Page 90 - Chemistry - XI

Chemical Reactions

I + H S → 2HI + S
2
2
I + 2Na S O → 2I + Na S O + 2Na +
–
2 2 2 3 2 4 6
Sodium tetrathionate
Result
The order in which samples of water are polluted is _______________ .

COMPETENCY BASED QUESTIONS

Multiple Choice Questions

Q1. Which of the following water is the safest? [BOD stands for biochemical oxygen demand]
(a) BOD < 5 (b) BOD > 17 (c) BOD = 100 (d) BOD = 50

Q2. What is the formula of Cadmium acetate?
(a) CdCOOCH (b) Cd(COOCH ) (c) Cd(COOCH ) (d) None of these
3 3 2 3 3
Q3. In the reaction, I + H S 2HI + S, which one is an oxidising agent?
2
2
(a) I (b) H S (c) S (d) I –
2–
2 2
Q4. In the reaction, I + 2Na S O Na S O + 2NaI, Na S O acts as
2 2 2 3 2 4 6 2 2 3
(a) a reducing agent (b) an oxidising agent (c) both (d) none of these

Answer Key
1. (a), 2. (b), 3. (a), 4. (a)

PROJECT - 2

Introduction

The purity of water obtained from diff erent sources is diff erent. The type of impurity present in water
depends upon its source. We need water for drinking, bathing, washing, agriculture and chemical analysis.
There are various methods of purifi cation depending upon the impurities present in it and obtained water of
specifi c purity for a specifi c purpose. According to WHO, 1.1 billion people lacks access to clean drinking
water. 88% of the 4 billion annual cases of diarrhoeal disease are attributed to unsafe drinking water.

Objective

To study the methods of purifi cation of water.

Steps for Purifi cation of Water
1. Sieving: This process is used to remove large suspended impurities like sticks, leaves, trash, fi sh, etc.
by passing water through a sieve with small holes. This method is needed for surface water and not for
underground water.
underground water.

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