Question

(a) What is detergent?
(b) Explain the causes of Ozone depletion.
(c) Draw a labelled diagram of 'Khadin water harvesting system' and write any two measures of water conservation.

Answer 1

Figure 1: Khadin water harvesting system.

a) Detergent is a surfactant or a clearing agent which helps to remove dirt/ grease from porous surfaces, like clothes etc. The working of a detergent depends upon its amphipathic nature. Detergents contain two components; a hydrophilic head and a hydrophobic tail.

When the detergents are mixed in water, they aggregate forming special structures called as micelles. The formation of micelles is dependant on the concentration of the detergent in the aqueous media (water), or critical micellar concentration (CMC). CMC is defined as the concentration at which micelle begin to form.

At high concentrations (of the detergent), the polar hydrophilic region of each molecule is oriented towards the polar solute i.e. water, whereas the hydrophobic moities aggregate together; the whole structure thus formed is called as 'micelle'.

The cleaning action of detergents is due to the binding of these micelles to the cloth stains, thereby decreasing the surface tension and increasing miscibility of the surface (stain).

Depending upon the form of the hydrophilic group, detergents can be classified as follows:

1. Anionic detergents,

2. Cationic detergents,

3. Non-ionic detergents, and

4. Zwitterionic detergents.

Detergents have a high applicability value. They are used to wash clothes, vary the solubility of formulations, proteins etc., in stabilization, crystallization, denaturation of proteins and changing the surface properties of liquids.

b) Ozone is a colourless gas made from three oxygen molecules. This gas is found in the earth's stratosphere i.e. uppemost atmosphere. The ozone layer absorbs the harmful ultraviolet rays and thus protects these rays from reaching the earth's surface. Ozone layer depletion is one of the most major environmental concerns. The depletion of the ozone layer leads to serious issues like global warming, melting of polar ice caps, health hazards including skin cancers etc.

The main causes of ozone depletion are as follows:

1. Chlorofluorocarbons (CFCs)

These are the group of compounds containing halogens like chlorine and fluorine . Such substances are found in the emissions of vehicles, by-products of industrial processes, aerosols and refrigerants. These substances when released in the atmosphere, travel above upto the stratosphere, wherein they undergo breakdown followed by the release of chlorine gas which further reactswith ozone. This reaction causes depletion of the ozone layer. CFCs amount to 80% of the total ozone layer depletion factors. The CFCs are used in refrigeration, air conditioning and plastic foam manufacturing.

2. Hydrochlorofluorocarbons (HCFCs)

The HCFC compounds are formed by H, Cl, F and C atoms. They are the substitutes for CFCs. They cause less depletion of ozone layer as compared to the CFCs.

3. Halons

These are the compounds formed by Br, F and C. Bromine is a more potent ozone depleting agent as compared to chlorine. Halons are used in the manufacturing of fire extinguishers and its use is also banned in some countries which are affected by ozone depletions.

4. Methyl bromide

Contains bromine and is used as a pesticide, depletes the ozone layer.

5. Carbon tetrachloride (CCl4)

CCl4 is an industrial agent used as a solvent found to have ozone depleting and carcinogenic effects.

6. Air pollution due to vehicular emissions, low temperature and the presence of halogens in the atmosphere are the other causes of ozone depletion.

c) The Khadin water harvesting system (see figure 1) was first designed by the Paliwal brahmins of Jaisalmer, Rajasthan in the 15th century. Khadin, commonly known as dhora is an ingenious construction designed to harvest surface runoff water of agriculture.Khadin consists of earthen embankments built across the lower hill slopes lying below gravelly uplands. Excess water is drained off by spillways and sluises. This system is based on the principle of watre harvesting for farmland and its use for crop production.

Two measures for water conservation:

1. Fix all the leaky pipes and connections.

2. Close taps tightly after use.