The Mole: A Measurement of Matter

OBJECTIVES: Describe how Avogadro’s

number is related to a mole of any substance.

The Mole: A Measurement of Matter

OBJECTIVES: Calculate the mass of a mole of

any substance.

What is a Mole?

You can measure mass, or volume,or you can count pieces.We measure mass in grams.We measure volume in liters.

We count pieces in MOLES.

Moles (abbreviated: mol)

Defined as the number of carbon atoms in exactly 12 grams of carbon-12. 1 mole is 6.02 x 1023 particles.Treat it like a very large dozen6.02 x 1023 is called Avogadro’s number.

Representative particles

The smallest pieces of a substance. For a molecular compound: it is the

molecule. For an ionic compound: it is the

formula unit (ions). For an element: it is the atom.

Remember the 7 diatomic elements (made of molecules)

Types of questionsHow many oxygen atoms in the following? CaCO3

Al2(SO4)3

How many ions in the following? CaCl2 NaOH Al2(SO4)3

Types of questions

How many molecules of CO2 are there in 4.56 moles of CO2?

How many moles of water is 5.87 x 1022 molecules?How many atoms of carbon are there in 1.23 moles of C6H12O6?

How many moles is 7.78 x 1024 formula units of MgCl2?

Measuring Moles

Remember relative atomic mass? The amu was one twelfth the mass of a carbon-12 atom.Since the mole is the number of atoms in 12 grams of carbon-12,the decimal number on the periodic table is also the mass of 1 mole of those atoms in grams.

Gram Atomic Mass (gam)Equals the mass of 1 mole of an element in grams12.01 grams of C has the same number of pieces as 1.008 grams of H and 55.85 grams of iron.We can write this as

12.01 g C = 1 mole CWe can count things by weighing them.

Examples

How much would 2.34 moles of carbon weigh?How many moles of magnesium is 24.31 g of Mg?How many atoms of lithium is 1.00 g of Li?How much would 3.45 x 1022 atoms of U weigh?

What about compounds?

in 1 mole of H2O molecules there are two moles of H atoms and 1 mole of O atomsTo find the mass of one mole of a compound determine the moles of the elements

they have Find out how much they would weigh add them up

What about compounds?

What is the mass of one mole of CH4?

1 mole of C = 12.01 g4 mole of H x 1.01 g = 4.04g1 mole CH4 = 12.01 + 4.04 = 16.05g

The Gram Molecular Mass (gmm) of CH4 is 16.05g this is the mass of one mole of a

molecular compound.

Gram Formula Mass (gfm)

The mass of one mole of an ionic compound.Calculated the same way as gmm.What is the GFM of Fe2O3?

2 moles of Fe x 55.85 g = 111.70 g3 moles of O x 16.00 g = 48.00 gThe GFM = 111.70 g + 48.00 g =

159.70 g