LEAD POISONING

Lead, which is a metal, has a symbol of Pb that originated from Latin word Plumbum. Lead is a toxic metal that was used in many products such as painted toys and storage batteries. It can also be found in contaminated soil, household dust and drinking water in homes that contained pipes that were connected with lead solder.

By inhaling air, drinking water or touching or swallowing dirt that contains lead can lead to lead poisoning.Lead poisoning can cause many health problems. In adults, lead can increase blood pressure which in turn leads to nerve disorders.It is especially harmful to children. Children who take in huge amounts of lead can cause anemia, muscle weakness and brain damage.This is because lead can inhibit the production of heamoglobin which is needed by human bodies in transporting oxygen and carbon dioxide. Insufficient amount of oxygen in brain can cause brain damage.

As quoted from Bloomberg News, July 2010, excessive levels of lead was found in the blood of 84 children in the county of Heqing, Yunnan, China, due to illegal gold processing operations. The children were diagnosed after the local environmental protection department cracked down on operations that used Cyanide to extract gold from ore in the county. Rising of gold prices had encourage the villagers in the county to begin processing ore in their homes, which then generated lead fumes and poisonous solid waste. More than 4000 poeple in China were poisoned by lead in 2009 and more than 2000 of them were children. China largest lead maker in Henan, Henan Yuguang Gold and Lead Co had closed an outdated plant in October 2009 due to the excessive level of lead found in 1800 of children in the province.

An important way to prevent lead poisoning is to discourage children from eating or chewing on food that may contain lead such as keys, paint chips, lead sinkers used for fishing and lead soldier. Besides, children should be encouraged to wash their hands often, especially before eating and after playing. Food can become contaminated with lead. So, to prevent exposure to lead, avoid eating foods that are cooked or stored in imported pottery. Always wash fruits and vegetables before eating them as they may have lead on them if they were grown in lead contaminated soil.

GASOLINE

We use gasoline everyday- as fuel for cars and various industries. Petroleum can be found in earth’s crust, formed by the decomposition of animal and plant by bacteria over millions of years.

Crude Oil.

Unrefined petroleum appears as a viscous dark-brown liquid, often called crude oil. It is a complex mixture of alkanes, alkenes, cycloalkanes and aromatic compounds. However, the actual compound of petroleum depends on the location.

Fractionation Distillation Tower.

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:

Tetramethyllead Tetraethyllead

2-4g of either these two compound are added into a gallon of gasoline to reduce the hard jerk. However, these compounds are highly toxic and causes serious environment problem. Therefore, unlead gasolines containing methyl tert-butyl ether (MTBE) is used to replace it.

Four Stroke Cycle

The four stages of operation of an internal combustion engine are:

a) Intake- The intake valve opens to let in the gasoline-air mixture.

b) Compression- The two valves are closed during the compression stage.

c) Power- The fuels react and the piston is pushed outward.

d) Exhaust- The exhausted valve open to let gaseous out when the piston travels back up.

Reaction: C8H18 + 25/2 O2 → 8CO2 + 9H2O

Heat is released in the reaction.

SOAP

Bar Soap

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.

C17H35COO-Na+ (Sodium Stearate)

There are three major types of soap, mainly: Lithium soap, which is hard with a high melting point and widely used in car lubricants; Sodium soap, more soluble in water and appearing as common bar soap; and Potassium soap, which has a low melting point and appears in liquid form.

How soap is made.

Soap can be prepared through the saponification process. During the process of soap manufacture, the ester group commonly found in lipids undergo hydrolysis with a strong base. In soap industrial manufacture, tallow (animal fat) or vegetable oil is commonly used to be heated with sodium hydroxide.

C17H35COOC2H5 + NaOH ---> C17H35COO-Na+ + C2H5OH

Once the saponification process is complete, sodium chloride is added into the soap to form a precipitate. Water layer is drawn from the top of the mixture and vacuum distillation method is used to recover the glycerol.

Crude soap that is produced from saponification contains sodium chloride, sodium hydroxide and glycerol. The purification process is repeated by boiling the crude soap curd in water and re-precipitating it with salt. Sand or pumice may be added to produce scouring soap.

The soap formed is made up of polar molecules with negative charges. The long non-polar hydrocarbon chain does not face water molecules but attach to each other via dispersion forces and formed micelles embedded with polar-ionic heads. Its polar-ionic head interacts with water molecules through ion-dipole interactions and H bonds and form negatively-charged spherical surface. Soap micelles repel each other in water due to this negatively-charged surface.

