Question

1 L of NaOH solution contains 4.0 g of NaOH. The concentration of the solution is:
A. 0.4N
B. 4.0N
C. 0.1N
D. 1.0N

Answer 1

Hint: To calculate the concentration of the solution in terms of normality, first we need to find out the molarity of the solution. The relation between normality and molarity is that normality is equal to n-factor multiplied by the molarity.

Complete step by step answer:
Given,
Volume of NaOH is 1 L.
The mass of NaOH is 4.0 g.
The molar mass of NaOH is 40 g/mol.
The formula for calculating the number of moles is shown below.
$n = \dfrac{m}{M}$
Where,
n is the number of moles.
m is the given mass
M is the molar mass
To calculate the number of moles of sodium hydroxide (NaOH), substitute the values of mass and molar mass in the above equation.
$\Rightarrow n = \dfrac{{4.0g}}{{40g/mol}}$
$\Rightarrow n = 0.1mol$
The molarity of the solution is defined as the number of moles of solute dissolved in one litre of solution.
The formula to calculate molarity is shown below.
$M = \dfrac{n}{V}$
Where,
M is the molarity
n is the number of moles
V is the volume in litres
To calculate the molarity of the solution, substitute the values of moles and volume in the above equation.
$\Rightarrow M = \dfrac{{0.1mol}}{{1L}}$
$\Rightarrow M = 0.1mol/L$
The normality of the solution is defined as the gram equivalent weight of the solute dissolved in one litre solution.
The relation between normality of the solution and molarity of the solution is shown below.
$normality = n - factor \times molarity$
For any base compound, the n-factor is defined as the number of replaceable hydroxide ions present which can be replaced by 1 mole of base during the reaction.
The dissociation reaction of sodium hydroxide is shown below.
$NaOH \to N{a^ + } + O{H^ - }$
In sodium hydroxide only one hydroxide ion is present which can be replaced. Therefore, the value of n-factor is 1.
To calculate the normality, substitute the values in the equation.
$\Rightarrow Normality = 1 \times 0.1$
$\Rightarrow Normality = 0.1N$
Thus, the concentration of the solution is 0.1N.
So, the correct answer is “Option C”.

Note:
Normality is also calculated by gram equivalent divided by the volume of solution. The gram equivalent weight is calculated by dividing molecular weight by the n-factor.