Molar Mass & Conversions

The Mole

mole (mol)- SI Unit for the amount of a substance that contains as many particles as there are atoms in exactly 12g of carbon-12.

•A unit of counting, like the dozen.

Avogadro’s NumberAvogadro’s Number - the number of

particles in exactly one mole of a pure substance.

1 mole = 6.0221415 X 1023

1 mol = 6.022 x 1023

Amedeo Avogadro

Atomic Massatomic mass - the mass of one mole of an

atom•Atomic mass is expressed in atomic mass

units (amu) or (u) or g/mol.•Can be found on the periodic table.•All atomic masses are based on the

atomic mass of carbon-12 being 12 amu.

Molar Mass

molar mass - the mass of one mole of a pure substance.

•Molar mass is written in units of amu or g/mol.

Atomic mass vs. Molar mass

•atomic mass - the mass of one mole of an atom.

•molar mass - the mass of one mole of a pure substance.

Atomic Mass vs. Molar Mass

Example Atomic Mass Molar Mass

Na

Ag

C

O

22.99 g/mol 22.99 g/mol

107.87 g/mol

107.87 g/mol

12.01 g/mol 12.01 g/mol

16.00 g/mol 16.00 g/mol

Molar Mass of Compounds

Compound Molar Mass

H2O

C6H12O6

NaCl

Cl2

(NH4)3PO4

CuSO4·5H2O

18.02 g/mol

180.18 g/mol58.44 g/mol

70.90 g/mol

149.12 g/mol249.72 g/mol

Introduction to Molar Conversions

Amount Mass

1 mol O2

½ mol O2

2 mol O2

3 mol O2

32.00 g

16.00 g

64.00 g

96.00 g

Grams to MolesConverting grams to moles: divide by molar mass.

1. How many moles of Ca are in 5.00g of Ca?

2. How many moles of H2O are in 36.0g of H2O?

3. How many moles of AgNO3 are in 124.5g of AgNO3?

1 mol Ca5.00g Ca x =

40.08 g Ca0.125 mol Ca

22

2

1 mol H O36.0 g H O x =

18.02 g H O 22.00 mol H O

33

3

1 mol AgNO124.5 g AgNO x =

169.88 g AgNO0.7329

3mol AgNO

Moles to Grams

Converting from moles to grams: multiply by molar mass.

1. What is the mass in grams of 2.25 moles of Fe?

2. What is the mass in grams of 0.896 moles of BaCl2?

55.85 g Fe2.25 mol Fe x =

1 mole Fe 126 g Fe

2187 g BaCl

Types of Particles•Atoms – C, Cu, He

•Molecules – O2, C12H22O11, CO2 (all nonmetals in the formula)

•Formula units – NaCl, CaCl2, Mg(NO3)2 (includes a metal in the formula)

Particles to MolesConverting particles to moles: divide by Avogadro's Number.

1. How many moles of Pb are in 1.50 X 1025 atoms of Pb?

2. How many moles of CO2 are in 6.78 X 1021 molecules of CO2?

2.49 x 101 moles Pb

1.13 x 10-2 moles CO2

Moles to ParticlesConverting moles to atoms: multiply by Avogadro's Number.

1. How many molecules of NO are in 0.87 moles of NO?

2. How many formula units of NaI are in 2.50 moles of NaI?

5.2 x 1023 molecules NO

1.51 x 1024 formula units NaI

Grams to Moles to Particles

Example: How many molecules of N2 are in 57.1g of N2?

257.1 g N x 2

2

1 mol N

28.02 g N

232

2

6.02 x 10 molecules Nx

1 mol N

242= 1.23 x 10 molecules N

Particles to Moles to Grams

Example: How many grams of NaF are in 7.89 X 1024 formula units of NaF?

247.89 x 10 f.un. NaF x 23

1 mol NaF

6.02 x 10 f.un. NaF

41.99 g NaFx

1 mol NaF

= 550. g NaF

Atoms to Moles to Grams

Tough Example:

How many total atoms are in 235 g of CO2?

9.64 x 1024 total atoms

The Mole Bridge