Question 7 - Case Based Questions (MCQ) - Chapter 2 Class 10 - Acids, Bases and Salts

Suhana wanted her house to be white washed. She  bought 10 kg of quicklime from the market and  dissolved it in 30 L of water. On adding lime to  water, she observed that the water started boiling  even when it was not being heated.  

(a) Name the product when water is added to  quicklime.   

(i) Calcium oxide 

(ii) Calcium hydroxide  

(iii) Calcium dioxide 

(iv) Calcium carbonate  

Ans.

When water is added to quick lime, slaked lime i.e. Calcium hydroxide is formed.

The reaction is as follows:

So, the correct answer is (ii) Calcium hydroxide

(b) The common name for quick lime is:  

(i) Calcium hydroxide 

(ii) Calcium oxide  

(iii) Calcium dioxide 

(iv) Calcium carbonate  

Ans. 

The common name for quick lime is Calcium oxide  

So, the correct answer is (ii)

(c) The correct formula for calcium hydroxide is:  

(i) Ca(OH) 

(ii) Ca(OH ₂ )  

(iii) Ca(OH) ₂  

(iv) Ca ₂ OH ₂   

Ans. 

The correct formula for calcium hydroxide is Ca(OH) 2

So, the correct answer is (iii) 

(d) Which of the following statements is correct about  the above reaction based on your observations?  

(i) It is an endothermic reaction.  

(ii) It is an exothermic reaction  

(iii) The pH of the resulting solution will be more  than seven.  

(iv) The pH of the resulting solution will be less  than seven.  

1. I and II 
2. II and III  
3. I and IV 
4. III and IV  

Ans. 

Here, 

• Exo means out and thermic means heat. Exothermic reactions are the ones in which heat is released .
• Endo means in and thermic means heat. Endothermic reactions are the ones in which heat is absorbed .

Since 

• Heat is given out when quick lime reacts with water and,
• Ca(OH) ₂ is formed which is basic in nature, 
• The reaction is exothermic and pH of resulting solution will be more than 7

So, the correct option is (II)