One litre of air at atmospheric pressure and 25°C is held in a flask - VCE - SSCE Chemistry - Question 17 - 2005 - Paper 1

To find the concentration of oxygen, we first need to use the ideal gas law, which is given by the equation:

$PV = nRT$

Where:

• $P$ is the pressure of the gas (in atm),
• $V$ is the volume of the gas (in liters),
• $n$ is the number of moles of the gas,
• $R$ is the ideal gas constant (0.0821 L·atm/(K·mol)), and
• $T$ is the temperature (in Kelvin).

1. Convert the temperature from Celsius to Kelvin:
   $T = 25 + 273.15 = 298.15 ext{ K}$
2. Rearranging for the number of moles:
   $n = \frac{PV}{RT}$
3. Substitute in the known values:
   $n = \frac{(0.201 ext{ atm})(1 ext{ L})}{(0.0821 ext{ L·atm/(K·mol)})(298.15 ext{ K})}$
   $n \approx 0.0082 ext{ mol}$