Question 3 - Case Based Questions (MCQ) - Chapter 3 Class 10 - Metals and Non-Metals

Read the following passage and answer any four  questions from (a) to (e).  Sohan went door to door posing as a goldsmith.  He promised to bring back the glitter of old and dull gold ornaments. An unsuspecting lady gave a set of gold bangles to him which he dipped in a  particular solution. The bangles sparkled like new  but their weight was reduced drastically. The lady was sad but after a futile argument, the man beat a hasty retreat.  

(a) Which of the following is used for dissolution of  gold?  

(i) Hydrochloric acid  

(ii) Sulphuric acid  

(iii) Nitric acid  

(iv) Aqua regia  

Answer

Aqua Regia is a mixture of concentrated HNO3 and concentrated HCl. 

• It is used by jewellers and blacksmiths for dissolution of gold .
• It removes the top corroded layer of gold and returns its shine.

So, the correct answer is (iv)

(b) The composition of aqua-regia is  

(i) Dil. HCl: Conc. HNO ₃ 3: 1  

(ii) Conc. HCl: Dil. HNO ₃ 3: 1  

(iii) Conc. HCl: Conc. HNO ₃ 3: 1  

(iv) Dil. HCl: Dil. HNO ₃ 3: 1  

Answer

(iii) Aqua regia is a mixture of nitric acid  and hydrochloric acid , that is 3 parts conc. HCl and  one part conc. HNO3 (3: 1).     

So, the correct answer is (ii)

(c) Which of the following is incorrect?  

(i) Aqua regia is a strong oxidising agent.  

(ii) Aqua regia is a strong reducing agent.  

(iii) Aqua regia dissolves gold in it.  

(iv) Aqua regia is a mixture of hydrochloric acid  and nitric acid.  

Answer

• Aqua regia is a strong oxidising agent  
• It is not a strong reducing agent.
• It is used to dissolve gold because of its oxidising properties.. 
• It is a mixture of HCl and HNO ₃ .

So, the correct answer is (ii)  

(d) Aqua regia dissolves:  

(i) Gold and platinum  

(ii) Gold and silver  

(iii) Platinum and silver  

(iv) Only gold 

Answer 

Aqua regia is a strong oxidising agent . 

It is used to dissolve many unreactive metals like gold and platinum. 

It does not dissolve silver because silver forms a protective layer of oxides around.

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So, the correct answer is (i)

(e) Examples of Noble metals are:  

(i) Gold 

(ii) Silver  

(iii) Platinum 

(iv) All of the above  

Ans. 

• Noble metals are metals that are very less reactive, do not corrode and are not easily attacked by acids.
• Gold, silver and platinum are all very less reactive , and do not corrode . They do not react with mild acids. 

So, the correct answer is (iv) all of the above