Properties, uses tests of ethanol or ethyl alcohol
By Anup Pokhrel
Ethanol or ethyl alcohol.
It is the most important and the earliest representative of the class and is popularly referred to as simply alcohol. It is the exhilarating principle of all wines and is thus named as spirits of wines. technically, it is known as grain alcohol since it often manufactured from starchy grains.
Ethyl alcohol is produced in plants and animals by the fermentation of the carbohydrate. Thus it can be present in tissues, blood and urine of diabetic persons. It is also present in the human brain to the extent of 0.025 percent.
It can be prepared by any of the general methods of preparations. On the commercial scale, it is manufactured by fermentation of carbohydrate or by hydration of alkenes.
Ethyl alcohol is a colourless mobile liquid with characteristic pleasant odour and burning taste. It boils at 78.50C,freezes at -1140C and has specific gravity 0.789 at 200C. It mixes with water in all proportions with an evolution of heat and a concentration in volume. The maximum contraction of 3.7 percent takes place when 52 volumes of alcohol are mixed with 48 volumes of water. It is an excellent solvent for fats, resins and much more organic substance.
It also dissolves inorganic substances like caustic soda, caustic potash, sulphur, phosphorous etc. When taken orally in small dosages,alcohol is the good stimulant. It is directly absorbed into the blood stream and produces heat owing to oxidation and hence, it is used as a medicine for contraction cold. If swallowed in the large amount,it acts as a strong poison. It gives all the general reactions of alcohol.
Ethanol is used for following purposes.
- as a fuel for lamps and stoves. For the sake of conversion in transportation, it is converted into the solid state (solid alcohol) by dispersion in saturated calcium acetate and a little steric acid.
- as a substituent of petrol in internal combustion engines.
- as a solvent for drugs, tinctures, oils, perfumes, inks dyes, varnishes etc.
- as beverages.
- as an antifreeze for automobile radiators.
- as a preservative for biological specimens.
- as a low freezing and mobile fluid in scientific apparatus such as thermometer and spirit levels.
- as a raw material for a large number of organic compounds including ethene, ether, acetic acid, iodoform, chloroform , chloral etc.
Following tests are used for identifying ethanol.
1. Iodoform tests.
When ethanol is warmed with iodine and potassium or sodium hydroxide solution, yellow crystals of iodine are formed. This test can be employed for distinguished ethyl alcohol from methyl alcohol as the later fails to respond to it.
2. Esterification test.
Ethanol on warming with anhydrous sodium acetate and concentrated H2SO4 from ethyl acetate which is easily detected by its fruity smell.
some modified forms of ethyl alcohol.
a. Industrial alcohol. The alcohol obtained from the fractional distillation of the fermented liquor contains about 95% of ethanol and is called industrial alcohol. It is also known as rectified spirit and is used for industrial purposes.
b. Absolute alcohol.
Rectified spirit obtained from the distillation of the fermentation liquor wash contains about 95% of ethanol . Since a mixture of 95.6% alcohol with water boils at the lower temperature (78.10C) than the boiling point of pure alcohol (78.5%C), it is impossible to get an alcohol of higher concentration by fractional distillation of rectified spirit . Absolute alcohol (100% pure alcohol) can be obtained by digestion of rectified spirit over quick lime for several days and then distilled. The first and the last running are rejected, and the main portion of the distilled is 100% or absolute alcohol.
A modern process is the azeotropic distillation of rectified spirit with benzene . When distillation is carried out after the abduction of a certain amount of benzenes, at the first ternary mixture of water, ethanol and benzene come over at 650C till all the water is removed. Then the boiling point rises and remaining benzene comes over as the binary mixture with ethanol at 600C. Finally, absolute alcohol distills at 78.50C.
c. Denature of alcohol.
The manufacture and sale of ethyl alcohol are government controlled. Heavy excise duty is levied on the sale of alcoholic beverages.For industrial purpose alcohol is duty-free. Therefore, the industrial alcohol is denatured (made until for drinking purpose), by the addition of poisonous substance like methanol, acetone or pyridine. A common practice is to add about 4 % impure methanol together with traces of pyridine and some colouring matter. The product is often sold in the maker under the name methylated spirit. Methylated spirit is extensively used for the preparation of varnishes and tinctures for external use.
d. Power alcohol.
In non-poisonous countries, alcohol mixed with petrol and benzene is now used as motor fuel. Alcohol thus used for the generation of power is popularly known as power alcohol. Rectified spirit alone does not mix with petrol, hence the third ingredient such as ether or benzene is needed. In countries like Nepal with no petroleum resources, the use of power alcohol is a dire necessity. we can make large quantities of cheap alcohol from molasses which could be used to prepare power alcohol.
e. Alcoholic beverages.
When alcohol is taken internally in small quantities, it stimulates the human system without any apparent injurious effect. However, its continuous use leads to immoderation and induces other vices. Already the governments of the various countries have schemes of prohibition in hand. Anyhow, the fact remains that alcohol is consumed in large quantities as alcoholic liquor or beverages.
Alcoholic beverages are of two types.
1. Undistilled beverages.
These are produced simply by the fermentation process from fruit-juice or grains. The beverages prepared from grape juice or other juices are called wines. Wines containing 18-20 % alcohol and produced by natural fermentation are called natural wines. Weak natural; wines are made strongly by adding pure alcohol from outside and are named as fortified wines.
2. Distilled beverages.
If the fermented are distilled, most of the alcohol along with other volatile produce viz, flavours ,essential oils,ester and higher alcohol pass over as distillate. The distilled liquor have a high alcohol content which may go up to 505 or even more.