Q.

Read the passage carefully and answer the following questions from (i) to (v):

 

The use of a universal indicator, which is a mixture of several indicators, can be helpful in judging how strong a given acid or base is. The universal indicator shows different colours at different concentrations of hydrogen ions in a solution. Here is a scale for measuring hydrogen ion concentration in a solution, called pH scale. The ‘p’ in pH stands for potenz in German, meaning power. On the pH scale, we can measure pH from 0 (very acidic) to 14 (very alkaline).

pH should be thought of simply as a number which indicates the acidic or basic nature of a solution. Higher the hydronium ion concentration, lower is the pH value.

The pH of a neutral solution is 7. Values less than 7 on the pH scale represent an acidic solution. As the pH value increases from 7 to 14, it represents an increase in OH- ion concentration in the solution, that is, increase in the strength of alkali.

 

 

(i) When hydrogen chloride gas is prepared on a humid day, the gas is usually passed through the guard tube containing calcium chloride. The role of calcium chloride taken in the guard tube is to:

1 absorb the evolved gas  
2 moisten the gas  
3 absorb moisture from the gas  
4 absorb Cl-ions from the evolved gas  

Ans.

(3)