SAT Subject Test Chemistry,10 edition

Substituting    into    the ideal   gas equation:

FURTHER USES OF THE IDEAL GAS LAW

In addition to standard calculations to determine the pressure, volume, or temperature of a gas, the
ideal gas law may be used to determine the density and molar mass of a gas.

BASIC CONCEPT

density =   mass/volume

Calculating Density

Density is defined as the mass per unit volume of a substance and, for gases, is usually expressed in
units of g/L. By rearrangement, the ideal gas equation can be used to calculate the density of a gas.

PV  =   nRT

n, the number of moles, is also equal to m/M where m = total mass (in g) and M = molar mass (in
g/mol).

Another way to find the density of a gas is to start with the volume of a mole of gas at STP, 22.4 L,
calculate the effect of pressure and temperature on the volume, and finally calculate the density by