Question

What mass of ${H_2}{C_2}{O_4}.2{H_2}O$ (mol mass $ = 126$ ) should be dissolved in water to prepare $250mL$ of a centinormal solution which acts as a reducing agent?
A. $0.63g$
B. $0.1575g$
C. $0.126g$
D. $0.875g$

Answer 1

Hint: Centinormal is a unit of concentration of a solution that is equal to one hundredth of normal. In a redox chemical process, a reducing agent is an element or molecule that loses an electron to an electron recipient (oxidising agent).
Formula used:
Equivalent weight = Molecular weight
                                 Number of equivalent moles

Complete answer:
Per mole of given acid ${C_2}O_4^{2 - }$ present $ = 1mole$
${C_2}{O_4} \to C{O_2} + 2{e^ - }$
Therefore, X factor for ${H_2}{C_2}{O_4}.2{H_2}O$ as a reducing agent $ = 2$
Hydrated oxalic acid has a molar mass of 126 grammes per mole. Because oxalic acid's chemical formula is $COOH - COOH$ , it's clear that it's a dibasic acid with the ability to contribute two ${H^ + }$ ions. As a result, the following formula can be used to calculate the equivalent weight of oxalic acid:
Equivalent weight = Molecular weight
                                 Number of equivalent moles
Because one mole of oxalic acid can release two moles of H+ ions and neutralise two moles of OH– ions, the number of equivalent moles is two. As a result, the oxalic acid equivalent weight can be computed as follows:
Equivalent weight $ = \dfrac{{126}}{2} = 63$
$250ml$ of centinormal solution $ = \dfrac{{250}}{{100 \times {{10}^{ - 3}}}}$
Equivalent weight of ${H_2}{C_2}{O_4}.2{H_2}O$ required $ = \dfrac{{250}}{{{{100}^{ - 3}} \times {{10}^{ - 3}} \times 63}}$
Equivalent weight of ${H_2}{C_2}{O_4}.2{H_2}O$ required $ = 0.1575g$
So, the correct answer is “Option B”.

Note:
Oxalic acid has the chemical formula ${C_2}{H_2}{O_4}$ and is a dicarboxylic acid. Ethanedioic acid is another name for it. Oxalic acid is a weak acid that will only partially ionise in an aqueous solution. Oxalic acid has two protons that are acidic. The first ionisation produces $H{C_2}O_4^ - $, a weak acid that will also ionise.