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Unit 5 – The Mole

What is the Mole?

Molar Mass

How do we measure items?

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.

What is the mole?

We’re not talking about this kind of mole!

A. What is the Mole?

A counting number (like a dozen)

Avogadro’s number

1 mol = 6.02 1023 items

A large amount!!!!

Similar Words for an amount Pair: 1 pair of shoelaces

= 2 shoelaces Dozen: 1 dozen oranges

= 12 oranges Gross: 1 gross of pencils

= 144 pencils Ream: 1 ream of paper

= 500 sheets of paper

Practice… If I have 1 mole of marshmallows, how

many do I have?

If I have 2 moles of jelly beans, how many do I have?

If I have 6.02 x 1023 pennies, how many do I have?

6.02 X 1023 Marshmallows

2 moles 6.02 x 1023 jelly beans

1 mole

= 1.2 x 1024 jelly beans

1 mole of pennies

1 mole of hockey pucks would equal the mass of the moon!

A. What is the Mole?

1 mole of pennies would cover the Earth 1/4 mile deep!

1 mole of basketballs would fill a bag the size of the earth!

Why do we need the mole?Why do we need the mole?

The mole is used as a mass The mole is used as a mass comparison for any element in the comparison for any element in the periodic table.periodic table.

We can compare the mass in grams We can compare the mass in grams of any two elements of any two elements only if they only if they contain the same number of atoms.contain the same number of atoms.

Remember 1 dozen Golf balls vs. 1 dozen marblesRemember 1 dozen Golf balls vs. 1 dozen marbles

Why 6.02 x 1023 ?

Where did this number come from?

This is the number of atoms in exactly 12.0 grams of Carbon-12.

This is the standard for the mole!

It is a very large number, because atoms are so small!

Atomic MassAtomic Mass = the mass of = the mass of one atom of any element in one atom of any element in atomic mass units (amu).atomic mass units (amu).

Molar MassMolar Mass – the mass in – the mass in grams of one mole of atoms grams of one mole of atoms or molecules.or molecules.

1 Sodium atom weighs – 23 amu’s1 Sodium atom weighs – 23 amu’s 1 mole of Na atoms weighs – 1 mole of Na atoms weighs –

23 23 gramsgrams

Molar Mass Examples

carbon

sulfur

Copper

12.01 g/mol

32.07 g/mol

63.55 g/mol

Molar Mass Molar mass is the generic term

for the mass of one mole of any substance

(expressed in grams/mol) The same as: 1) Gram Molecular Mass (for molecules)

2) Gram Formula Mass (ionic compounds)

3) Gram Atomic Mass (for elements) molar mass is just a much broader

term than these other specific masses

Calculating Molar Mass for Compounds

Calculate the formula mass of magnesium carbonate, MgCO3.

24.3 g + 12 g + 3 x (16.00 g) = 84.3 g

Thus, 84.3 grams is the formula mass for MgCO3.

Molar mass is determined by the adding the Molar mass is determined by the adding the weights of all the atoms in a compound.weights of all the atoms in a compound.

Compound Molar Mass Examples

water

sodium chloride

H2O

2(1.01) + 16.00 = 18.02 g/mol

NaCl 22.99 + 35.45 = 58.44 g/mol

Molar Mass Examples

sodium bicarbonate

sucrose

NaHCO3

22.99 + 1.01 + 12.01 + 3(16.00)

= 84.01 g/mol

C12H22O11

12(12.01) + 22(1.01) + 11(16.00)

= 342.34 g/mol