The Uses of Various Chemical Substances Quiz

Answer: iodine (I)

A tincture of iodine contains iodine in ethyl alcohol (the solvent), mixed with some potassium iodide (KI). Methyl alcohol is not used as it is poisonous. This solution is reddish brown in colour. When applied on cuts and wounds, iodine, being an antiseptic, helps prevent infections. Iodine can also be used to get relief from pain when it is mixed with petroleum jelly to make a paste.

Answer: carbon dioxide (CO2)

Water, though the most common fire extinguisher, cannot be used to put out electrical fires, as common water, which contains dissolved salts in it, is a good conductor of electricity, and therefore would allow the electricity to flow. This could harm the electrical equipment.

However, carbon dioxide does not do so. It does not harm the electrical equipment. Although gaseous normally, carbon dioxide can be stored as a liquid under immense pressure. When released, it expands enormously and covers the burning substance like a blanket, cutting off the supply of oxygen, which stops the combustion. Also, when released, it cools down a lot. Thus, apart from acting as a blanket, it also lowers the temperature of the burning substance. If its temperature falls below the ignition temperature (the minimum temperature required to burn), it stops burning.

Answer: alloys of mercury, along with silver, tin and copper

Previously, alloys of gold or silver(mixed with some other substances to make them tougher) were used to fill the tooth cavities, but they are so expensive that dental amalgams became more popular. However, they are not a perfect alternative to our teeth, so we should not give up our habit of brushing our teeth thinking that the dental amalgams will fill the cavities! The popularity of amalgams has decreased due to concerns about the toxicity of mercury.

Answer: LPG

LPG stands for Liquefied Petroleum Gas. Petroleum gas is a gaseous fuel obtained from the fractional distillation of petroleum. Petroleum gas can be however stored as a liquid (in LPG) under immense pressure. LPG is preferred to solid fuels such as coal and liquid fuels such as petrol as LPG is a gaseous fuel and therefore burns more completely. It also produces less solid residue such as soot and harmful poisonous substances such as carbon monoxide (CO). LPG also has a higher calorific value. Its primary constituent is butane. Butane combines with the oxygen in the air to form carbon dioxide and water vapour. The chemical reaction is:-

2C4H10 + 13O2 = 8CO2 + 10H2O

Butane is a compound of the alkane group. Hydrogen, although non-polluting, is not used as it is highly reactive and is unsafe to carry, handle and use.

Answer: aluminium (Al)

Silver is the best conductor of electricity but it is not used to make these wires as it is very expensive. Copper is the next best conductor of electricity, followed by aluminium. Domestic wires are covered by a layer of electrical insulation, such as bakelite, for safety. All metals (except tungsten) are good conductors of electricity as they have free electrons in their valence shell. Sodium is not used as it is a soft and highly reactive metal. Aluminium is ductile, i.e. it can be drawn into wires, and is thus used for electrical transmission.

Answer: zinc (Zn)

Iron reacts with the water vapour and oxygen in the air when left exposed in moist air and forms a layer of hydrated ferric oxide or rust (Fe2O3.xH20 - the number of water molecules varies). The rust formed slowly eats away the metal. Galvanization is done to prevent this.

The iron article is placed in molten zinc in this process, then it is allowed to cool. The molten zinc solidifies to form a firm coating on the iron article. The layer of zinc acts as a protective layer and prevents rusting. Although electroplating is a better method of protection, it is more expensive.

Answer: calcium sulphate

Calcium sulphate is used as plaster of Paris as 2CaSO4.H2O. Plaster of Paris is used to support broken bones during the healing process. When a broken limb is set in a cast made of a paste of plaster of Paris in water, movement of the bone is restricted, which helps the bone to heal. Calcium sulphate is also used as gypsum (CaSO4.2H2O) in the cement industry. Calcium sulphate is a salt.

Answer: chlorine (Cl)

Chlorination purifies the water. Chlorine gas forms a mixture of hydrochloric acid (HCl) and hypochlorous acid (HOCl) when passed through water. Hypochlorous acid is, however, quite unstable. Thus the hypochlorous acid breaks down into oxygen and hydrochloric acid when the resulting acidic mixture is placed in sunlight or heated. The hydrochloric acid formed kills the germs present in water. However this has to be done cautiously as an excess of hydrochloric acid could be harmful for those swimming in the swimming pool.

Cl2 + H2O = HCl + HOCl

or 2Cl2 + 2H2O = 2HCl + 2HOCl
or 2Cl2 + 2H2O = 2HCl + 2HCl + O2
Result:-
2Cl2 + 2H2O= 4HCl + O2

Answer: tartaric acid

The molecular formula of tartaric acid is HO2CCH(OH)CH(OH)CO2H. Its basic formula is simply C4H6O6. Tartaric acid is used as a souring agent and can also be found in baking powder. Tartaric acid is an organic acid and is less corrosive than mineral acids. Oxalic acid is found in tomatoes. Ascorbic acid is Vitamin C. Citric acid is found in citrus fruits such as lemon and orange.

Answer: nitric acid and hydrochloric acid

Aqua regia is the most powerful acidic mixture. The upper layer of gold articles becomes dull when exposed to moist air for a long time, so gold articles can be placed in aqua regia solution in order to clean them. Then the acid reacts with the impurities present.

The upper layer of gold gets washed away due to this and there is a loss of mass, exposing the inner layer. The gold article appears polished as the shine of the inner layer of gold is still intact. Items should not be left in the solution too long, or they will dissolve completely.