Question

An open flask sitting in a lab fridge looks empty, but it is filled with a mixture of gases called air. Calculate the number of molecules of gas the flask contains if the flask volume is 2.50 L , and the air is at standard temperature and pressure (STP).

Answer 1

Answer: The number of molecules of gas the flask contains is $0.674\times 10^{23}$

Explanation:

According to ideal gas equation:

$PV=nRT$

P = pressure of gas = 1 atm   (STP)

V = Volume of gas = 2.50 L

n = number of moles  = ?

R = gas constant =$0.0821Latm/Kmol$

T =temperature = 273K (STP)

$n=\frac{PV}{RT}$

$n=\frac{1atm\times 2.50L}{0.0821 L atm/K mol\times 273K}=0.112moles$

According to Avogadro's law:

1 mole of gas at STP contains =$6.023\times 10^{23}$ molecules

Thus 0.112moles of gas at STP contains = $\frac{6.023\times 10^{23}}{1}\times 0.112=0.674\times 10^{23}$ molecules

The number of molecules of gas the flask contains is $0.674\times 10^{23}$