Question

If the 1.58g of \[KMn{O_4}\] in acidic medium completely reacts with ferrous oxalate what weight (in gm) of ferrous oxalate is required?
A. 2.73g
B. 4.73g
C. 11.19g
D. 5.62g

Answer 1

Hint: The mass of an atom is measured in atomic mass (ma or m). Although the kilogramme (symbol: kg) is the SI unit of mass, atomic mass is frequently represented in the non-SI unit dalton, which is defined as 12 times the mass of a single carbon-12 atom at rest. The nucleus' protons and neutrons account for virtually all of an atom's total mass, with electrons and nuclear binding energy playing a modest role. As a result, when stated in daltons, the numeric value of the atomic mass is approximately equal to the mass number.

Complete answer:
The mass of one equivalent (also known as the gramme equivalent) is the mass of a given material that will mix with or displace a fixed quantity of another substance. The mass of an element that combines with or displaces 1.008 grams of hydrogen, 8.0 grams of oxygen, or 35.5 grams of chlorine is its equivalent weight. These figures are calculated by dividing the atomic weight by the typical valence; for oxygen, this is 16.0 g / 2 = 8.0 g.
${\text{Equivalent mass = }}\dfrac{{{\text{Molecular mass}}}}{{{\text{n factor}}}}$
${\text{Fe}}{{\text{C}}_2}{{\text{O}}_4} \Rightarrow {{\text{n}}_{\text{f}}} = 3$
${\text{KMn}}{{\text{O}}_4} \Rightarrow {{\text{n}}_{\text{f}}} = 5$
Using ${\text{No of moles = }}\dfrac{{{\text{Given mass}}}}{{{\text{Molecular mass}}}}$
Moles of ${\text{KMn}}{{\text{O}}_4} = \dfrac{{1.58}}{{158}} = 0.01$
Equivalents of ${\text{KMn}}{{\text{O}}_4} = moles \times {{\text{n}}_{\text{f}}} = 0.01 \times 5 = 0.05$
Equivalents of ${\text{Fe}}{{\text{C}}_2}{{\text{O}}_4} = moles \times {{\text{n}}_{\text{f}}} = {\text{n}} \times 3 = 0.05$
$ \Rightarrow {\text{n}} = \dfrac{{0.05}}{3}$
Weight of ${\text{Fe}}{{\text{C}}_2}{{\text{O}}_4} = {\text{n}} \times 142 = 2.73{\text{gm}}$

So, the correct answer is “Option A”.

Note:
Unlike atomic weight, which is dimensionless, equivalent weight contains dimensions and units of mass. Equivalent weights were previously established through experiment, but are now calculated from molar masses (to the extent that they are still utilised). The equivalent weight of a compound may also be determined by dividing the molecular mass by the amount of positive or negative electrical charges produced by the molecule's dissolution.