The urea fertiliser is manufactured slightly differently. Urea is made from the reaction of ammonia and carbon dioxide. The ammonia and carbon dioxide are fed into a reactor at a high pressure and temperature. The reaction of the carbon dioxide and the ammonia produces ammonium carbamate. The ammonium carbamate is then decomposed to produce urea and water. [3]
2NH3 + CO2 →NH2COONH4
Ammonia + Carbon Dioxide → Ammonium Carbamate
NH2COONH4 → NH2CONH2 + H2O
Ammonium Carbamate → Urea + Water
The advantages and disadvantages of the fertilisers:
Advantages of urea:
- Urea can be applied to soil as a solid or solution or to certain crops as a foliar spray.
- Urea usage involves little or no fire or explosion hazard.
- Urea manufacture releases few pollutants to the environment.
- Urea has the highest nitrogen content, at 46%. This percentage is much higher than other nitrogenous fertilizers available in the market.
- The cost of production of urea is low because carbon dioxide, required for its manufacture, can be easily obtained from crude naphtha.
Disadvantages of urea:
- Urea is very soluble in water, and hygroscopic water (hygroscopic water creates a thin layer surrounding individual soil particles, which makes water unavailable to plants), and it therefore requires better packaging quality.
- It is not as stable as other solid nitrogenous fertilizers. It decomposes even at room temperatures, particularly in a humid atmosphere. It releases ammonia and carbon dioxide into the air.
- If urea contains impurities more than 2%, it cannot be used as a fertilizer, since the impurities are toxic to certain crops, particularly citrus. [4]
Advantages of ammonium nitrate:
- It is one of the cheapest crop nourishing fertilisers.
- It is easily available in the markets and agricultural stores.
- It has a high decomposition point of 400 degrees Fahrenheit.
Disadvantages of ammonium nitrate:
- It is very explosive if it comes into contact with fire or high temperature level.
- Its decomposition point is significantly lower when it comes in contact with organic and/or inorganic impurities.
- Storing excessive amounts can also cause problems regarding fire safety. [5]
Advantages of ammonium sulphate:
- It dissolves slowly into the soil, which makes it cheaper than some other fertilisers.
- It maintains healthy nitrogen levels in the soil and, in the case of alkaline soils, helps to maintain a good pH balance.
Disadvantages of ammonium sulphate:
- It can be used as an explosive.
- When used in excess, it can cause a range of undesirable plant conditions such as excessive leaf growth, weak plant bodies, and excessive thatch in lawns. [6]
Specific heat capacity for the acids:
Nitric acid = 1.74 J/g °C
Sulphuric acid = 1.42 J/g °C
How an acid reacts with an alkali in a neutralisation reaction:
An acid and an alkali react to produce salt and water. This is usually an exothermic process. In general, acid and alkali reactions can be simplified to:
OH- + H+ → H2O
Acids are generally pure substances that contain hydrogen ions (H+) or cause them to be produced in solutions. Sulphuric acid is an example of this (H2SO4). In water, it breaks apart into ions:
H2SO4 → H+ + HSO4 -
In general, alkalis are defined as substances that contain the hydroxide ion (OH−) or produce it in solution. One example would be sodium hydroxide (NaOH). To produce hydroxide ions in water, the alkali breaks apart into ions:
NaOH → Na+ + OH-
Therefore, the ions from an acid and an alkali react to cancel each other out and produce a neutral solution. The resultant pH value will generally be pH 7 and this is shown as a green colour on universal indicator paper. [7]
References:
- http://en.wikipedia.org/wiki/Neutralization_(chemistry)
