Question

A solution is prepared by dissolving 4g of NaOH in distilled water to give

200ml of solution.Molarity of solution is:

(a) 0.5M (b) 0.1M (c) 0.05M (d) 0.2M​

Answer 1

Given:

A solution is prepared by dissolving 4g of NaOH in distilled water to give 200ml of solution.

To find:

Molarity of the solution

Solution:

$Number of moles (n) = \frac{mass (given)}{Molar mass}$

⇒ $n = \frac{4}{40} = 0.1$.............................(a)

$Molarity (M) = \frac{n}{V}$ ..............(b)

(where n is the number of moles and V is the volume of the solution in liters)

Since the volume of the solution is 200 ml (given)

⇒$Volume (litres)= \frac{200}{1000} = 0.2 l$

Putting the value of n and V in eq (b), we get

⇒ $M = \frac{0.1}{0.2} = 0.5 g/l$

Hence, molarity of the given NaOH solution is 0.5 g/l

Answer 2

Given:

A solution is prepared by dissolving 4g of NaOH in distilled water to give 200ml of solution.

To find:

Molarity of solution ?

Calculation:

Molarity refers to the number of moles of a substance dissolved in 1 litre of solution.

So, first let's calculate the moles of NaOH:

$\sf \therefore \: moles = \dfrac{given \: mass}{molar \: mass}$

$\sf \implies \: moles = \dfrac{4}{23 + 16 + 1}$

$\sf \implies \: moles = \dfrac{4}{40}$

$\sf \implies \: moles = 0.1$

Now, let's calculate the molarity :

$\sf \therefore \: molarity = \dfrac{moles}{volume \: of \: solution}$

$\sf \implies \: molarity = \dfrac{0.1}{( \frac{200}{1000} )}$

$\sf \implies \: molarity = \dfrac{0.1}{0.2}$

$\sf \implies \: molarity = \dfrac{1}{2}$

$\sf \implies \: molarity = 0.5 \: M$

So, molarity of solution is 0.5 M.