Atomic mass the mass of an atom in atomic mass

units (amu)

Micro Worldatomic mass units

Macro Worldgrams

Discovery of the MOLEDiscovery of the MOLE

Amedeo Avogadro

•Avogadro’s number (NA)

6.02 × 1023

— is the number of particles in exactly one mole of a pure substance.

How do we measure an amount?How do we measure an amount?

mole (mol): amount of a substance that contains as many particles as there

are atoms in exactly 12.00 grams of 12C

1 mol = 6.02 x 1023

Avogadro’s number (NA)

The mole is the SI unit for the amount of substance.

1 dozen = 12

Relating Mass to Numbers of AtomsRelating Mass to Numbers of Atoms

•Unit: g/mol

•All molar masses should contain TWO decimal places

Molar mass is the sum of the atomic masses (in grams) in

a molecule.

SO2

1S 32.062O + 2 x 16.00 SO2 64.07 g/mol

1 molecule SO2 = 64.06 amu

1 mole SO2 = 64.06 g SO2

For any molecule

formula mass (amu) = molar mass (grams)

Calculate the molar mass for:

H2O C6H12O6

CO2 Mg(OH)2

Percent composition of an element in a compound =

n x molar mass of element

molar mass of compound x 100%

n = the number of moles of the element in 1 mole of the compound (IT IS THE SUBSCRIPT)

Steps to Calculating Percent Steps to Calculating Percent CompositionComposition

1. Calculate total mass

2. Set up ratio of part over whole

3. Multiply by 100.

4. Calculate!

All percentages should contain TWO decimal places

H: 2 x 1.01 = 2.02

O: 1 x 16.00 = 16.00

18.02 g/mol

2 x1.01 g/mol H 18.02 g/mol H2O

X 100 = 11.21 % H

16.00 g/mol O 18.02 g/mol H2O

X 100 = 88.79 % O

Find the percent composition of the elements in water (H2O).

H :

O :

Calculate Total Mass:

Al: 2 x 26.98 = 53.96

S: 3 x 32.07 = 96.21

O: 12 x 16.00 = 192.00

342.17 g/mol

Find the percent composition of the elements in Al2(SO4)3.

Find the percent composition of the elements in Al2(SO4)3. - continued.

53.96 g/mol Al 342.17 g/mol Al2(SO4)3

X 100 = 15.77 % Al

192.00 g/mol O 342.17 g/mol Al2(SO4)3

X 100 = 56.11 % O

96.21 g/mol S 342.17 g/mol Al2(SO4)3

X 100 = 28.12 % S

Al :

S :

O :

Define Empirical Formula:

A chemical formula that gives the simplest whole-number ratio of the elements in the formula.

Which of the following is an empirical formula? CO2 C2O4

Fe2Cl6 FeCl3

Define Molecular Formula:

A chemical formula that gives the actual number of the elements in the molecular compound.

For the following molecular formulas, write the empirical formula:

Molecular: Empirical: C2H4 C6H12O6

C9H21O6N3

Mole Mole ConversionsConversions

Converting between unitsConverting between units

The molar mass is used to convert the mass of a substance in grams to moles and the number of moles to grams of a substance .

11.2 g NaCl

Mass to Mole Conversions

1 mol NaCl58.44 g NaCl

0.192 mol NaCl

Na: 1 X 22.99 = 22.99Cl: 1 X 35.45 = 34.45 58.44 g/mol

÷ MOLAR MASS

3.2 mol Zn(NO3)2

Mole to Mass Conversions

189.53 g Zn(NO3)2

1 mol Zn(NO3)2

606 g Zn(NO3)2Zn: 1 X 65.39 = 65.39N: 2 X 14.07 = 28.14O: 6 X 16.00 = 96.00 189.53g/mol

x MOLAR MASS

Stoichiometry

MOLE

Mole RatioMole Ratio

mole ratio : a conversion factor that relates the amounts in moles of any two substances involved in a chemical reaction

ALWAYS NEED A BALANCED CHEMICAL EQUATION!!!

Example: 2Al2O3(l) → 4Al(s) + 3O2(g)

Mole Ratios:

2 mol Al2O3 2 mol Al2O3 4 mol Al

4 mol Al 3 mol O2 3 mol O2

Steps for completing stoichiometry:Steps for completing stoichiometry:

1. Write a balanced chemical equation.

2. Identify what is given.

3. Identify what is being found.

4. Write what is given.

5. Write the mole ratio.

6. Calculate unknown.

Sample problem: How many moles of HCl are needed to react with 2.3 moles Zn?

Eqn: __Zn + __HCl __ZnCl2 + __H2

Given:Unknown:

=

Mole to Mole How many moles of hydrogen are produced

when you start with 3.0 moles of NH3?

Given:Unknown:

__NH3 __N2 + __H2

3.0 mol NH3 3 mol H2

2 mol NH3

= 4.5 mol H2

DO NOWDO NOW

Balance the following equation:

___Fe + ___O2 ___Fe2O3

If you start with 3.23 moles of iron, how much iron(iii) oxide will be produced?

Limiting ReactantsLimiting Reactants limiting reactant : the reactant that limits

the amount of product that can form

excess reactant : the substance that is not used up completely in a reaction.

You are at home and ready to make some Betty Crocker Brownies to bring to chemistry class. You know the class is big so you need to make two batches of brownies. You gather all the supplies and this is what you have:

2 Packages of Brownie Mix

1 cup of water

1 cup of vegetable oil

3 eggs

Do you have enough supplies to make the brownies? What is limiting you? What is in excess?

Ingredients on Brownie Box:1 Package of Brownie Mix¼ cup of water½ cup of vegetable oil2 eggs

Percent Yield Percent Yield expected yield: maximum amount of

product that can be produced from a given amount of reactant.

actual yield: measured amount of that product obtained from a reaction.

percent yield: ratio of the actual yield to the expected yield, multiplied by 100.

actual yieldpercentage yield 100

theorectical yield

expected yield

Percent Yield ExamplePercent Yield Example

In an experiment, the scientist expected to produce 16.0 grams of silver in a reaction. The actual yield was 15.2 grams of silver. What is the % yield?

Cu + 2 AgNO3 Cu(NO3) 2 + 2 Ag