Moles The Mole 1 dozen 12 1 mole

Moles

The Mole • 1 dozen = 12 • 1 mole = 6. 02 x 1023 • The mass of 1 mole of an element is the mass on the periodic table ▫ 1 mole of Hydrogen = 1 g of Hydrogen ▫ 1 mole of Helium = 4 g of Helium Stoichiometry

Stoichiometry

Molar Mass • Molar mass is the mass of 1 mole of a substance • Units: g/mol ▫ The molar mass of an element is the mass number for the element that we find on the periodic table ▫ The molar mass of a compound is the mass of the elements in that compound added together. We have special terms for the molar mass of a compound. Stoichiometry

Molar Mass • Calculate the molar mass of Na. Cl: Na: 1 x 23 = 58 g/mol Cl: 1 x 35 = 35 } • Calculate the molar mass of Na(NO 3)2: Na: 1 x 23 = 23 N: 2 x 14 = 28 = 147 g/mol O: 6 x 16 = 96 } Stoichiometry

Conversion Review • What is a ratio? ▫ A comparison of two things which are equal to one another • Remember how we use ratios to perform metric conversions: ▫ How many centimeters in 5 meters? ▫ 5 m x 100 cm = 500 cm 1 m Stoichiometry

Conversions • We use molar mass as a ratio for conversions ▫ Molar mass = g/mol • We use Avogadro’s number as a ratio for conversions ▫ 6. 02 x 1023 atoms, molecules / 1 mol Stoichiometry

Conversions • To convert from grams to moles: ▫ 12 g Helium x 1 mole Helium = 3 moles Helium 4 g Helium • To convert from moles to atoms: ▫ 3 moles He x 6. 02 x 1023 atoms He = 1. 81 x 1023 atoms He 1 mole He Stoichiometry

Conversion Review • Remember when converting between two units with prefixes we used two ratios. • We always go through the base unit: ▫ How many kilometers in 500 centimeters? 500 cm x 1 meter x 1 kilometer = 0. 005 km 100 cm 1000 m Stoichiometry

Conversions • To convert from grams to atoms we use two ratios • Just like we go through the base unit for twostep metric conversions, we go through the mole for two-step mole conversions Stoichiometry

conversions • To convert from grams to atoms: 16 g He x 1 mole He x 6. 02 x 1023 atoms He = 2. 41 x 1023 4 g He 1 mole He atoms He • To convert from atoms to grams: 3. 5 x 1023 x 1 mole He x 4 g He = 2. 33 g atoms He 6. 02 x 1023 atoms He 1 mole He Stoichiometry