle of the solution.
- Explanation: Iron (II) sulphate reduce nitric acid (from the reaction between nitrate ion and concentrated sulphuric acid) to nitrogen monoxide. Afterwards, nitrogen monoxide combines with iron (II) sulphate to form the compound FeSO4.NO which is brown in colour (brown ring).