Chemistry Topic 3 The Mathematics of Formulas and

Chemistry Topic 3 The Mathematics of Formulas and Equations

• Mass of atom is based on the mass of a Carbon-12 atom • Formula Mass – sum of the atomic masses of all the atoms present. • Gram Formula Mass – formula mass expressed in grams instead of atomic mass units. • Use 35. 5 for Cl

Find the Gram Formula Masses • • Na O 2 Na. Cl HBr Na. OH Mg 3 N 2 Al 2(SO 4)3

• Percent Composition – composition as a percentage of each element compared to the total mass of the compound.

Find the Percent Composition • • Na O 2 Na. Cl HBr Na. OH Mg 3 N 2 Al 2(SO 4)3

• Hydrates – crystals that contain water. • Anhydrous – substances without water • To calculate % water, treat the water molecule as a single unit.

Calculate % Water • Cu. SO 4∙ 5 H 2 O

11/6 Chemistry Aim: What calculations can we perform with formulas? Obj: SWBAT calculate moles, find molecular formulas, and set up mole ratios Do Now: What is the formula mass of Na. OH? Homework: Worksheet

Moles • Mole = number of atoms of carbon present in 12. 000 g of C-12 • Avogadro’s number = 6. 022 x 1023 – Number of particles in a mole of a substance

• Moles = grams / gram formula mass • Grams = moles x gram formula mass

• What is the mass in grams of a 8. 4 mole sample of iron? • Convert 0. 45 g of sodium hydroxide, Na. OH to moles. • How many moles of potassium nitrate, KNO 3 are present in a sample with a mass of 85. 2 g. • What is the mass in grams of 0. 94 moles of sodium bicarbonate, Na. HCO 3?

Finding Molecular Formulas from Empirical Formulas • Find the formula mass of the empirical formula • Divide mass of compound by the mass of the empirical formula. • Multiply your empirical by that answer.

• A compound has an empirical formula of CH 2 and a molecular mass of 56 amu. What is its molecular formula? • A compound has an empirical formula of CH and a molecular mass of 78 amu. What is the molecular formula?

Mole Relations in Balanced Equations • Set up ratios • Also works for volumes of gases