Question

‌Calculate‌ ‌the‌ ‌number‌ ‌of‌ ‌moles‌ ‌in‌ ‌$52g$ of‌ ‌$He$‌ ‌(finding‌ ‌mole‌ ‌from‌ ‌mass).‌ ‌

Answer 1

This type of question is directly formula-based. Simply use the formula of the number of moles and put the given data and calculate the number of moles of $He$ asked in the question. Mass of $He$ and molar mass is known from the question.

Complete step-by-step answer: Given data:
Mass of $He$: $52g$
The molar mass of $He$: $gmo{l^{ - 1}}$
Using the given data in the number of moles formula we will get:
Number of moles $(n) = \dfrac{{{W_{He}}}}{{{M_{He}}}}\dfrac{{52}}{4} = 13mol$
So the number of moles in $52g$ of $He$ is $13mol$
Additional information: Relation between mole, mass and number of atoms:
Let’s refresh our memory of what a mole is. Just as a dozen is to 12 things a mole is to $6.022 \times {10^{23}}$ the number of anything if I had given you 4 dozen of sulphur you would have multiplied 4 by 12 to find the number of sulphur atoms. Now I have $4mol$ of sulphur. How many atoms do you think that there are in this sample? Since I am talking about $mole$ you can simply multiply 4 with $6.022 \times {10^{23}}$. We will get:

$$4 \times 6.022 \times {10^{23}} \\\ = 24.088 \times {10^{23}} \\\$$

It’s a pretty huge number that this sample contains. So in case, we have $5mol$ of sulphur to calculate the number of atoms present we will multiply $5mol$ with $6.022 \times {10^{23}}$ which gives us $3.011 \times {10^{23}}$ the number of sulphur atoms.
In general, if we have n moles then the number of atoms will be $n \times 6.022 \times {10^{23}}$or $n \times {N_A}$
Here ${N_A}$ is Avogadro's number

Note: Molar mass is equal to the sum of number of protons and number of neutrons. In $He$, there are two protons and two neutrons. That is why the molar mass of $He$ is $4amu$. We use unitary methods to solve these questions. Relationship between number of atoms and number of moles is given by:
Number of atoms= number of $moles \times {N_A}$