Polar-ionic Head & Non-polar Head Form Micelle.

How soap works.

Non-polar tails and polar-ionic heads of soap make it an excellent emulsifying agent and enable it to remove grease from our hand and clothes. Grease and oil which are non-polar and insoluble in water, can be removed by soap through agitation that breaks up the grease molecule into small aggregates of grease molecules, embedded with non-polar tail of soap. These aggregates can be easily flushed away by water due to polar-ionic heads that stick to water molecules.

Even though soap are excellent cleansers, they still have disadvantage like they canˇt work out efficiently in hard water (water contain of divalent cations, Eg. Ca2+ and Mg2+). Anions of fatty acids in soap will form insoluble salts with these divalent cations and stick on the clothes and washing machine.

2CH3(CH2)16CO2-Na+ + Mg2 ---->

[CH3(CH2)16CO2-]2Mg2+ + 2Na+

(Soap) + ( Divalent Cations)

--->

(Insoluble salts)

HARD WATER

We use water everyday- for drinking, washing, cleaning and many other activities. Sometimes you may realize that while washing using soap, it doesn't lather up as easily as usual. Most of the time we tend to think that the fault lies with the soap or detergent, but actually the problem lies with the water used. This type of water is called 'hard water'.

It is more difficult for lather to form in hard water.

Hard water is water that has a comparatively higher mineral content that may consist of calcium cations, Ca2+, magnesium cations, Mg2+, sulphates, and bicarbonates. It is termed “hard” as opposed to soft water because of its mineral content.

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.

Salts used for water softening.

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.

Calcium buildup in a water pipe.

Calcification on a water tap.

MELAMINE TAINTED MILK

What passes through your mind when you see the word 'milk'? A tall, cold glass of creamy goodness. For many, milk plays a big part in everyday lives, whether they are children and adults.

A yummy glass of milk.

In November 2008, milk took the spotlight internationally in an unexpected way- tens of thousands of infants were reported to be sickened by the consumption of melamine-tainted milk formula. Most were hospitalized for severe kidney failure and kidney stones, 4 were reported dead. People from all over the world were horrified by the incidents and most of all by the culprit- melamine. So what exactly is melamine? How did it end up being added into milk products?

Disposal of contaminated baby milk formula.

Melamine is an organic base which is most commonly found in the form of insoluble white crystals. It is a trimer of cyanamide, with a 1,3,5-triazine skeleton.

Molecular structure of melamine.

Skeletal structure of melamine.

In the early production days, melamine is synthesized by first converting calcium cyanamide into dicyandiamide, and then heated to form melamine. Now, however, urea is used to commercially produce melamine with the following reaction:
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.

Melamine as a solid, white powder.

Melamine is combined with formaldehyde to produce melamine resin, which is widely used to make plastic products, adhesives, dishware, fabrics, countertops and dry-erase boards. Its high-nitrogen content enables it to have fire retardant properties, as it releases nitrogen gas when it comes into contact with flames. Sulfonated melamine formaldehyde (SMF) is a polymer used as cement admixture to make high-resistant concrete.

Melamine resin plate ware.

In the 1950s, melamine was introduced to the farming industry as a fertilizer, also because of its nitrogen content. However, it was considered economically impractical as it was more expensive to produce and the nitrogen takes far longer to be mineralized and absorbed by plants. Later on, it was used as ‘non-protein nitrogen’ in cattle feed as a substitute source for protein. In 1978, however, studies concluded that it ‘may not be acceptable ‘, due to its slow and incomplete hydrolysis.

In China, water had been added to raw milk so that the volume would be increased. As a result, the milk is diluted and thus has a low protein concentration. Companies which use the milk for further processing and production, such as manufacturing powdered infant formula and diet milk, would routinely check the raw milk’s protein level through a test that measures the nitrogen content. Milk with protein levels that are below par would be rejected. To cope with that, melamine was added to the raw milk increase the nitrogen content of the milk, and therefore its apparent protein content. Standard tests, such as the Kjeldahl test or Dumas test, estimate protein levels by measuring the nitrogen content, and the addition of melamine is done to mislead the tests so that the milk would be acceptable.
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.

One of the victims of melamine-contaminated milk.