The apparatus is warmed and a gas that smells sharp turns the damp litmus paper blue. Use the diagram to state which ion this test shows is present in the f...
Question 1 Report
The apparatus is warmed and a gas that smells sharp turns the damp litmus paper blue. Use the diagram to state which ion this test shows is present in the fertiliser.
Answer Details
A sharp-smelling gas that turns damp litmus paper blue is ammonia, since ammonia is the only common alkaline gas. Ammonia is only released when an alkali is warmed with a salt containing the ammonium ion, so this test shows that the ammonium ion is present in the fertiliser:
\[ \mathrm{NH_4^{+} + OH^{-} \rightarrow NH_3 + H_2O} \]
The sulfate ion is detected quite differently, by adding acidified barium chloride solution and looking for a white precipitate. The chloride ion needs acidified silver nitrate solution, which gives a white precipitate. The nitrate ion also gives ammonia, but only after aluminium foil and sodium hydroxide are added and warmed, and no aluminium is used here.
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