如何test ammonium ions?

When ammonium ion is heated with an alkali (OH- ion), ammonia gas is formed which turns moist red litmus paper to blue.
NH4+(aq) + OH-(aq) → NH3(g) + H2O(l)

To test for ammonium ion:
The unknown solution is mixed with sodium hydroxide solution in a test tube. Heat the mixture with a Bunsen flame. If a pungent gas is given off which turns moist red litmus paper to blue, the unknown solution contains ammonium ion.
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