Question

A non-metal which reacts with concentrated sulphuric acid to form two gases which turn lime water milky is ______.

• A. Sulphur
• B. Carbon
• C. Oxygen
• D. Nitrogen

Hint:

While both gases turn lime water milky, SO_2 can be distinguished because it has a pungent smell of burning sulphur and turns acidified potassium dichromate paper green!

Answer 1

The Correct Option is B

Step 1: Understanding the Chemical Reaction: 
Concentrated sulphuric acid (H_2SO_4) acts as a powerful oxidizing agent. When it reacts with elemental carbon, it oxidizes the carbon to carbon dioxide while being reduced to sulphur dioxide. 

Step 2: Identifying the Product Gases: 
The balanced chemical equation for the reaction is: [ C + 2H_2SO_4 (textconc.) CO_2 + 2SO_2 + 2H_2O ] The two gaseous products are Carbon dioxide (CO_2) and Sulphur dioxide (SO_2). 

Step 3: Lime Water Test: 
Both CO_2 and SO_2 have the property of reacting with lime water [calcium hydroxide, Ca(OH)_2] to form a white precipitate (CaCO_3 and CaSO_3 respectively), which makes the solution appear milky. 

Step 4: Final Answer: 
Carbon is the unique non-metal in this list that produces both of these gases simultaneously upon reaction with concentrated acid.