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Question
What is Nessler’s reagent?
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Solution
- Nessler's reagent is a solution of mercury(II) iodide (HgI2) in potassium iodide (KI) and potassium hydroxide (KOH) named after the German chemist Julius Nessler.
- Nessler’s reagent is an alkaline solution of K2 HgI4.
- It is used in testing for ammonia, with which it forms a brown colouration or precipitate.
\[\ce{NH3 + 2[HgI4]^2- + 4OH^- → HgO.Hg(NH2) + 7I^- + 3H2O}\]
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Low ammonia: Yellow coloration
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High ammonia: Reddish-brown precipitate
This color change confirms the presence of ammonia.
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