Question 9 - Case Based Questions (MCQ) - Chapter 2 Class 10 - Acids, Bases and Salts

A dry pellet of a common base B when kept in open absorbs moisture and turns sticky. The compound is also a by-product of the chlor-alkali process.  

(a) Identify B:  

(i) Sodium chloride 

(ii) Sodium hydroxide  

(iii) Carbon dioxide 

(iv) Sodium carbonate  

Ans. 

Given that

Common base Base B , when kept in open, absorbs moisture

Now,

• Chlor-Alkali process is a method for the industrial production of sodium hydroxide and chlorine by the electrolysis of sodium chloride solution.  
• Since B is a base, it cannot be sodium chloride because it is a salt.
  Therefore, B is sodium hydroxide (NaOH)
  
  So, the correct option is (ii) Sodium hydroxide

(b) What type of reaction occurs when B is treated  with an acidic oxide?  

(i) Neutralisation  

(ii) Double decomposition  

(iii) Combination  

(iv) Displacement  

Ans.

Here, 

• Neutralisation reaction : In this, acid and base react with each other to form salt and water.
• Double decomposition reaction: it is a reaction between two compounds in which each are interchanged to form two new compounds i.e. AB+CD→AC+BD

• Displacement Reaction: Reaction in which more reactive element takes the place of less reactive element.
• Combination Reaction: When two or more substances react to form a single product, it is known as combination reaction i.e. A+B→C+D
  
  Since B is Sodium Hydroxide i.e a base , when we react it with an acidic oxide , neutralization reaction will take place.
  
  So, the correct answer is (i) 

(c) What is the raw material used in chloro-alkali?  

(i) aqueous solution of sodium chloride  

(ii) sodium chloride in dry form  

(iii) sodium hydroxide  

(iv) sodium carbonate  

Ans.

• The raw material used in the chlor-alkali process is aqueous solution of sodium chloride , also known as brine .
• We use aqueous NaCl and not dry NaCl because in presence of water, NaCl dissociates to produce Na ⁺ and Cl ^- ions which conduct electricity.
  
  So, the correct answer is (i) 

(d) When aqueous sodium carbonate (Na 2 CO 3 ) reacts  with HCl (aq), it gives  

(i) NaOH, H ₂ and CO ₂   

(ii) NaCl, H ₂ O and CO ₂   

(iii) NaHCO ₃ , H ₂ and CO ₂   

(iv) NaHCO ₃ , H ₂ O and CO ₂

Ans. 

Sodium carbonate is basic in nature. So, when it reacts with HCl (acid), a neutralisation reaction takes place and salt, water and CO ₂ is produced.

The reaction is as follows: 

Na ₂ CO ₃ (aq) + 2HCl(aq) → 2NaCl + H ₂ O + CO ₂