Question

You have 40 g of $MgC{{l}_{2}}$. How many atoms of $Cl$are there in sample?

Answer 1

Hint: An atom is consist of a nucleus and this nucleus is made up of protons which are positively charged and neutrons these are neutral in nature i.e. carries no charge and electrons carries negative charge are revolving around the nucleus.

Complete answer:
To calculate the number of atoms we first have to calculate the number of moles where s mole of a substance or particle can be defined as containing exactly $6.022\times {{10}^{23}}$ particles which may be atoms, molecules or ions where $6.022\times {{10}^{23}}$ is known as the Avogadro’s number.
$MgC{{l}_{2}}$ is generally known by the name magnesium chloride and molar mass i.e. sum of the the mass of all the atoms i.e. magnesium and two chlorine atoms present in magnesium chloride.
Now we know that the molar mass of magnesium is 25 and molar mass of chlorine is 35.5. Therefore, mass of $MgC{{l}_{2}}$= $6.022\times {{10}^{23}}\times 0.842=5.07\times {{10}^{23}}$$25+35.5\times 2=25+70=95$
Moles of $MgC{{l}_{2}}$in given sample can be calculated by the formula = $\dfrac{given\ \text{mass}}{molar\ \text{mass}}$
= $\dfrac{40}{95}=0.421mol$
Moles of chlorine atoms in given sample = $2\times 0.421mol=0.842mol$
Then number of chlorine atoms can be calculated as
1 mol of chlorine contains $6.022\times {{10}^{23}}$number of chlorine atoms, then
0.842 mol of chlorine contains $6.022\times {{10}^{23}}\times 0.842=5.07\times {{10}^{23}}$
Hence we can say that 40 g of $MgC{{l}_{2}}$ contains $5.07\times {{10}^{23}}$ atoms of $Cl$ in the given sample.

Note:
Mole is generally represented by the symbol mol. It is generally described as the unit of measurement for the amount of substance in SI where SI stands for International System of units. It is defined on the basis of Avogadro’s number.