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Question
You are provided with two reagent bottles marked A and B. One of which contains NH4OH solution and the other contains NaOH solution. How will you identify them by a chemical test?
Solution
Reagent bottles A and B can identified by using calcium salts such as Ca(NO3)2.
When NaOH is added to Ca(NO3)2, Ca(OH)2 precipitates as a white precipitate that is sparingly soluble in excess of NaOH.
\[\ce{Ca(NO3)2 + 2NaOH -> Ca(OH)2 + 2NaNO3}\]
whereas, on addition of NH4OH to calcium salts, no precipitation of Ca(OH)2 occurs even with an excess of NH4OH because the concentration of OH−ions from the ionization of NH4OH is so low that it cannot precipitate the calcium hydroxide.
So the reagent bottle which gives white precipitate is NaOH and the other is NH4OH.
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