Compound Stoichiometry

The Mole Unit for dealing with the number of atoms, ions, or molecules in a common sized sample Relationship between Moles and Atoms, Molecules, and Ions (formula units) Avogadro’s number 6.02 x How many formula units are in one mole 1 mol 12 C atoms = 6.02 x C atoms 1 mol H 2 O molecules = 6.02 x H 2 O molecules 1 mol NO 3 - ions = 6.02 x NO 3 - ions

Molar Mass (g/mol) Molar mass is the mass of one mole of a substance Think of mole as a number, like dozen or pair Calculate by using the average atomic masses and the subscripts in the chemical formula Examples Calculate the molar mass of: Sodium chloride Copper (II) hydroxide Phosphorous trichloride

Percent Composition or Mass Percent Mass Percent = mass of the part mass of the whole Examples: Calculate the mass percent of the bolded element. Sodium nitrate Magnesium phosphate X 100

% Composition Continued Find the % comp of Fluorine in Calcium Fluoride 1. (Average Atomic mass of Fluorine) X (# of atoms) 2. Divide that by the Molar Mass for Calcium Fluoride 3. Multiply the answer by The unit is %

Relationship between moles and mass Use molar mass (g/mol) like a conversion factor- Just like we did with the metric system! 1 mol C = g 1 mol H 2 O = g

Problems Calculate the number of moles of glucose in g of glucose g C 6 H 12 O 6 X 1 mol C 6 H 12 O 6 = g C 6 H 12 O 6 Calculate the mass in grams of moles of sodium phosphate. Calculate the number of glucose molecules in moles of glucose (C 6 H 12 O 6 ) How many glucose molecules are in a 5.0 g sample of glucose?

The Mole Unit for dealing with the number of atoms, ions, or molecules in a common sized sample Relationship between Moles and Atoms, Molecules, and Ions (formula units) Avogadro’s number 6.02 x How many formula units are in one mole 1 mol 12 C atoms = 6.02 x C atoms 1 mol H 2 O molecules = 6.02 x H 2 O molecules 1 mol NO 3 - ions = 6.02 x NO 3 - ions

Problems How many glucose molecules are in 5.23 g? How many oxygen atoms are in this sample? How many nitric acid molecules are in 4.20 g? How many silver atoms are in 4.50 g? How many moles of sodium carbonate are in 508 g? How many oxygen atoms are in 0.25 mol of calcium nitrate?

Activity A Day in the Life of Avogadro

Bell Ringer Prepare for Quiz Molar Mass % Composition Converting from grams to mole Converting from mole to formula unit Converting molecule to atom

Quiz 1. Find the Molar Mass of Potassium Phosphate 2. What is the % Composition of Phosphorous in Potassium Phosphate? 3. If I have 15.0g of Potassium Phosphate, how many moles will I have? 4. How many molecules of Potassium Phosphate will be in 15.0g of Potassium Phosphate? 5. How many atoms of Potassium will be in the 15.0 g of Potassium Phosphate?

Molar Volume Number of liters of any gas equal to one mole of that gas at STP (standard temp and pressure) 1 mol (of any gas) = 22.4 L (of that gas) 1 mol Ne = 22.4 L Ne 1 mol O 2 = 22.4 L O 2 1 mol H 2 = 22.4 L H 2

Empirical Formulas Lowest whole number ratio (Simplest formula) Mole ratio Use mass percent to determine formula

Solving Empirical Formula Problems Steps 1.Assume 100 g sample- unless given # of grams 2.Convert mass to moles for each element 3.Divide by lowest mole value to get whole number ratio oRounding rules o.0,.1 or.2 (Leave number the same) o.8 or.9 (Round up) oAll others (.5) multiply to get whole number- usually by 2 4.Use whole numbers as subscripts and write formula

Examples 75% carbon, 25% hydrogen 52.7% potassium, 47.3% chlorine

Molecular Formula “True” Formula More complex Based on empirical Sometimes equals empirical

Solving Molecular Formula Problems Steps 1.Find Empirical formula (unless already given) 2.Compare molar mass of empirical formula with the true molar mass (given in problem) 3.Multiply to get subscripts

Examples The empirical formula of a compound is NO 2. Its molecular mass is 92 g/mol. What is its molecular formula? A compound is found to be 40.0% carbon, 6.7% hydrogen, and 53.5% oxygen. Its molecular mass is 60.g/mol. What is its molecular formula?