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An organic compound with identical empirical and molecular formulas consists of 20% carbon, 6.7% hydrogen, 46.7% nitrogen, and the remainder as oxygen. When heated, it releases ammonia and leaves behind a solid residue. This residue produces a violet color when treated with an alkaline copper sulfate solution. Identify the compound.

1. Ammonium carbamate
2. Ammonium formate
3. Hydroxylamine
4. Urea

Correct answer: Urea

Solution

Mole ratios C:H:N:O = 20/12 : 6.7/1 : 46.7/14 : 26.6/16 = 1:4:2:1, giving CH4N2O. On heating it releases ammonia and the residue (biuret) gives a violet color with alkaline copper sulfate, which identifies the compound as urea.

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