Question

2.46 g of sodium hydroxide (molar mass = 40) is dissolved in water and the solution is made to 100 $c{{m}^{3}}$ in a volumetric flask. Calculate the molarity (in mol/L) of the solution.

Answer 1

Hint: Molarity of the solution can be defined as the amount of solute present in a liter of the solution. The concentration of the solution can be expressed as molarity and it can be denoted with a symbol M. The formula to calculate the molarity of the solution is as follows.
\[Molarity(M)=\dfrac{w}{MW}\times \dfrac{1000}{V(ml)}\]
Here W = weight of the solute
MW = Molecular weight of the solute
V = volume of the solution in ml.

Complete Solution :
- In the question it is given that to calculate the molarity of the solution contains 2.46 g of sodium hydroxide in 100 $c{{m}^{3}}$ of the solution.
- We know that 100 $c{{m}^{3}}$ = 0.1 liter
- The formula to calculate the molarity of the solution is
\[Molarity(M)=\dfrac{w}{MW}\times \dfrac{1000}{V(ml)}\]
Here W = weight of the solute = 2.46 g
MW = Molecular weight of the solute = 40
V = volume of the solution in ml 0.1 liter = 100 ml

- Substitute the known values in the above formula to get the molarity of the solution.
\[\begin{align}
  & Molarity(M)=\dfrac{w}{MW}\times \dfrac{1000}{V(ml)} \\
 & M=\dfrac{2.46}{40}\times \dfrac{1000}{100} \\
 & M=0.615M \\
\end{align}\]
- Therefore the molarity of the solution contains 2.46 g of sodium hydroxide in 100 $c{{m}^{3}}$ of the solution is 0.615 M.

Note: We can express the concentration of the solution in molarity and normality. In molarity we will consider the molecular weight of the solute but in normality we will consider the equivalent weight of the solute.