Question

What is a gram molecule? And gram equivalent? Give an example.

Answer 1

Hint : These are no longer in use in our day to day life for communication purposes or even in the industries.However, these terms are used in stoichiometry. These are similar in meaning to each other but officially there is a difference.

Complete Step By Step Answer:
A gram molecule can be defined as the number of grams of a substance which is the same as the relative molecular mass of that particular substance. For better understanding take this as an example, basically one mole of $CaC{{O}_{3}}$ contains five grams of atoms that is one of Ca, one of C and three of O, also one gram molecule and then two gram ions (as it has one of $C{{a}^{2+}}$ and one $C{{O}_{3}}^{2-}$)
In chemistry, we define a mole as the amount of a substance that contains exactly $6.02214076\text{ }*\text{ }{{10}^{23}}$molecules, ions, monatomic/polyatomic ions and other particles like electrons of the given substance.
The number $6.02214076*10^{23}$ is popularly referred to as the Avogadro constant or Avagadro’s number and is denoted by the symbol ${{N}_{A}}$.
A gram equivalent is defined as the number of grams that is equivalent to one gram of hydrogen which means that it can react with or replace one gram of hydrogen easily. This is not the same as the above!
For Equivalent weight we use the formula given below:
Equivalent Weight = E
Molecular Weight = ${{M}_{O}}$
Valence Factor = X
So Equivalent Weight is given by:
Equivalent Weight= $\frac{Molecular\text{ }Weight}{Valence\text{ }Factor}$
Or, E= $\frac{{{M}_{O}}}{X}$
Take this example to understand better: The gram equivalent for oxygen is nearly $8g$, while a mole of oxygen atoms would have it nearly $16g$ and a mole of oxygen molecules will be around $32g$

Note :
It is not compulsory that the number of moles of a molecule will always be equal to the number of moles of its constituent elements. It depends on various conditions and situations and will vary accordingly.