- No.11. How detergents make the water unfit for aquatic life?
Answer. The phosphate salts present in detergents, causes rapid growth of algae in water bodies, which floats over the surface of water. These plants ultimately die and decay. Decaying plants being biodegradable consume O2 present in water. Thus, depletion of O2 results in death of aquatic life. In this way detergents make the water unfit for aquatic life.
- No.12. Why pesticides are used?
Answer. Pesticides are used either directly to kill or control the growth of pests. Pests may be weeds herbs, insects, fungi, viruses, etc. They all damage crops and transmit diseases both to human beings and animals.
- No.13. What are the reasons of waterborne diseases?
Answer. Lack of proper sanitation facilities is the main cause of rapidly spreading of waterborne diseases. Water pollution may be due to toxins or microorganisms. Toxins are arsenic, mercury, lead and many organic chemicals. Microorganisms such as viruses, bacteria, protozoa and worms are the reasons of water borne diseases.
- No.14. How waterborne diseases can be prevented?
Answer. Waterborne diseases can be prevented by taking the following measures:
(i) Provision of safe water: Drinking water must be properly treated and purified.
(ii) Disposal of sewage: There must be adequate sanitary disposal of sewage. Any type of waste must not be thrown or discharged directly in water supplies or
(iii) Control of toxic chemicals: Chemical contamination can cause acute illness, but often toxic contaminants are slow poisons and carcinogens. There must be a strict- control over the use of pesticides and other chemicals.
- No.1. How polarity of water molecule plays its role to dissolve the substances?
Answer. Water molecule has a polar structure, i.e., one end of the molecule is partially positive while the other end is partially negative because of electronegativity difference between oxygen and hydrogen atoms. All other polar substances are soluble in water, because the positive end of the substance is attracted by the negative end (O–) of the water and negative end of the substance is attracted by the positive end (H+) of the water. The electrostatic forces attraction among the ions is overcome by the ion-dipole forces of attraction between ion and water molecules. In this way positive and negative ions of the compounds are pulled apart as shown in figure. Ultimately, these oppositely charged ions are surrounded by water molecules, thus separated and kept in solution. For example, most of the salts like NaCl, KC1, Na2SO4, etc., are soluble in water.