Question

Assertion: In the titration of $N{a}_{2}C{O}_3$ with HCl using methyl orange indicator, the volume of the acid required at the equivalence point is twice that of the acid required using phenolphthalein as indicator.
Reason: Two moles of HCl are required for the complete neutralisation of one mole of $N{a}_{2}C{O}_3$.

• 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. Assertion is incorrect but Reason is correct
• E. Both Assertion and Reason are incorrect

Answer 1

The correct option is B Both Assertion and Reason are correct but Reason is not the correct explanation for Assertion

In the titration of $N{a}_{2}C{O}_3$ with HCl using methyl orange indicator, the volume of the acid required at the equivalence point is twice that of the acid required using phenolphthalein as indicator.

This is because of the fact that phenolphthalein is a weak organic acid, and it changes its colour in weakly basic medium $NaHC{O}_3$, so as soon as the $N{a}_{2}C{O}_3$ is converted to $NaHC{O}_3$ phenolphthalein shows the colour change indicating the completion of the reaction.

However, in the presence of methyl orange, all the basic substances left in the mixture will be neutralized by acid and methyl orange will show the colour change when the medium is weakly acidic. $(H_{2}O+C{O}_{2}i.e.H_{2}C{O}_3).$