UNIT 6: CHEMICAL QUANTITIES

Chapter 10: Mole and Volume Relationships

The Mole and Volume Relationships

We know that the mass for one mole for different substances will vary because of the molar mass

How about volume?

The Mole and Volume Relationships

The volume for a substance will vary because each substance has a different number of atoms in them and each atom is a different size This is true for liquids and solids

A gas occupies the same amount of space regardless of the size of the atom or molecule

The Mole and Volume Relationships

Avogadro's Hypothesis Equal volumes of gases at the same

temperature and pressure contain equal numbers of particles.

STP Standard Temperature and Pressure

Temperature is equal to 0˚ C Pressure is equal to 101.3 kPa or 1 atm

At STP, 1 mol or 6.02 x 1023 representative particles, of any gas occupies a volume of 22.4 L. 1 mole = 6.02 X 1023 = 22.4 L

The Mole and Volume Relationship

Calculating Volume at STPVolume of gas = Moles of gas X

Practice Determine the volume in liters of

0.60 mol SO2 gas at STP

22. 4 L 1 mol

0.60 mol SO2 22. 4 L SO2 = 13 L SO3

1 mol SO2

Volume and Molar Mass Relationship

Using Density to find the molar mass of a gas Cannot find the mass of a gas by weighing

it Remember Density = Mass / Volume or

Grams / Liters Molar mass = density at STP × Molar

volume at STP

= ×

Grams

mole

Grams

Liter

22.4 Liters1 Mole

Example The density of a gaseous compound

containing carbon and oxygen is found to be 1.964 g/L at STP. What is the molar mass of the compound?

1.964 g 22. 4 L = 44.0 g/mol 1 L 1 mol

Volume and Molar Mass Relationship

Mixed Mole Problems

Use the map to be able to convert g atoms,

molecules liters, liters grams, or any other

combination.

ALWAYS convert to moles first!

Example What is the volume, in liters, of 835 g SO3

at STP? Find out where on the map you are

starting (given value) Convert to moles Then use the conversion to get where

you need to end on the map. Molar Mass SO3 = 80.1 g/mol

Volume and Molar Mass Relationship

835 g 1 mol 22.4 L = 234 L SO3

80.1 g 1 mol

Example What is the mass, in grams, of a molecule

of aspirin (C9H8O4)? Molar Mass C9H8O4 = 180.0 g/mol

Volume and Molar Mass Relationship

1 molec 1 mol 180.0 g = 2.99×10-22 g aspirin

6.02×1023 molec 1 mol