Question

Molarity of 0.1 N oxalic acid is:
(A) 0.05 M
(B) 0.1 M
(C) 0.2 M
(D) 0.3 M

Answer 1

Hint: Both normality and molarity are measures of concentration in a solution. The molarity is a measure of the number of moles per liter of solution, and the second one is a quantity, which depends on the solution's role in the reaction.


Complete step by step solution:
  - Let's start with the concepts of molarity and normality. As we know, molarity is the most commonly used measure of concentration and it is usually expressed as the number of moles of solute per liter of solution.
 - Thus, the molarity can be defined as the number of moles of solute dissolved in one liter or one cubic decimeter of the solution. The unit of molarity is given as $mol{L}^{-1}$ or $mold{m}^{-3}$.
 - Normality differs from molarity and it can be defined as a measure of concentration that is equal to the gram equivalent weight per liter of solution. Here the gram equivalent weight is a measure of the reactive capacity of a molecule and the solution's normality is determined by the role of solution in reaction.
 - We can interconvert the normality and molarity by using the given equation
Normality = Molarity × n factor
      As we know, the acids are formed when the hydrogen ($H^{+}$) ions are dissolved in a solvent. In a reaction, the number of $H^{+}$ ions that get replaced by 1 mole of an acid is known as the n-factor of that acid. For oxalic acid ($C_2{H}_2{O}_4$) we can write this chemical equation as follows

$HOOC-COOH\to {2CO}_2+{2H}^{+}+2e^{-}$
 Since two $H^{+}$ is involved in this reaction, the n factor is found as 2.
  Thus, by substituting the given value of normality and n factor in the relation of normality and molarity, we can write the relation as follows
      0.1= Molarity× 2
  Hence, Molarity =${\displaystyle \frac{0.1}{2}}$
                              = 0.05 M

Therefore, the answer is option (A). That is, the molarity of 0.1 N oxalic acid is 0.05 M.


Note: Do not confuse molarity with molality. As we mentioned, molarity of a given solution can be defined as the number of moles of solute per litre of solution whereas molality can be defined as the total moles of a solute which is contained in a kilogram of a solvent. The first parameter depends on the volume of solution and the second one depends on the mass of the solvent.