The Mole

The Mole: An expression of the quantity of matter. The quantity of matter is referred to a representative particles. One mole = x quantity (Avogadro’s #) The representative particles are: Atoms: One mole of atoms = 6.02 x atoms. Molecules: One mole of molecules = 6.02 x molecules. Ions: One mole of ions = 6.02 x ions Compounds: One mole of compound = 6.02 x compounds.

To determine: The mass in moles of an atom: Reference the periodic table. 1 mole of Na atoms = 6.02 x Na atoms= 23g (the atomic mass of Na) *the atomic mass of any element is the molar mass of that element.

PRACTICE How many moles of water are found in 95.1 grams of water?

How many atoms of water is that?

PRACTICE How many moles of N 2 would be in a 2.5 L container at STP?

PERCENT COMPOSITION

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

Percent Composition Refers to what part by mass of a compound does each element contribute. Formula: Mass of element X 100 = % Mass of compound

Sample Calcium Chloride : CaCl 2 Ca: 1 x 40 = 40 Cl: 2 x 35 = is the total mass % Comp Ca = 40 x 100 = % 110 % Comp Cl = 70 x 100 = 63.6 % %

EMPIRICAL FORMULAS

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 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 FORMULAS

Molecular Formula Actual number of elements expressed in a molecule. a. molecular formula = empirical formula x n b. Formula: molar mass of the molecule = n mass of the empirical formula n = the number of moles

Practice; Molecular formula

HYDRATES

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 Formula of A Hydrate Look Like? BaCl 2 2H 2 O FeSO 4 6H 2 O Na 2 CO 3 10H 2 O CuSO 4 5H 2 O

How are Names of Hydrates Written? BaCl 2 2H 2 O barium chloride dihydrate FeSO 4 6H 2 O iron(II) sulfate hexahydrate Na 2 CO 3 10H 2 O sodium carbonate decahydrate CuSO 4 5H 2 O copper(II) sulfate pentahydrate

What prefixes are used? 0.5hemi7hepta 1mono8octa 2di9nona 3tri10deca 4tetra11undeca 5penta12dodeca 6hexa13triskaideca

How can the water be 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 called after the water has been removed?

Hydrates 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 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?