Mass, the Mole, and Avogadro’s Number (Molar Mass)

The Mass of a Mole C-12 Basis Atomic masses are based on the mass of a C-12 atom. Molar masses are based on the mass of a mole of C-12 atoms.

Molar Mass (MM) Definition –The mass in grams of 1 mole of any substance. – Has the units g / mol Units

The molar mass (MM) of any element is numerically equal to its atomic mass. Molar Mass of Elements 20 Ca 40.08a Ex: Molar mass of Ca Ex: Molar mass of Cl 17 Cl Cl

Ex: Molar mass of CaCl 2 Avg. Atomic mass of Calcium = 40.08g Avg. Atomic mass of Chlorine = 35.45g Molar Mass of Compounds The molar mass (MM) of a compound is determined the same way, except now you add up all the atomic masses for the molecule (or compound) 20 Ca 40.08a 17 Cl Cl Molar Mass of calcium chloride = g/mol Ca + (2 X 35.45) g/mol Cl g/mol CaCl2

Molar Mass Practice Problem Calculate the Molar Mass of calcium phosphate Ca 3 (PO 4 ) 2 Formula = Masses of elements: Molar Mass = = Ca = g P = g O = g 3 ( g) + 2 ( g) + 8 ( g) g Ca 3 (PO 4 ) 2 / mole

Find the molar mass of: – Copper – Sulfuric acid – Xenon tetrafluoride – Hypochlorous acid – Oxygen Molar Mass Practice Problems g / mol g / mol g / mol g / mol g / mol

Flowchart Representative Particles Moles Mass (grams) 1 mol______ 6.02 X particles 1 mol

Flowchart Representative Particles Moles Mass (grams) 1 mol______ 6.02 X particles 1 mol molar mass 1 mol _____1 mol_____ molar mass

Mole  Mass # of moles x # of grams = mass 1 mol mol Cr x g Cr = 2.34 g Cr 1 mol Cr Example: Calculate the mass in grams of moles of chromium.

Calculate the mass of moles of calcium. Mole  Mass Practice Problems Determine the mass of moles of tin (II) sulfate.

Calculate the mass of moles of calcium. Mass of Ca = mol Ca x grams Ca 1 mol Ca Mass of Ca = mol Ca x grams Ca 1 mol Ca = 25.0 g Ca Mole  Mass Practice Problems

Determine the mass of moles of tin (II) sulfate. Mass of SnSO 4 = mol SnSO 4 x grams SnSO 4 1 mol SnSO 4 Mass of SnSO 4 = mol SnSO 4 x grams SnSO 4 1 mol SnSO 4 = 40.2 g SnSO 4 Mole  Mass Practice Problems

Mass  Mole Mass x ____1 mole____ = # of moles # of grams Example: How many moles of calcium are in 525 grams of calcium? 525 g Ca x 1 mol Ca = 13.1 mol Ca g Ca

A roll of copper wire has a mass of 848 g. How many moles of copper are in the roll? Mass  Mole Practice Problems At 4.0°C, water has a density of g/ml. How many moles of water are in kg of water?

A roll of copper wire has a mass of 848 g. How many moles of copper are in the roll? Mass  Mole Practice Problems Mass Cu x ____1 mole_Cu___ = # of moles Cu # of grams Cu 848 g Cu x ____1 mole_Cu___ = 13.3 moles Cu g Cu

Mass  Mole Practice Problems At 4.0°C, water has a density of g/ml. How many moles of water are in kg of water? Mass H 2 O x ____1 mole_ H 2 O ___ = # of moles H 2 O # of grams H 2 O x 10 3 g H 2 O x ____1 mole_ H 2 O __ = moles H 2 O g H 2 O

Mass  Atoms Mass x ____1 mole____ x 6.02 x atoms = # of atoms # of grams 1 mole Example: How many atoms of gold are in a pure gold nugget having a mass of 25.0 grams? 25.0 g Au x 1 mol Au x 6.02 x atoms Au = 7.65 x atoms Au g Au 1 mol Au

Mass  Atoms Practice Problems Mass x ____1 mole____ x 6.02 x atoms = # of atoms # of grams 1 mole Practice: How many atoms of lead are in 4.77 g of lead ? How many molecules of benzene are in 17.2 g of benzene (C 6 H 6 ) ?

Mass  Atoms Practice Problems Mass x ____1 mole____ x 6.02 x atoms = # of atoms # of grams 1 mole How many molecules of benzene are in 17.2 g of benzene (C6H6) ? 17.2 g C 6 H 6 x 1 mol C 6 H 6 x 6.02 x molec C 6 H 6 = 1.33 x molec g C 6 H 6 1 mol C 6 H 6 C 6 H 6 How many atoms of lead are in 4.77 g of lead ? 4.77 g Pb x 1 mol Pb x 6.02 x atoms Pb = 1.38 x atoms Pb g Pb 1 mol Pb

Atoms  Mass # of atoms x ____1 mole____ x # of grams = Mass 6.02 x atoms 1 mole Example: A party balloon contains 5.50 x atoms of helium gas. What is the mass in grams of the helium? 5.50 x atoms He x 1 mol He x 4.00 g He = g He 6.02 x atoms He 1 mol He

Atoms  Mass Practice Problem # of atoms x ____1 mole____ x # of grams = Mass 6.02 x atoms 1 mole Practice: How many grams of mercury are in 1.19 x atoms of mercury gas? 1.19 x atoms Hg x 1 mol Hg x g Hg = 39.7 g 6.02 x atoms Hg 1 mol Hg Hg