Q30 of 805 Page 194

Although coal and petroleum are produced by degradatioin of bio- mass, yet we need to conserve them. Why?

Production of coal and petroleum by degradation of biomass is a natural process. Although it is natural, it takes several million years to be completed. If these fossil fuels are used in excess, then it will lead to their unavailability. Hence, future generations will not be able to use these fuels. Hence, sustainable use of fossil fuels is necessary.


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28

A person needs a lens of power –4.5 D for correction of her vision.

(a) What kind of defect in vision is she suffering from?


(b) What is the focal length of the corrective lens?


(c) What is the nature of the corrective lens?

 29

In a village in Karnataka, people started cultivating crops all around a lake which was always filled with water. They added fertilisers to their field in order to enhance the yield. Soon they discovered that the waterbody was completely covered with green floating plants and fish in the lake started dying in large numbers. Analyse the situation and give reasons for excessive growth of plants and death of fishes in the lake.

 31

In the following schematic diagram for the preparation of hydrogen gas as shown in Figure, what would happen if following changes are made?


(a) In place of Zn granules , same amount of zinc dust is taken in the test tube


(b) Instead of dilute sulphuric acid, dilute hydrochloric acid is taken


(c) In place of Zn, Cu turnings are taken


(d) Sodium hydroxide is taken in place of sulphuric acid and tube is heated


OR


A metal carbonate X on reacting with an acid gives a gas which when passed through a solution Y gives the carbonate back. On the other hand, a gas G that is obtained at anode during electrolysis of brine is passed on dry Y, it gives a compound Z, used for disinfecting drinking water. Identity X, Y, G and Z. Also, write the chemical reactions involved.

 32

When ethanoic acid reacts with sodium hydrogencarbonate, a salt X is formed and a gas Y is evolved.

(a) Identify X and Y. Write chemical equation of reaction involved.


(b) Describe an activity and draw the diagram of the apparatus to prove that the evolved gas is the one which you have named.


OR


Look at Figure and answer the following questions.



(a) What change would you observe in tube B containing calcium hydroxide solution


(b) Write the reaction involved in test tubes A and B respectively


(c) If ethanol is given instead of acetic acid, would you expect the same change?


(d) How can a solution of lime water be prepared in the laboratory?