Question

How many atoms are in $1.54$moles of bromine $(Br)$?

Answer 1

Hint: The question is based on the concept of number of moles and the Avogadro Law. According to the Avogadro law $1$mole of every substance occupies $22.4L$of volume at STP and contains $6.023\times {{10}^{23}}$number of molecules/particles. Hence Avogadro law gives the value of the number of molecules present in $1$mole of a substance. So, in order to find the number of molecules in more than one mole we will simply perform the unitary method. Once the number of molecules is calculated then the number of atoms can be calculated by simply multiplying the number of molecules by its atomicity.

Complete step-by-step answer:
By using the principle of Avogadro law, we can say that
Number of molecules in mole of Bromine $(Br)\,=\,6.023\times {{10}^{23}}$
Therefore, number of molecules present in $1.54$moles of Bromine $(Br)$will be given by
$
\Rightarrow \,1.54\,\times \,6.023\times \,{{10}^{23}} \\
 \Rightarrow \,9.28\,\times \,{{10}^{23}}\,molecules \\
$
Now we know that atomicity of the Bromine molecule $(Br)$is $2$. It means one molecule of bromine contains $2$atoms as it is a diatomic molecule.
$\because $Number of atoms in $1$molecule of Bromine = $2$atoms
$\therefore $Number of atoms in $9.28\,\times \,{{10}^{23}}$molecules = $9.28\,\times \,{{10}^{23}}\times \,2$= $18.56\,\times \,{{10}^{23}}$atoms

Hence $1.54$moles of Bromine $(Br)$contains $18.56\,\times \,{{10}^{23}}$atoms.

Note: Do not commit mistakes by taking the number of molecules as number of atoms. This is the most misunderstood fact. By this misconception of atoms and molecules sometimes students leave the question in the mid-way and do not solve the entire question. For calculating the number of atoms in an element always multiply the number of molecules with the atomicity of the element. Perform the mathematical calculations carefully.