A sample of oxygen has a volume of 205cm³ when its temperature is 22.0°C and its pressure is 30.8 kPa.

What volume will the gas occupy at STP?

Use the ideal gas equation:

PV = nRT
Hence, 'nR' is a constant term
=> (PV/T) = constant

=> (PV/T)1 = (PV/T)2

Put in the given values on the left hand side and the STP conditions on the right. Remember to take temperature in Kelvin!

To find the volume of the gas at STP (Standard Temperature and Pressure), we need to use the Combined Gas Law. The Combined Gas Law formula is:

(P₁ * V₁) / (T₁) = (P₂ * V₂) / (T₂)

Where:
P₁ = Initial Pressure (30.8 kPa)
V₁ = Initial volume (205 cm³)
T₁ = Initial temperature in Kelvin (22.0 + 273.15 = 295.15 K)
P₂ = Final Pressure (STP pressure = 101.3 kPa)
V₂ = Final volume (unknown)
T₂ = Final temperature in Kelvin (STP temperature = 273.15 K)

To find the final volume (V₂), we rearrange the formula:

V₂ = (P₂ * V₁ * T₂) / (T₁ * P₁)

Now, we can substitute the values:

V₂ = (101.3 kPa * 205 cm³ * 273.15 K) / (295.15 K * 30.8 kPa)

Calculating this expression:

V₂ ≈ 187.4 cm³

Therefore, at STP, the oxygen gas will occupy approximately 187.4 cm³ volume.