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.