Question

How many moles of sulphur are in $1.81\times {{10}^{24}}$ atoms of sulphur?

Answer 1

We are already provided with the element. We need to find out the number of moles. For that we need the basic formula of mole concept. It is a part of physical chemistry.

Formula used: $\text{no of moles =}\dfrac{\text{given atoms}}{\text{Avagadro number}}$
Here Avogadro number is $6.023\times {{10}^{23}}$ .

Complete step by step answer
We already know that:
In 1 mole of sulphur atoms, there are $6.023\times {{10}^{23}}$ individual sulphur atoms present.
So, $\text{no of moles =}\dfrac{\text{given atoms}}{\text{Avagadro number}}$
$=\dfrac{1.81\times {{10}^{24}}}{6.023\times {{10}^{23}}}=3$
So, there are 3 moles of sulphur in $1.81\times {{10}^{24}}$ atoms of sulphur.
Additional Note: We should know that in order to calculate the number of moles of any substance present in the sample, we simply divide the given weight of the substance by its molar mass. Where 'n' is the number of moles, 'm' is the given mass and 'M' is the molar mass. A mole is defined as the mass of the substance which consists of the equal quantity of basic units. Example atoms in 12 grams are the same as 12C. The basic units can be molecules, atoms or formula units based on the substance.
A mole fraction indicates the number of chemical elements. One mole of any substance is equal to the value of $6.023\times {{10}^{23}}$ (Avagadro number). It can be used to measure the products obtained from the chemical reaction. The unit is denoted by mol.

Note
We should also know that here we are dealing with sulphur atoms and not sulphur molecules.
We already know that to know how many moles of a material you have, divide the mass of the material by its molar mass. The molar mass of a substance is the mass in grams of one mole of that substance.