Question

An unknown chlorohydrocarbon has $3.55\%$ of chlorine. If each molecule of hydrocarbon has one chlorine atom only, then chlorine atoms present in $1g$ of chlorohydrocarbon are:
$\text{Atomic weight of}Cl=35.5u$
Avogadro constant, $N_A=6.023\times {10}^{23}$

• A. $6.023\times {10}^9$
• B. $6.023\times {10}^{23}$
• C. $6.023\times {10}^{21}$
• D. $6.023\times {10}^{20}$

Answer 1

The correct option is D $6.023\times {10}^{20}$

An unknown chlorohydrocarbon has 3.55% of chlorine.
100 g of chlorohydrocarbon has 3.55 g of chlorine.
1 g of chlorohydrocarbon will have $3.55\times \frac{1}{100}=0.0355g$ of chlorine.
$\text{Atomic weight of}Cl=35.5u$
$\text{Number of moles of}Cl=\frac{0.0355g}{35.5g/mol}=0.001mol$
$\text{Number of atoms of}Cl=0.001mol\times 6.023\times {10}^{23}mo{l}^{-1}=6.023\times {10}^{20}$
Hence, option D is correct.