Chapter 11 Mathematics & Chemical Formulas

Unit 6 – The Mole

Atoms are too small/light

Atoms are too small and too light to count or mass as individuals– One Carbon-12 atom = 1.99 x 10-23 grams

We use this as the basis for atomic mass units. 1 Carbon atom is 12 amu.

– 6 protons + 6 neutrons = 12 “things” that make up the mass of a carbon atom

One amu = 1/12 of a carbon atom

Atomic Mass & Formula Mass

Atomic mass - the mass of 1 mole of atoms (also known as “molar mass”)

Formula mass - the masses of all the atoms in an ionic compound. Ex: CaCl2

Molecular Mass – the masses of all of the atoms in a molecular compound. Ex: CH4

Formula Weight (FW)

So, the formula weight of calcium chloride, CaCl2, would be

Ca: 1(40.1 amu)

+ Cl: 2(35.5 amu)

111.1 amu

To convert to molar mass, change amus to g/mol. 1 amu = 1 g/mol

Molecular Weight (MW)

For the molecule methane, CH4, the molecular weight would be

C: 1(12.0 amu)

16.0 amu+ H: 4(1.0 amu)

The molar mass of methane would be 16.0 g/mol

1 mole - different physical states

Moles provide a bridge from the molecular scale to the real-world scale.

Examples of Molar Mass

List the molar masses of the following:– Zn

– CuSO4

– NaCl

– H2O

– Al2(SO4)3

The Mole – a word that means a #

Other words that mean #s: One dozen =

12

One gross = 144

One score = 20

One ream = 500

One MOLE = 6.02 x 1023

602000000000000000000000

Where does Avogadro’s Number come from?

A formula:

M = NAmC

The mass of 1 carbon-12 atom is 1.99 x 10-23 g

Avogadro’s Number

Avogadro’s Number - 6.02 x 1023 particles in 1 mole 1 mole of 12C has a mass of 12 g.

Mole Conversions

Moles tell you how many atoms you have, AND how much mass in grams you have.

We use moles to convert from atoms and grams.

Mole Conversion Factors

There are 4 possible conversion factors for mole conversions:– Show your work -use a conversion factor every time

Mole Diagram – Conversion Factors

Using your calculator

To Enter 6.02 x 1023 into your calculator, use the EE button, so it would appear as 6.02E23. Practice with the two following examples

Examples:

If you have 4.25 x 1022 atoms of Al, how many moles do you have?

If you have 0.37 moles of Al, how many atoms do you have?

Mole Examples (lol)

If you have 8.64g of Mg, how many moles do you have?

If you have 1.23 moles of Phosphorous, how many grams do you have?

Mole Relationships

One mole of:– atoms– ions– molecules

contains Avogadro’s number of those particles.

One mole of:– molecules or formula units

contains Avogadro’s number times the number of atoms or ions of each element in the compound.