Question

2.5 litre of 1 M NaOH solution is mixed with another 3 litre of 0.5 M NaOH solution. Then find out molarity of resultant solution:

• A. 0.73 M
• B. 0.80 M
• C. 0.50 M
• D. 1.0 M

Answer 1

The correct option is A 0.73 M

Molecular weight of $NaOH=40gmo{l}^{-1}$
2.5 litre of $1MNaOH$ solution contain $40\times 1\times 2.5$
$=40\times 2.5gofNaOH$
3 litre of 0.5 M NaOH solution contain $40\times 0.5\times 3$
$=40\times 0.5\times 3gofNaOH$
If these two solutions are mixed, the volume of the
resultant solution = (2.5 + 3) = 5.5 litre.
5.5 litre of the resultant solution contain
$=40(2.5+1.5)gofNaOH$
1 litre of the resultant solution contain $\frac{40\times 4}{5.5}gofNaOH=\frac{40\times 4}{5.5\times 40}\text{mole}ofNaOH$
The molarity of the resultant solution = 0.727 ≈ 0.73 M