Question

One litre of $0.15$ M HCl and one litre of $0.3$ M HCl is given. What is the maximum volume of $0.2$ M HCl which one can make from these two solutions? No water is added.

• A. $1.2$ L
• B. $1.5$ L
• C. $1.3$ L
• D. $1.4$ L

Answer 1

The correct option is B $1.5$ L

Since, no water added, volume of solution cannot exceed $2$ L.

So, less concentrated solution should be taken in its total volume.
Only the small portion of more concentrated solution is to be mixed so that the total concentrated is less than $0.3$ M HCl.
Let $x$ L of $0.3M$ solution is mixed.
Total volume $=(x+1)$ L

$M_1{V}_1+M_2{V}_2=M_3{V}_3$ [$V_3=(1+x)$ L]
$0.3\times x+0.15\times 1=M_3(1+x)$
Final molarity $=0.2M$
$0.3x+0.15=0.2(1+x)$
$x=0.5$ L
Maximum volume $=1+0.5=1.5$ L