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 in the flask, we can use the ideal gas law, which states:

$PV = nRT$

Where:

• P is the pressure in atm (0.201 atm)
• V is the volume in litres (1 L)
• n is the number of moles of the gas
• R is the ideal gas constant (0.0821 L·atm/(K·mol))
• T is the temperature in Kelvin (25°C + 273.15 = 298.15 K)

Rearranging the formula to find n:

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

Substituting the values:

$n = \frac{(0.201 \, \text{atm}) (1 \, \text{L})}{(0.0821 \, \text{L·atm/(K·mol)}) (298.15 \, \text{K})}$

Calculating this gives:

$n = \frac{0.201}{24.466} \approx 0.0082 \text{ moles}$