Question

The molarity of the solution containing $2.8\% (m/v)$ solution of $KOH$ is: (given atomic mass of $K = 39$ )
(A) $0.1M$
(B) $0.5M$
(C) $0.2M$
(D) $1M$

Answer 1

Hint : In order to answer this question, to calculate the molarity of the given solution, we will first find the weight of $KOH$ and then we will find the number of moles. And finally we can apply the formula of molarity.
$Molarity = \dfrac{{No.\,of\,moles}}{{Volume}} = \dfrac{n}{V}$

Complete Step By Step Answer:
$2.8\% (m/v)$ solution of $KOH$ means $2.8g$ of solute in $100ml$ of solution.
So, the weight of $KOH$ $= 2.8g$
And, the volume of the solution is $100ml$ .
Number of moles in $KOH$ $= 2.8 \times 1000$
Now, we can apply the formula to find the molarity of the given solution:-
$\because Molarity = \dfrac{{No.\,of\,moles}}{{Volume(l)}} \\\ \,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\, = \dfrac{{2.8 \times 1000}}{{56 \times 100}} = \dfrac{{28}}{{56}} = 0.5M \\\$
Therefore, the molarity of the solution containing the $2.8\% (m/v)$ solution of $KOH$ is $0.5M$ .
Hence, the correct option is (B) $0.5M$ .

Note :
One of the most popular measures used to quantify the concentration of a solution is molarity , which shows the number of moles of solute per litre of solution. Molarity is a unit of measurement that can be used to determine the volume of a solvent or the amount of a solute.