Question

Obtain a sample of rainwater. Add to it a few drops of universal indicator. Measure its pH. Describe the nature of the sample of rainwater and explain the effect if it has on the living world.

Answer 1

Ans7.This is an activity based question in which you are supposed to collect rainwater from different places and compare there results on the basis of following parameters :
a) pH of water
b)Action of water on blue litmus paper
c)Action of water on red litmus paper
d)Effect of indicator like phenolphthalein and methyl orange
Conclusion :
If we take samples of rain water from different places, we observe the following results :

• pH of water is in between 1-6
• Blue litmus paper turns red
• No change in colour of red litmus paper
• No change in colour of rain water on adding phenolphthalein
• rain water turns red in colour on adding methyl orange

The above observations show that rainwater is acidic in nature. For further assurance, we cancompare blue litmus paper dipped in different samples of rainwater with pH scale.
If rain water is acidic, then its pH must be in the range of 0-6.
The strength of ac acid depends on its pH value i.e. lower the value of pH, higher will be the strength of an acid and vice-versa.