Question

In the gaseous state, chlorine exists as a diatomic molecule Cl2 (Molar mass = 70.9 g/mol).Calculate the number of moles of chlorine present in 140 g of chlorine gas.

Answer 1

Answer : The moles of chlorine present in 140 grams of chlorine gas are 3.96 moles.

Explanation : Given,

Mass of $Cl_2$ = 140 g

Molar mass of $Cl_2$ = 70.9 g/mol

Formula used :

$\text{Moles of }Cl_2=\frac{\text{Mass of }Cl_2}{\text{Molar mass of }Cl_2}$

Now put all the given values in this formula, we get:

$\text{Moles of }Cl_2=\frac{140g}{70.9g/mol}$

$\text{Moles of }Cl_2=1.98mol$

The number of moles of chlorine in $Cl_2$ = 2 × 1.98 = 3.96 mole

Therefore, the moles of chlorine present in 140 grams of chlorine gas are 3.96 moles.

Answer 2

1 mole = 70.9
X mole = 140
X=1.9746 moles
X= 1.98 when rounded to 3 significant figures.