Question

Solution(s) containing 40 gm NaOH is/are
A.50 gm of $80\%$ (w/w) NaOH
B.50 gm of 20 M $NaOH\left[ {{d_{so\ln }} = 1\,\,gm/ml} \right]$
C.50 gm of $80\%$ (w/v) $NaOH\,\,\left[ {{d_{soln}} = 1.2\,\,gm/ml} \right]$
D.50 gm of 5m NaOH

Answer 1

First of all, we should know the solution(s) containing 40 g of NaOH i.e., 40 g in 100 gm of the solution and also the molecular weight of NaOH is $\left( {23 + 16 + 1} \right) = 40$. Now, we will see if each option is equal to solution(s) containing 40 gm NaOH in the step -by- step answer.

Complete answer:
A.Given in the question is solution(s) containing 40 gm NaOH
$40\%$ by weight means 40gm of NaOH in 100 gm solution.
50g in $80\%$ (w/w) NaOH
Which means, $50 \times 80/100 = 40$

B.50g of 20 M $NaOH\,\,\left[ {{d_{soln}} = 1\,\,gm/ml} \right]$
20 mol in 1Litre
$20 \times 40$in 1000g
800g in 1000g
$800/1000 \times 50 = 40$

C.80 percent NaOH
80g in 100ml
80g in $100 \times 1.2 = 120g$
$80/100 \times 50$ $= 100/3$ $= 33.33$
33.33 is definitely not 40

D.50gm of 5M NaOH
50 mol in 1000g solvent
$5 \times 40$ $= 200g$ NaOH in $1000 + 200$ that is 12000 = 12000g solution
$50 \times 200/1200 = 8.33$
8.33 is definitely not 40

Therefore, the correct answers are options (A) and (B).

Note:
With increase in dilution, the number of moles per unit volume decreases and the molarity of the solution is the number of moles of solute per unit volume of solution.
Molarity (M) is the amount of a substance in a certain volume of solution. Molarity is defined as the moles of a solute per litres of a solution. Molarity is also known as the molar concentration of a solution.