The Mole

Chapter 10

Formula Mass:

Is what a single molecule “weighs” in amu’s (atomic mass units)

Revision:

So, 1 molecule of Water (H2O) weighs:2 x 1.01 (for H) + 1 x 16.00 (for O)= 18.02 amu’s

Example #2:What is the mass of 1 molecule of

Sugar(Sucrose)? (C6H12O6)

C: 6 x 12.01 =H: 12 x 1.01 =O: 6 x 16.00 =

Do other examples?a) CO2

b) (NH4)2CO3

The Mole:First, let’s look at names that reflect

numbers:

1 dozen =

1 baker’s dozen =

1 score =

1 gross =

Let’s now focus on a particular isotope – Carbon-12

1 Carbon-12 atom weighs ______________But this is an impractical measurement. We

want to work in the mass unit of grams.So, how many atoms of Carbon-12 would it

take to weigh 12.00 g.?

Amadeo Avogadro (Italian, 1776-1856) calculated the number to be 6.022 x 1023

and is also known as aSo now, the average atomic mass number also

represents how many grams that element would weigh if you had 1 mole of that substance.

So, 1 mole of Water weighs:H: 2 x 1.01 g/mole = 2.02 g/moleO: 1 x 16.00 g/mole = 16.00 g/mole

This # is known as the _____________(mass

of 1 mole) of Water.Examples. Calculate the Molar Mass of the

following:a.) SO2

b.) (NH4)3PO4

Mole to Mass & Mass to Mole ConversionsIf we are given the # moles of a substance and

we want to calculate how much it weighs (i.e. what’s its mass?), then we convert by using the _________________________!

E.g. What is the mass of 1.50 moles of Water?

1.50 mol. Of H2O x 18.02g of H2O = 27.03g of H2O

1 1 mol. of H2O

E.g.#2 What is the mass of 0.75 mol. Of Salt?

Now, going the other way.How many moles are in 100.g of CO2 ?

100.g of CO2 x 1 mol. of CO2 = _______________

1 44.01g of CO2

E.g.#2 How many moles are in a pound of Sugar?

Converting from moles to molecules & vicy versi

In these conversions, instead of using the _________________________, you use Avacado’s Avagadro’s Number. (NA)

Ex. How many molecules are in 1.50 moles of Water?(remember: 1 mole = 6.02 x 1023 )

1.50 mol. x 6.02 x 1023 molecules = ___________________1 1 mol.

Ex.2) How many moles in 2.107 x 1024 molecules of Salt?

2.107 x 1024 molecules x ____ = 3.50 moles

1 6.02 x 1023 molecules

Do these in-class egg samples:1.) How many molecules are in 0.02 moles

of Sugar?

2.) How many moles are in 3.01 x 1023 molecules of O2?

Let’s look at lotsof moleculesof Water.

Time to draw a MOLE diagramI know what you’re thinking! Now we can doMass to Molecules conversions & vicy versi.(Hint: it’s a 2 step Chain Method)Ex. How many molecules are in 12.0g (~½ oz) of

Water?

12.0g of H2O x _____________x________________________1 1 mol of H2O

= 4.00 x 1023 molecules of H2O

Ex. What does 9.03 x 1022 molecules of Vitamin C weigh?

(Vitamin C = C6H8O6)

The Volume occupied by 1 mole of a gas is the Molar Volume.

The Volume occupied by 1 mole of a gas @ STP is known as the Standard Molar Volume of a gas and is equal to 22.4 L.

@ STP

V = 22.4 L/mol. V = n x 22.4 L/mol.n

So 1 mole of any gas occupies 22.4L @ STP, but their masses may be different.

Standard Molar Volume

So 2 moles of a gas will occupy twice the space (Volume) of 1 mole.

e.g. 2H2 + O2 2H2O

(more examples: N2 + H2 NH3 ,…)

And remember:1 mole = 6.02 x 1023 molecules

(Diagram – New Mole Diagram)

Add that to the mole diagram…

Mass (Grams) Mole

Volume @STP

Molecules/ Atoms