Thursday, July 29, 2010
Friday, July 23, 2010
The hydrocarbon component in petroleum can be classified according to their range of boiling points. These hydrocarbons can be separated by using fractional distillation. Crude oil will be heated up to 400°C and converted to viscous oil into hot vapour and fluid. It enters the fractionating tower and condenses into various components according to their temperature, and some gases are drawn off at the top of the tower. The unvaporized residual oil are collected at the bottom.
Gasoline is the best known petroleum product. The components in gasoline are more suitable to use for fueling an automobile, however rapid burning of gasoline-air mixture causes a hard jerk rather than a smooth push to the piston. So herein lays the problem for further treatment of gasoline.
The octane rating of hydrocarbon can be improved by adding small amount of anti-knocking agents, the most widely used anti-knocking agents are:
Tuesday, July 20, 2010
Soap is an item we use daily. It is made up of salt from strong base and fatty acids (carboxylic acids with long hydrocarbon chain). The structure of soap consists of a non-polar tail and a polar-ionic head. Sodium stearate is the most common component in bar soap.
2CH3(CH2)16CO2-Na+ + Mg2 ---->
Monday, July 19, 2010
The calcium ions in the water are usually originated from limestone and chalk, which is made up of calcium carbonate CaCO3, or from other mineral deposits in the form of calcium sulphate, CaSO4. Dolomite deposits (CaMg(CO3)2) contribute to the magnesium ions in the hard water.
Compared to soft water, hard water does not lather easily with soap or toothpaste. The presence of multivalent cations prevents lathering with soap solutions; instead, scum, a white precipitate is formed. The hardness in water causes water to resist soap by forming scales. For example, sodium stearate reacts with calcium:
2C17H35COONa + Ca2+ --> (C17H35COO)2Ca + 2Na+
Hard water can be defined as temporary hard water and permanent hard water. The temporary hardness in water is caused by a combination of Ca2+ ions and bicarbonate ions. Simple steps such as boiling or adding lime (calcium hydroxide, CaOH) can be used to convert to soft water.
Boiling helps to promote the formation of carbonate from bicarbonate and precipitate calcium carbonate. As a result, the cooled water is softened. The reaction of calcium carbonate CaCO3 being dissolved in water can be seen as below:
CaCO3 + CO2 + H2O < -- > Ca2+ +2HCO3-
Permanent water on the other hand cannot be softened by boiling. The calcium and magnesium sulphates or chlorides present in the water become more soluble as the temperature is raised. Although it is termed “permanent”, this hardness can be removed using water softeners, or ion exchange columns, where the calcium and magnesium ions are exchanged with the sodium ions in the column.
Ion exchange column used for softening hard water.
It is considered preferable to soften hard waters, although they do not bring any adverse health effects. However, hard water often cause calcification- the buildup of calcium in pipes and taps. This clogs pipes and causes leakages and bursts.
Calcification on a water tap.
Thursday, July 15, 2010
6(NH2)2CO → C3H6N6 + 6 NH3 + 3 CO2
There are two steps involved in the reaction. First off, urea is decomposed into cyanic acid and ammonia:
(NH2)2CO → HCNO + NH3
Secondly, the cyanic acid formed polymerizes to form melamine and carbon dioxide:
6 HCNO → C3H6N6 + 3 CO2
The decomposition of urea is an endothermic reaction, while the polymerization of cyanic acid is exothermic. Overall, it is an endothermic process.
Ingestion of melamine causes bladder stones. When combined with cyanuric acid, melamine can form crystals that cause the formation of kidney stones. This will contribute to kidney failure and, ultimately, bladder cancer.