1. Aim: How to convert from moles to volume and vice versa

2. 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.

3. STP
Volume of gas and temperature are usually measured at STP.
Standard temperature and pressure (STP) means temperature of 0oC and a pressure of kPa, or 1 atmosphere (atm).
At STP, 1 mole or 6.02 x representative particles of any gas occupies a volume of 22.4 L.

6. Calculating from moles of gas to volume of gas
Volume of gas = moles of gas x 𝐿 1 𝑚𝑜𝑙
Conversion Factor

7. Calculating the volume of a gas at STP
Determine the volume, in liters, of 0.60 mol SO2 gas at STP.
Identify known and unknown.
Known Unknown
1 mol = 22.4 L volume of 0.60 mol SO2
0.60 mol SO2

8. 2. Set up equation Volume = 0. 60 mol SO2 x 22
2. Set up equation Volume = 0.60 mol SO2 x 22.4 𝐿 1 𝑚𝑜𝑙 SO2 Volume = 13 L SO2

9. What is the volume of these gases at STP?
3.20 x 10-3 mol CO2
3.20 x 10-3 mol CO2 x 22.4 L / 1 mol = L CO2
b mol N2
3.70 mol N2 x 22.4 L / 1 mol = 82.9 L N2

10. Converting from volume of gas to moles of gas
Conversion Factor
Moles of gas = volume of gas x 1 𝑚𝑜𝑙 22.4 𝐿

11. Calculating number of moles of a gas at STP
How many moles of helium at STP will fit into a 39.6 L container?
Identify known and unknown.
Known Unknown
1 mol = 22.4 L # of moles
39.6 L

12. Moles = 1.77 mol He 2. Set up equation
Moles = 39.6 L He x 1 𝑚𝑜𝑙𝑒 𝐻𝑒 22.4 𝐿 𝐻𝑒
Moles = 1.77 mol He

13. How many moles of argon atoms are present in 11
How many moles of argon atoms are present in 11.2 L of argon gas at STP?
11.2 x 1mol / 22.4 L = moles

14. Calculating Molar Mass From Density
Reminder: Density= mass / volume
Density = molar mass / molar volume
Molar mass = density x molar volume
𝑔𝑟𝑎𝑚𝑠 𝑚𝑜𝑙𝑒 = 𝑔𝑟𝑎𝑚𝑠 𝑙𝑖𝑡𝑒𝑟𝑠 x 𝐿 1 𝑚𝑜𝑙𝑒
Molar volume
Molar Mass
density

15. Calculating molar mass of gas at STP
The desnity of a gaseous compound containing carbon ad oxygen is found to be g/L at STP. What is the molar mass of this compound.
List known and unknown.
Known Unkown
Density = g/L molar mass ?
1 mol = 22.4 L

16. Molar mass = 1.964 𝑔 1 𝐿 x 22.4 𝐿 1 𝑚𝑜𝑙 Molar mass = 44.0 g/mol
2. Set up equation.
Molar mass = 𝑔 1 𝐿 x 𝐿 1 𝑚𝑜𝑙
Molar mass = 44.0 g/mol

17. What is the density of krypton gas at STP
Find molar mass of krypton
molar mass = 83.8 g/mol
2. Set up Equation
Density (g/L) = molar mass/ molar volume
Density= 𝑔/𝑚𝑜𝑙 22.4 𝐿/𝑚𝑜𝑙 or Density= (83.8 g/1 mol) x (1 mol / 22.4 L)
Density of Kr = 3.74 g/L