Question

What is the equivalent weight of $Calcium{\text{ }}carbonate$( $CaC{O_3}$)?

Answer 1

The molecular mass and equivalent weight of a compound are not always the same. The equivalent weight is obtained by dividing the molecular weight of the compound to its charge present on the compound.

Complete answer:
Molecular weight, also known as the molecular mass or molar mass of a compound, is based on a $12$ as the atomic weight of$carbon - 12$. It is calculated in practise by summing the atomic weights of the atoms making up the substance’s molecular formula. It varies from $1$ like in $Hydrogen$ to millions in compounds like protein.
Different molecules of a same compound may have different molecular masses because they contain different isotopes of an element. The unit for molar mass is $g/mol$. The related quantity relative molecular mass, is defined as the ratio of the mass of a molecule to the unified atomic mass unit.
Molecular mass is calculated from the atomic masses of each nuclide present in the molecule, while molar masses are calculated from the standard atomic weights of each element.
The reason why we should know the molecular weight is because the equivalent weight of a compound is related to it.
Equivalent weight is the number of substances that completely react with each other in the reaction. It means the mass of one equivalent mass of a given substance which will combine with or displace a fixed quantity of another. It is given by the formula
$Equivalent{\text{ }}weight = \dfrac{{Molecular{\text{ }}weight}}{{valency}}$
Now that we are familiar with the required terms, let us calculate the equivalent weight of $CaC{O_3}$
First we will find the molecular weight of $CaC{O_3}$, for that we will require the atomic weight of the atoms present in $CaC{O_3}$
Atomic weight of $Ca = 40$
Atomic weight of $C = 12$
Atomic weight of $O = 16$
Molecular weight of $CaC{O_3}$= 40 + 12 + 3(16)$$$$ = 100
Charge on $CaC{O_3}$= C{a^{2 + }} + CO_3^{2 + }$$$$ = 2
Placing these value in the equivalent weight formula
$= \dfrac{{100}}{2} = 50$
Therefore the equivalent weight of $CaC{O_3}$ is 50$$$$g.

Note:
Equivalent weight is also known as gram equivalent, is the mass of one equivalent that is the mass of a given substance which will combine with or displace a fixed quantity of another substance. The equivalent weight of an element is the mass which combines with or displaces 1.008$$$$g of $Hydrogen$ or $35.5g$ of $Chlorine$.