Question

A sample of oxygen gas occupies 500.0 mL at -185°C and 75.0 cmHg. Calculate the temperature in °C if the gas has a volume of 221.0 mL at a 55.0 cmHg.

Answer 1

PV/T remains constant, so

(75.0)(500)/(-185+271) = (55)(221.0)/T

T = 28°K

Note that we don't really have to convert to L and Pa, because the same conversion factors would be applied to both sides of the equation. The only wrinkle is the °C-°K conversion, because that is additive, not multiplicative.

Answer 2

This answer is not correct

Answer 3

Steve gave you the combined gas law, but it seems that you were confused. The gas law is as followed:

P1V1/T1=P2V2/T2

Where

P1=75.0 cmHg
V1=500.0 mL
T1=273K +(-185ºC)=88K
P2=55.0 cmHg
V2=221.0mL
and
T2=?

Solve for T2:

T2=[T1*(P2V2)]/P1V1

T2=[88K*(55.0 cmHg*221.0mL)/(75.0 cmHg*500.0 mL)

T2=28.6 K

Convert Kelvin to Celsius:

K=273K +C

K-273=C

28.6-273=-244 º C <== Three significant figures