What is urea?
Urea is a very notable organic
compound with chemical formula CO (NH2)2. Urea is also known as carbonyldiamide, carbamide, carbonyldiamine etc.
Urea is considered as the first organic compound that synthesized by Friedrich Ohler, in 1828, from inorganic compounds, NH4CNO.
It is odorless white solid and highly soluble in water. Solubility in
water, 1.08 g/ml at 293K and solubility increase with increasing temperature.
Urea is also soluble in glycerol and ethanol solvent. The solubility of urea in glycerol is 0.5 g/ml and in ethanol is 0.05 g/ml.
The
density of urea solution is 1.31 g / ml. Melting point range of urea 406K to
408K.
Urea is neither acidic nor alkaline and practically
non-toxic. Urea is used in many biological processes in the body.
Urea plays an important role in the metabolism of
nitrogenous compounds by animals. It is the main
nitrogenous substance in the urine of mammals.
The
liver forms it by combining two ammonia molecules with the carbon dioxide
molecule in the urea cycle.
Urea structure and molar mass
Urea
is a covalent compound with molecular formula CO (NH2)2. The exact molar mass
of urea molecule is 60.
The
carbonyl carbon of urea is attached with two amino groups. The carbonyl carbon
and oxygen atom of urea are sp2 hybridized.
Hence
according to VSEPR theory, the urea molecule is planar in the crystal
structure, but the geometry around the nitrogen atoms is pyramidal in the
gas-phase minimum-energy structure.
Urea synthesis
Urea
is prepared on a large scale by reacting liquid ammonia with gaseous CO2 at
408K under 220 atmosphere pressures. The
reaction takes place in two steps.
In the first step ammonium carbamate is produced. Some amount of ammonium carbamate is immediately
decomposed to form urea.
The undecomposed ammonium carbamate is processed separately under reduced pressure to give urea. The overall reaction is exothermic.
2 NH3 + CO2 ⇌ H2N-COONH4 (ΔH= -117kJ/mol at 220 atm. and 408K)
H2N-COONH4
⇌ O=C (NH2)2 +
H2O (ΔH=
+15.5 kJ/mol)
Use of urea as fertilizer in agriculture
Urea
fertilizer is a source of nitrogen and hence it is used predominantly in
agriculture for nutrition of plants.
Urea
is a better fertilizer than either ammonium sulfate or calcium ammonium
nitrate.
This
is because the ammonia liberated by hydrolysis is assimilated by the soil
through the interaction of nitrifying bacteria as in the case of ammonium
sulfate or calcium ammonium nitrate.
Again,
CO2 produced in hydrolysis of urea does not cause any damage to the soil like
sulfate or nitrate ions.
Urea is highly soluble in water and so it is very suitable
for use in fertilizer solutions (mixed with NH4NO3).
As a fertilizer, urea is much more effective than, ammonium sulphate
or calcium ammonium nitrate.
Because
of it contains much higher percentage (46.6%) of nitrogen than either (NH4)2SO4
or calcium ammonium nitrate. Thus, it consumes
the minimum transport per unit of nitrogen nutrients.
Many soil bacteria contain the enzyme urease,
which converts urea to NH3 or ammonium ions (NH4 +) and bicarbonate ions (HCO3−).
Thus urea fertilizers are rapidly converted to ammonium in the soil.
In
grain and cotton crops, urea is often applied at the time of the last
cultivation before planting. In sugarcane
cultivation, urea is applied side by side after planting and applied to each
ratoon crop.
Like most hard fertilizers, storage in a cool,
dry, well-ventilated area is recommended. Besides, there is also no risk
of urea conservation as it is not related to the risk of explosion.
However, it also has a disadvantage. Urea is not as stable as other nitrogenous
fertilizers.
It
decomposes even at low temperatures especially in humid environments leaving
NH3 and CO2.
Besides, the most common contamination of synthetic urea is
burette, which inhibits plant growth. Again, it is harmful to keep urea in
large quantities or near seeds.
- What is urea?
- Urea structure and molar mass
- Urea synthesis
- Use of urea as fertilizer in agriculture
Urea,
urea structure, urea molar mass, urea synthesis, urea use, urea cycle, urea
fertilizer, urea nitrogen,
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