Question

Shailesh lies in a bigh industrial city having a large number of chemical industries onits outskirts. This city has also a very heavy traffic density. There is a big lake in the middle of this city which has much less water left init but the lake has still a large number of fish in it. During the last one and a half months, there ha been to much rain in the city with the pH of rain water being about 5.5. One day people found that many fish in the lake ha died. No one knew the reason for the death of fish in the lake or how the death of remaining fish in the lake could be prevented. Shailesh, who is a student of class X could understand the reason for the death of fish in lake. He also suggested an immediate solutioin for the prevention of death of more fish in the lake water.
(a) What conclusion do you draw the fact that the rain water has a pH of about 5.5? What name is given to such a rain?
(b) What makes the pH of rain water to be about 5.5?
(c) What happens to lake water when too much rain water haivng pH of 5.5 collects in it?
(d) Why have the fish died after the heavy rains?
(e) Why suggestion do you think has been made by Shailesh to prevent the death of more fish in the lake? Why
(f) What values are displayed by Shailesh in this episode?

Answer 1

(a) The rain water having a pH of about 5.5 is acidic in nature. Such a rain is called acid rain.
(b) The chemical inductrias and heavy traffic (vehicles) in this city emit many harmful gases into the air and pollute it. The acidic gases (such as sulphur dioxide and nitrogen oxides) present in polluted air dissolve in rain water to produce acids. The presence of the acids lowers the pH of rain water to about 5.5 (making it quite acidic in nature).
(c) Too much acid rain can lower the pH of lake water appreciably and make it highly acidic.
(d) The high acidity of lake water caused by too much acid rains has caused the death of fish in the lake.
(e) Shailesh might have suggeted adding calcium carbonate to the lake water. This is because calcium carbonate neutralises the excess cid present in lake water (which comes from acid rain), reducing the acidity of lake water. This reduction in the acidity of lake water can prevent the death of more fish in the lake.
(f) The various values displayed by Shailesh in this episode are (i) Awareness (or knowledge) of the occurrence of acid rain and its harmful effects on aquatic animals such as fish (ii) Understanding of neturalisation reaction involving acidic and basic susbtances and (iii) Concern to save the life of remaining fish in the lake.