Question 6 - Case Based Questions (MCQ) - Chapter 1 Class 10 - Chemical Reactions and Equations

P, Q and R are 3 elements which undergo chemical  reactions according to the following equations  Answer any four question from I to V:  

(i) P ₂ O ₃ + 2Q → Q ₂ O ₃ + 2P  

(ii) 3RSO ₄ + 2Q → Q ₂ (SO ₄ ) ₃ + 3R  

(iii) 3RO + 2P → P ₂ O ₃ + 3R  

(a) The most reactive and the least reactive elements  are:   

(i) Q and P 

(ii) Q and R  

(iii) R and Q 

(iv) R and P  

Answer

• In the first reaction , Q is able to replace P from its salt i.e. P ₂ O ₃ , Q is more reactive than P.
• In the second reaction, Q is also able to replace R from its salt solution i.e. RSO 4 , Q is more reactive than R .
• In the third reaction, P is able to replace r from its oxide, so, P is more reactive than R

Therefore, the r eactivity order is: Q > P > R ( Q being the most reactive and R being the least)

Thus,

• Most Reactive is Q
• Least Reactive is R

So, the correct answer is  (ii) 

(b) The type of reaction is:   

(i) Displacement reaction  

(ii) Combination reaction  

(iii) Neutralisation reaction  

(iv) Substitution reaction  

Ans. 

Let’s look at all the options

• 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.
• Neutralisation reaction : A reaction in which acid and base react to form salt and water
• Substitution Reaction: In this reaction, one functional group in a chemical compound is replaced by another.

Since in the above mentioned reactions, the more reactive elements (Q, P) are replacing the less reactive element (R), this is a displacement reaction . 

So, the correct answer is (i) Displacement reaction

(c) 3RSO ₄ + 2Q → Q ₂ (SO ₄ ) ₃ + 3R  The given reaction shows: 

(i) Q is more reactive than R  

(ii) Q is less reactive than R  

(iii) Q and R are equally reactive  

(iv) none of the above  

Ans. 

Since in this reaction, Q is able to replace R from its salt RSO ₄ , 

Therefore, Q is more reactive than R.

So, the correct answer is (i)

(d) Choose the correct statement: 

(i) Zinc and lead are more reactive elements than  copper.  

(ii) Zinc and lead are less reactive elements than  copper.  

(iii) Zinc and copper are more reactive elements  than lead. 

(iv) Copper and lead are more reactive elements  than zinc.  

Ans. 

According to the reactivity series, 

Zinc and lead are more reactive than copper because they both are able to replace copper from its salt solution.

So, the correct answer is (i) 

(e) Na ₂ SO ₄ (aq) + BaCl ₂ (aq) → BaSO ₄ (s) + 2NaCl(aq)  

The above reaction is an example of: 

(i) Double displacement reaction.  

(ii) Displacement reaction. 

(iii) Can be both.  

(iv) None of the above.  

Ans. 

Since in this reaction the two reacting compounds are switching their positive and negative ions, 

it is a double displacement reaction. 

So, the correct answer is (i)