Question

Assertion:
Concentrate and not dilute ${{H}_{2}}S{{O}_{4}}$-behaves as a dehydrating agent.
Reason:
Concentrated sulphuric acid behaves as a strong dehydrating agent as the hydration reaction is highly exothermic. It has a strong affinity for water removing water molecules from other compounds.
A) Both assertion and reason are correct and reason is the correct explanation for assertion.
B) Both assertion and reason are correct but reason is not the correct explanation for assertion.
C) Assertion is correct but reason is incorrect
D) Both assertion and reason are incorrect.

Answer 1

Hint: Dehydrating agent refers to a chemical compound which on adding to the reaction mixture removes the water molecules from the mixture.
- A diluted form of acid means that the concentrated acid or the pure strong form of an acid is diluted with water.

Complete Solution :
So in the question two statements, an assertion statement and a reason statement are given and we have to say, whether the statements are correct and the reason statement explains and supports the assertion statement.
- We know that sulphuric acid (conc. ${{H}_{2}}S{{O}_{4}}$) is one of the strongest acids known for us.
One of the practical evidence that puts forward that it is a strong acid is that when the concentrated acid unknowingly comes in contact with our skin ,we get a burning sensation and it burns our skin in that area. That is why we are always said to be cautious when handling the concentrated sulphuric acid as there is a high chance of getting the skin burnt badly.
- The burning sensation is due to the dehydration of our cells present in the skin of that area.Sulphuric acid dries up our cell and that area of skin gets burnt.
- Sulphuric acid is one of the good dehydrating agents known,it absorbs the moisture from the surrounding atmosphere.
Another one best example to show that conc. ${{H}_{2}}S{{O}_{4}}$ is a strong dehydrating agent that,when glucose is treated with con. ${{H}_{2}}S{{O}_{4}}$, we obtain C.
${{C}_{6}}{{H}_{12}}{{O}_{6}}\xrightarrow{{{H}_{2}}S{{O}_{4}}}6C+6{{H}_{2}}O$

- When conc.${{H}_{2}}S{{O}_{4}}$ is added to glucose the reaction proceeds after a minute only. On adding the conc. sulphuric acid to glucose the solution turns yellow,which indicates that the conc. ${{H}_{2}}S{{O}_{4}}$ added is dehydrating the glucose molecule and then the formation of C takes place the dehydration reaction accelerates the process of C formation since the dehydration reaction is exothermic.
Glucose turns to C by removing the water molecule from glucose.
- The dil. ${{H}_{2}}S{{O}_{4}}$ is not a dehydrating agent,since it contains water molecules in them.
- Con. ${{H}_{2}}S{{O}_{4}}$ is diluted with water to form dil. ${{H}_{2}}S{{O}_{4}}$.
So the assertion statement is true as the con. ${{H}_{2}}S{{O}_{4}}$ is a dehydrating agent and the reason explains the assertion statement.
So, the correct answer is “Option A”.

Note: In glucose, dehydration reaction with conc. ${{H}_{2}}S{{O}_{4}}$, the heat produced convert the water molecules to steam and this heats up the C formed and C smoke appears like a snake growing from the reaction vessel.
- We always add acid to the container that has water, for the dilution of acid.
- Dilution of conc. ${{H}_{2}}S{{O}_{4}}$ is also an exothermic reaction.