Question

Volume of $0.1M\,{H_2}S{O_4}$ solution required to neutralize $40\,mL$ of $0.1M\,NaOH$ solution will be:
A. $40\,mL$
B. $39\,mL$
C. $20\,mL$
D. $10\,mL$

Answer 1

Hint:Acid (having pH less than 7) when reacts quantitatively with base (pH having more than 7), they form salt and water. And this reaction is well known as neutralization reaction. The pH of the neutralized reaction depends upon the acid strengths of reactants.

Complete answer:
The neutralization reaction can be represented as
Acid + base $\to$ salt + water
Simplest example of this reaction is when hydrochloric acid reacts with sodium hydroxide
$HCl + NaOH \to NaCl + {H_2}O$
The products formed are salt that is sodium chloride and water. Since both the acid and base are strong so this reaction is a strong acid- strong base neutralization reaction. In strong acid – strong base neutralization reaction, the pH of the resulting solution lies around pH 7. And the solution will be neutral.
For the above reaction-
${H_2}S{O_4} + 2NaOH \to N{a_2}S{O_4} + 2{H_2}O$
Here we can see that the basicity of sulphuric acid is 2. That means for $1\,mol$ of sulphuric acid we need $2\,mol$ of base to completely neutralize the acid.
We know that, ${N_{acid}}{V_{acid}} = {N_{base}}{V_{base}}$
Given ,
$N_{acid} = 0.1 \times 2 = 0.2\,N$
$N_{base} = 0.1\,N$
$V_{base} = 40\,mL$
We have to calculate the volume of acid required.
Putting all the values in the above equation
$
\Rightarrow 0.2 \times {V_{acid}} = 1.0 \times 40 \\
\Rightarrow {V_{acid}} = 20\,mL
 $
So the volume of sulphuric acid required to neutralize the base is $20\,mL$

Hence the correct option will be C. $20\,mL$

Note:
But if we have strong acid - weak base or strong base - weak acid then the pH of the resulting solution will depend on the salt that has formed. Either the salt formed will be acidic salt or basic salt. The formation of acidic salt when acid will be stronger, and basic salt when base will be stronger.