Question

Molarity of $4\%$(w/v)solution of NaOH is:
A.$0.1$
B.$0.5$
C.$0.01$
D.$1.0$

Answer 1

As we know that Molarity of a substance is defined as number of moles of the solute to the volume of the solution in litres so we will calculate using this only.

Complete step-by-step answer: Molarity of a substance is defined as number of moles of the solute to the volume of the solution in litres
Now we will talk about the question what is given to us
We are given $4\%$ (w/v) solution of NaOH which means that there are $4gms$ of NaOH is dissolved in $100ml$ of water
Then we are here talking about the molarity so the molarity of NaOH is what we need to calculate. Now as we know that molarity=number of moles of solute/volume of the solution
Then in order to calculate the molarity we need to know the number of moles for this then ,
The given weight is $4gms$
Molar mass of NaOH is $40gmo{l^{ - 1}}$
For calculating the number of moles of solute which is given as given mass/ molar mass
Then on substituting the values we get $4/40 = 1/10 = 0.1$
So we get $0.1moles$ as the number of moles.
Then for finding molarity another thing we need is volume of the solution In litres and we know the volume of the solution is $100ml$ which we need to convert into litres and to do so we will divide it by thousand in order to get in litres.
Then molarity is calculated as $\frac{{0.1}}{{0.1}} = 1M$
So according to this we find out the molarity to be one . hence,the last option is correct.

Note: We should know that the solute is always present in small amounts and solvent in larger amounts.