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

Options

(a) 0.80 M
(b) 1.0 M
(c) 0.73 M
(d) 0.50 M

Correct Answer:

0.73 M

Explanation:

Molecular weight of NaOH = 40.
2.5 litre of 1 M NaOH solution contain 40⨯ 2.5 g of NaOH .
3 litre of 0.5 M NaOH solution contain 40 ⨯ 0.5⨯ 3 g of NaOH.
If this two solutions are mixed, the volume of the resultant solution = (2.5 + 3) lit = 5.5 litre.
5.5 litre of the resultant solution contain 40(2.5 + 1.5) g of NaOH.
1 litre of the resultant solution contain
40⨯4/5.5 g of NaOH = 40⨯4/5.5⨯40 mole of NaOH.
The molarity of the resultant solution = 0.727 ≈ 0.73 mol/L.