Question

The volume of a gas at STP is $1.12\times {10}^{-7}\text{cc}$. The number of molecules in it will be:

• A. $3.1\times {10}^{20}$
• B. $3.01\times {10}^{12}$
• C. $30.1\times {10}^{13}$
• D. $3.01\times {10}^{24}$

Answer 1

The correct option is B $3.01\times {10}^{12}$

Volume of 1 mole of gas at STP is $22.4\text{L}$ or $22400\text{mL}$ or $22400\text{cc}$
$22400\text{mL}$ of gas contains $6.023\times {10}^{23}$ molecules
$1.12\times {10}^{-7}\text{cc}$ contain $\frac{6.023\times {10}^{23}}{22400}\times 1.12\times {10}^{-7}$ molecules
$=3.01\times {10}^{12}$ molecules