Aim: How to convert
from moles to volume
and vice versa
Avogardo’s Hypothesis
 Avogadro's
hypothesis says that the same
volume of gas contains the same
number of particles. It
does not matter what gas you have,
they all contain the same number of particles
provided that they are at
the same temperature and pressure.
STP
 Volume of gas and temperature are
usually measured at STP.
 Standard temperature and pressure (STP)
means temperature of 0oC and a pressure
of 101.3 kPa, or 1 atmosphere (atm).
 At STP, 1 mole or 6.02 x 1023
representative particles of any gas
occupies a volume of 22.4 L.
Calculating from moles of gas to volume
of gas
Conversion Factor
Volume of gas = moles of gas x
22.4 𝐿
1 𝑚𝑜𝑙
Calculating the volume of a gas at STP
 Determine
at STP.
1. Identify
the volume, in liters, of 0.60 mol SO2 gas
known and unknown.
Known
1 mol = 22.4 L
0.60 mol SO2
Unknown
volume of 0.60 mol SO2
2. Set up equation
22.4 𝐿
Volume = 0.60 mol SO2 x
SO2
1 𝑚𝑜𝑙
Volume = 13 L SO2
What is the volume of these gases at
STP?
a. 3.20
x 10-3 mol CO2
3.20 x 10-3 mol CO2 x 22.4 L / 1 mol = 0.0717 L CO2
b. 3.70 mol N2
3.70 mol N2 x 22.4 L / 1 mol = 82.9 L N2
Converting from volume of gas to moles
of gas
Conversion Factor
1 𝑚𝑜𝑙
Moles of gas = volume of gas x
22.4 𝐿
Calculating number of moles of a gas at
STP
 How
many moles of helium at STP will fit
into a 39.6 L container?
1.
Identify known and unknown.
Known
Unknown
1 mol = 22.4 L
# of moles
39.6 L
2. Set up equation
1 𝑚𝑜𝑙𝑒 𝐻𝑒
Moles = 39.6 L He x
22.4 𝐿 𝐻𝑒
Moles = 1.77 mol He
How many moles of argon atoms are
present in 11.2 L of argon gas at STP?
11.2 x 1mol / 22.4 L = 0.500 moles
Calculating Molar Mass From Density

Reminder: Density= mass / volume

Density = molar mass / molar volume

Molar mass = density x molar volume
𝑔𝑟𝑎𝑚𝑠 𝑔𝑟𝑎𝑚𝑠 22.4 𝐿
=
x
𝑚𝑜𝑙𝑒
𝑙𝑖𝑡𝑒𝑟𝑠 1 𝑚𝑜𝑙𝑒
Molar Mass
density
Molar
volume
Calculating molar mass of gas at STP
 The
desnity of a gaseous compound containing carbon
ad oxygen is found to be 1.964 g/L at STP. What is the
molar mass of this compound.
1. List
known and unknown.
Known
Density = 1.964 g/L
1 mol = 22.4 L
Unkown
molar mass ?
2
. Set up equation.
1.964 𝑔
Molar mass =
1𝐿
x
22.4 𝐿
1 𝑚𝑜𝑙
Molar mass = 44.0 g/mol
What is the density of krypton gas at
STP
1. Find
molar mass of krypton
molar mass = 83.8 g/mol
2. Set up Equation
Density (g/L) = molar mass/ molar volume
83.8 𝑔/𝑚𝑜𝑙
Density=
or Density= (83.8 g/1 mol) x (1 mol / 22.4 L)
22.4 𝐿/𝑚𝑜𝑙
Density of Kr = 3.74 g/L