Urea

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Urea or carbamide, is an organic compound commonly used as a fertilizer. It has the chemical formula (NH2)2CO. Urea was the first organic chemical produced from inorganic chemicals, a breakthrough in chemistry, which proved organic substances can be produced from inorganic substances, disproving the notion of vitalism.

Properties

Chemical

Thermal decomposition of urea produces ammonium isocyanate, who in turn yields isocyanuric acid.

NH2CONH2 → NH4NCO → HNCO + NH3

Urea is a weak organic base. It forms salts with strong acids. Despite its two amino groups, it acts as a monoprotic base, only accepting one H+ cation. With diprotic acids such as sulfuric, urea forms two types of salts: monocarbamide dihydrosulfate (carbamonium bisulfate, analogous to inorganic bisulfates) and dicarbamide dihydrosulfate (carbamonium sulfate, analogous to inorganic sulfates).

A frequent contaminant of urea is Biuret. A high concentration of Biuret mitigates against using urea as a crop fertilizer, but makes it more valuable as an animal feed additive.

Physical

Urea is a white crystalline substance. Its melting point is between 133-135 °C. Urea is soluble in water (107.9 g/100 ml at 20 °C) and when dissolved, it is neutral on the pH scale. Urea is soluble in glycerol (500 g/L) and slightly less soluble in ethanol.

Availability

Urea is available as a fertilizer, either pure or mixed with other substances. It can be very cheaply purchased online, often at less than $5/kg.

ScienceCompany sells 500g of lab grade urea at 16.95 $.

Ebay has many listings for urea as a lab chemical and as fertilizer

Preparation

Urea was first synthesized by reacting silver cyanate with ammonium chloride.

AgNCO + NH4Cl → (NH2)2CO + AgCl

Industrially it is produced by the thermal decomposition of ammonium carbamate.

It can also be produced from the reaction of phosgene and ammonia

COCl2 + 4 NH3 → (NH2)2CO + 2 NH4Cl

Reactions

Projects

Handling

Safety

Urea is non-toxic, though is may cause irritations to sensitive tissues. It may corrode metallic surfaces, even the more resistant forms of stainless steel.

Storage

Urea doesn't require any special storage, and can be safely stored in glass, metal, plastic or ceramic containers.

Disposal

As urea is a good fertilizer, it can be safely dumped in the soil, although it's recommended to avoid dumping it in water reservoirs to prevent the growth on unwanted algae. It can also be used to as a nitrogen source for aerobic bacteria in the conversion of sawdust to compost.

References

Relevant Sciencemadness threads