Question

$252{\text{ }}grams$ of oxalic acid with molecular formula ${C_2}{H_2}{O_4}.2{H_2}O$ dissolved in water to form 250ml. of the solution. Its molarity will be:

$${A.{\text{ }}16M} \\\ {B.{\text{ }}8M} \\\ {C.{\text{ }}32M} \\\ {D.{\text{ }}24M}$$

Answer 1

Hint : We have to calculate the number of moles of oxalic acid and then divide it by amount of water in litre.
Formula Used: $Molarity{\text{ }}\left( M \right)\; = {\text{ }}\dfrac{{Number{\text{ }}of{\text{ }}moles{\text{ }}of{\text{ }}solute}}{{Volume{\text{ }}of{\text{ }}solution{\text{ }}in{\text{ }}liters}}$

Complete step by step solution :
Let’s start with discussing the concept of molarity, molarity is defines as the number of moles in solute per litre of solution. It is also termed as molar concentration of a solution.
We are given with $252{\text{ }}g$ of oxalic acid; also we can calculate the molar mass of oxalic acid from its molecular formula. Molecular formula of oxalic acid is ${C_2}{H_2}{O_4}.2{H_2}O$ and the molar weight of each atom present is $C = 12g,{\text{ }}H = 1g,{\text{ }}O = 16g$
Molar mass of oxalic acid$= {\text{ }}\left( {12{\text{ }}X{\text{ }}2} \right){\text{ }} + {\text{ }}\left( {1{\text{ }}X{\text{ }}2} \right){\text{ }} + {\text{ }}\left( {16{\text{ }}X{\text{ }}4} \right){\text{ }} + {\text{ }}\left( {18{\text{ }}X{\text{ }}2} \right){\text{ }} = {\text{ }}126{\text{ }}grams$
So, 1 mole of oxalic acid is having a mass of$126{\text{ }}grams$.
Let’s calculate the number of moles of oxalic acid present in $252g$ of oxalic acid.
Moles of oxalic acid = $\dfrac{{Given{\text{ }}mass}}{{Molar{\text{ }}mass}} = \dfrac{{252}}{{126}} = 2{\text{ }}moles$
Now, we are having 2 moles of oxalic acid in $250{\text{ }}ml$of water. We can write $250{\text{ }}ml$ as $0.25{\text{ }}litre$of water. So, the molarity of the solution will be given by
$Molarity{\text{ }}\left( M \right)\; = {\text{ }}\dfrac{{Number{\text{ }}of{\text{ }}moles{\text{ }}of{\text{ }}solute}}{{Volume{\text{ }}of{\text{ }}solution{\text{ }}in{\text{ }}liters}}$
Molarity of solution = $\dfrac{2}{{0.25}} = 8{\text{ }}M$

So, we can conclude that the answer to this question is option B. $8{\text{ }}M$

Note : We must know that molarity is the concept which is widely used in chemistry and related fields. It is used to develop a particular solution of defined concentration. These solutions are made in a volumetric flask and are used in various experiments. In short, the concept of molarity is a very important concept from a practical point of view.