The MoleThe Mole

The Mole: An expression of the quantity of The Mole: An expression of the quantity of matter. The quantity of matter is matter. The quantity of matter is referred to a representative particles.referred to a representative particles.

One mole = 6.023 x 1023 quantity (Avogadro’s #)

The representative particles are:

Atoms: One mole of atoms = 6.02 x 1023 atoms.

Molecules: One mole of molecules = 6.02 x 1023 molecules.

Ions: One mole of ions = 6.02 x 1023 ions

Compounds: One mole of compound = 6.02 x 1023 compounds.

To determine:To determine:The mass in moles of an atom:The mass in moles of an atom:Reference the periodic table.

1 mole of Na atoms = 6.02 x 1023 Na atoms= 23g (the atomic mass of Na)

*the atomic mass of any element is the molar mass of that element.

PRACTICEHow many moles of water are found in 95.1 grams of water?

How many atoms of water is that?

PRACTICEHow many moles of N2 would be in a 2.5 L container at STP?

PERCENT COMPOSITIONPERCENT COMPOSITION

What is the percent of fat grams in a quarter pounder with cheese? What is the percent of sugar?

Percent Composition Percent Composition

Refers to what part by mass of a compound does each element contribute.

Formula: Mass of element X 100 = % Mass of compound

SampleSample

Calcium Chloride : CaCl2Ca: 1 x 40 = 40Cl: 2 x 35 = 70

110 is the total mass

% Comp Ca = 40 x 100 = 36.36 %110

% Comp Cl = 70 x 100 = 63.6 % 110 100 %

EMPIRICAL FORMULAS

Empirical Formula Empirical Formula

Expression of the smallest whole number ratio of elements in a molecule.

a. May or may not be the same as the molecular formula.

b. Total percentage of any compound is 100%.

Empirical FormulaEmpirical Formula 1. Convert % to mass (total percentage is 100%).

2. Convert mass to moles via the molar mass.

3. Divide the moles by the smallest mole value to determine the mole ratio within the compound.

4. If not a whole number, multiply the mole ratio from #3 by the smallest whole #.

5. The answers are the subscript in the empirical formula.

MOLECULAR FORMULASMOLECULAR FORMULAS

Molecular Formula Molecular Formula Actual number of elements expressed in a

molecule.

a. molecular formula = empirical formula x n

b. Formula:molar mass of the molecule = nmass of the empirical formula

n = the number of moles

Practice; Molecular formulaPractice; Molecular formula

HYDRATESHYDRATES

What is a Hydrate?What is a Hydrate?

Any salt that has water chemically bonded to the ions in the crystal structure is a hydrate or hydrated crystal.◦Copper(II) sulfate is a

hydrate.◦Hydrated copper(II) sulfate

is deep blue in color.

What does the Chemical What does the Chemical Formula of A Hydrate Look Formula of A Hydrate Look Like?Like?

BaCl2•2H2O

FeSO4•6H2O

Na2CO3•10H2O

CuSO4•5H2O

How are Names of Hydrates How are Names of Hydrates Written?Written?

• BaCl2•2H2O• barium chloride dihydrate

• FeSO4•6H2O• iron(II) sulfate hexahydrate

• Na2CO3•10H2O• sodium carbonate decahydrate

• CuSO4•5H2O• copper(II) sulfate pentahydrate

What prefixes are used?What prefixes are used?

0.5 hemi 7 hepta

1 mono 8 octa

2 di 9 nona

3 tri 10 deca

4 tetra 11 undeca

5 penta 12 dodeca

6 hexa 13 triskaideca

How can the water be How can the water be removed?removed?

Heat the crystal. The water is loosely bound, and will come away as water vapor.

Put the crystal in contact with or near a desiccant, maybe in a desiccator.

Anhydride (noun)◦The light blue powder is the anhydride.

Anhydrous (adjective)◦Anhydrous copper(II) sulfate is left in the test

tube after heating.

What is the compound What is the compound called after the water has called after the water has been removed?been removed?

HydratesHydrates

Compounds with water molecules attached.a. Review the prefixes. P: 351 IN BOOK

b. The mass of the water is included in the mass of the total molecule.

c. Calculation of % composition, empirical formula and molecular formula is the same with hydrate. EXCEPT the mass of the water molecules are included.

PRACTICE: HYDRATE FORMULA

A 15.67 g sample of a hydrate of magnesium carbonate was heated, without decomposing the carbonate, to drive off the water. The mass was reduced to 7.58 g. What is the formula of the hydrate?