Urea
Formula
CO(NH2)2
Preparation
Urea can be prepared by converting ammonium carbamate into urea and water. This is similar to the classical Wöhler synthesis. Ammonia reacts with carbon dioxide to form ammonium carbamate, and when the mixture is heated, it breaks down into urea. The heat released in the first step drives the second reaction, which is why this method is used industrially.
Tests for Purity
- Appearance: White solid.
- Solubility: Soluble in water; insoluble in ethanol.
- Alkalinity: A 5% solution should not require more than 0.04 ml of 0.01M HCl to neutralize.
- Biuret Test: Urea reacts with biuret reagent (alkaline copper sulfate) producing an orange color. The intensity is compared with a standard (should be less than 10 ml of 0.02M biuret solution).
- Heavy Metals: Should be less than 20 ppm.
Assay
Urea is assayed indirectly. It reacts with sulfuric acid to form ammonium sulfate. The ammonium sulfate is treated with excess sodium hydroxide, and the ammonia produced is distilled and collected. The distillate is titrated with 0.1M HCl.
Conversion factor: 1 ml of 0.1M HCl ≡ 0.003003 g urea
Uses
- Most commonly used nitrogen fertilizer worldwide.
- Important industrial raw material for various chemical processes.
- Contains 46% nitrogen, making it a highly concentrated fertilizer.
- Available as free-flowing granules (prills) for agricultural use.
Detailed Notes:
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