Question

Write answers to the following

a. Write about artificial food colours, the substances used in them and their harmful effects.

b. What is meant by water of crystallization? Give examples of salts with water of crystallization, and their uses.

c. Write briefly about the three methods of electrolysis of sodium chloride.

Answer 1

a. Food colours are often mixed with most of the available foodstuff in the market, such as sweets, soft drinks, cakes, ice creams, meat, spices etc. These food colours are present in the form of powders, gels and pastes. They are used in domestic as well as commercial products. These food colours can be natural as well as artificial in nature. Tartrazene and sunset yellow are extensively used artificial food colours. While natural food colours are harmless and can be consumed without worry, artificial food colours, on the other hand, do have some adverse effects. Consuming these on a regular basis is harmful for us as they contain small quantities of lead and mercury. Excessive consumption of foods with added artificial colours can cause diseases like ADHA (Attention Deficit Hyperactivity Disorder) in children.

b. Water of crystaliization is the amount of water molecules which are present in one formula unit of salt. We can also say that the water molecules which form part of a structure of a crystal are called water of crystaliization. They give the crystals their shape and crystal.

Example:
CuSO₄.5H₂O- Copper sulphate- it is used as an antiseptic and as an antifungal agent for topical use.
CaSO₄.2H₂O- Calcium sulphate- it is used in the manufacture of Plaster of Paris and also used in tofu as a coagulant.

c. Electrolysis of sodium chloride solution with inert electrodes can be done by chemical electrolysis, producing different sets of products by providing different experimental conditions .

• Solid sodium chloride melts at just over 800^oC, and electrolysis of molten sodium chloride yields sodium metal at the cathode and chlorine gas at the anode.
• Concentrated aqueous sodium chloride solution with a mercury cathode produces a solution of sodium metal in mercury ("sodium amalgam") and chlorine at the anode.
• Dilute aqueous sodium chloride solution produces hydrogen at the cathode and oxygen at the anode.
• Concentrated aqueous sodium chloride solution produces hydrogen at the cathode and chlorine at the anode.

Sodium metal and chlorine gas can be obtained with the electrolysis of molten sodium chloride.Electrolysis of aqueous sodium chloride yields hydrogen and chlorine, with aqueous sodium hydroxide remaining in solution.The reason for the difference is that the reduction of Na⁺ (E° = –2.7 v) is energetically more difficult than the reduction of water (–1.23 v).