Question

Calculate the mass of $2.5$ gram atoms of oxygen.

Answer 1

Oxygen is an element with atomic number $8$ and has atomic mass of $16$ atomic mass units. Given that the mass of an oxygen atom is $2.5$ gram atoms which means $2.5$ moles of oxygen. By substituting the moles as $2.5$ and molar mass of oxygen atoms as $16$ gives the mass of $2.5$ gram atoms of oxygen.
$n = \dfrac{w}{M}$
$n$ is number of moles
$w$ is mass
$M$ is molar mass.

Complete answer:
Chemical elements are arranged in the periodic table according to the increase in atomic numbers. Elements are arranged in vertical columns and horizontal rows. The vertical columns were known as groups and the horizontal rows were known as periods.
Oxygen belongs to the group ${16^{th}}$ and ${2^{nd}}$ period. It has an atomic number of $8$ . The molar mass of an oxygen atom is $16$ atomic mass units.
Given that oxygen has a mass of $2.5$ gram atoms. The mass of $2.5$ gram atoms mean $2.5$ moles.
The number of moles of that compound is the ratio of mass to molar mass of that compound.
Substitute the moles as $2.5$ and molar mass as $16$ .
$2.5 = \dfrac{w}{{16}}$
By simplification, the mass will be $40$ grams.
Thus, the mass of $2.5$ gram atoms of oxygen will be $40$ grams.

Note:
Mole is the quantity that represents the number of atoms or particles or ions present in one mole. It is used to express a very small value. Gram atoms are nothing but moles. Thus, the mass of $2.5$ gram atoms is nothing but moles. Substitute them in place of moles. The molar mass should be taken exactly.