Question

The volume of $10\,N$ and $4\,N\, HCl$ required to make $1$ litre of $7\,N \,HCl$ are

• A. $0.75$ litre of $10\,N \,HCl$ and $0.25$ litre of $4\,N \,HCl$
• B. $0.80$ litre of $10\,N\, HCl$ and $0.20$ litre of $4\,N \,HCl$
• C. $0.60$ litre of $10\,N \,HCl$ and $0.40$ litre of $4\,N \,HCl$
• D. $0.50$ litre of $10\,N \,HCl$ and $0.50$ litre of $4\,N \,HCl$

Answer 1

Answer: (D)

$0.50$ litre of $10\,N \,HCl$ and $0.50$ litre of $4\,N \,HCl$

Answer 2

Let $V$ litre of $10 \,N\, HCI$ be mixed with $(1-V)$ litre of 4

$N\, HCl$ to give $(V+1-V)=1 L$ of $7 N HCl$
$N_{1} V_{1}+N_{2} V_{2} =NV$
$10 V+4(1-V) =7 \times 1$
$10 V+4-4 V =7$
$6 V =7-4$
$V =\frac{3}{6}=0.50\, L$

Volume of $10 \,N \,HCI =0.50 L$

Volume of $4 N HCl =1-0.50 =0.50 \,L$