Question

Calculate the mass of oxalic acid $\left( {{H_2}{C_2}{O_4}.2{H_2}O} \right)$ is needed to prepare $250ml,1M$ aqueous solution of oxalic acid. I got $15g$ . Is my answer correct?

Answer 1

Volume and molarity which is nothing but the concentration was given. Calculate the molar mass from the given formula, by substituting the molar mass, volume, and molarity in the below formula gives the mass of oxalic acid.
$M = \dfrac{w}{m} \times \dfrac{{1000}}{V}$
$M$ is molarity
$V$ is volume of solution
$m$ is molar mass
$w$ is the weight of oxalic acid.

Complete Step By Step Answer:
Given that oxalic acid has the molecular formula of ${H_2}{C_2}{O_4}.2{H_2}O$ , from the molecular formula,
The molar mass of carbon is $12gmo{l^{ - 1}}$
The molar mass of hydrogen is $1gmo{l^{ - 1}}$
The molar mass of oxygen is $16gmo{l^{ - 1}}$
Thus, the total molar mass of oxalic acid will be $6\left( 1 \right) + 2\left( {12} \right) + 4\left( {16} \right) = 126gmo{l^{ - 1}}$
Given volume of oxalic acid is $250ml$
The given molarity of oxalic acid is $1M$
By substituting the molar mass, volume, and molarity in the above formula, the mass of oxalic acid can be determined.
$1 = \dfrac{w}{{126}} \times \dfrac{{1000}}{{250}}$
By further simplification of the above value, the mass of oxalic acid will be $31.5gm$
Thus, $31.5gm$ of oxalic acid $\left( {{H_2}{C_2}{O_4}.2{H_2}O} \right)$ is needed to prepare $250ml,1M$ aqueous solution of oxalic acid.
From $15g$ of oxalic acid the $250ml,1M$ aqueous solution of oxalic acid cannot be prepared.
Thus, $15g$ is not a correct answer.

Note:
While calculating the molarity or related terms like mass of substance from molarity, the volume of the solution must be taken in litres only, if it is in millilitres, multiply the obtained molarity by $1000$ or convert the millilitres into volume by taking $1litre$ equal to $1000ml$ .