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.