The Mole Mrs Coyle Chemistry Part I The

The Mole Mrs. Coyle Chemistry

Part I • The Mole • Molar Mass • Moles <->Particles

-How do we measure the mass of chemical quantities? -amu’s -grams -moles

Atomic Mass Unit (amu): = 1/12 of the mass of a 12 C atom

Relationship of amu to gram 1 amu = 1. 66054 x 10 -24 g

Atomic Mass: -The weighted average of the masses of the naturally occurring isotopes of an element. -The atomic mass of an element is listed on the periodic table.

Why the Mole? Are the quantities scientists use on a lab scale at the level of the atom or at the level of grams?

The Mole = 6. 02 x 1023 One mole of atoms (6. 02 x 1023 atoms) of an element is contained in an amount equal to its atomic mass measured in grams. This mass is called molar mass.

Molar Mass of an Element: an amount equal to the atomic mass of the element expressed in grams. • Example: for Neon, Atomic Mass = 20. 18 amu Molar Mass = 20. 18 g

Molar Mass of a Compound: an amount equal to the molecular mass expressed in grams. • • • Also known as, Gram-Formula Mass, Molecular Weight. Examples: What is the molar mass of: H 2 O H 2 SO 4 Mg(NO 3)2 Cu. SO 4 ∙ 5 H 2 O

The Definition of The Mole The mass of an element or compound that contains as many elementary (representative) particles (atoms, molecules, ions, etc. ) as there atoms in exactly 12 grams of 12 C.

How many atoms are there in 12 g of C-12 ? 6. 022145 x 23 10 atoms 1 mole of atoms (mol) Avogadro’s Number

Avogadro’s Number • Can be used the same way the word “dozen” is used to mean 12 for any object. • One mole of books is 6. 022 x 1023 books, just like a dozen books is 12 books.

“Mole of Atoms of Hydrogen” 1 atom Atomic Mass: 1. 008 amu 1 mole of atoms: Molar Mass: 1. 008 g 6. 022 x 1023 atoms

“Mole of Molecules of Hydrogen” 1 molecule= 2 atoms Molecular Mass: 2. 016 amu 1 mole of molecules= Molar Mass: 1. 008 g 6. 022 x 1023 molecules= 2 x 6. 022 x 1023 atoms

Problem Solving Methods • Using Mathematical Formulas • Factor-Label Method

Mathematical Formulas #mol= Mass of Sample (g) Molar Mass (g/mol) #particles=#mol x 6. 022 x 10 23 particles/mol particles can be atoms, molecules, formula units, etc.

Equalities Used in Factor- Label Method 1 mol = Molar Mass g 1 mol= 6. 022 x 10 23 particles (atoms, molecules, formula units, etc)

Problem # 1 - Moles to Atoms • How many atoms are there in 6 moles of Fe?

Solution using Factor-Label Method • 6 mol of Fe x 6. 02 x 1023 atoms Fe = 1 mol Fe =3. 6 x 10 24 atoms

Solution using Math Formula • #atoms=#mol x 6. 022 x 10 23 atoms/mol= =6 mol of Fe x 6. 02 x 1023 atoms Fe/mol= =3. 6 x 10 24 atoms

Problem #2 –Moles to Atoms • How many iron atoms are there in 6 moles of iron (III) oxide? A: 7. 2 x 10 24 atoms

Problem #3 - Atoms to Moles • How many moles of H 2 O are there in 18. 06 x 10 23 molecules of H 2 O? • A: 3 moles of H 2 O

Part II • Moles Mass Problem

Problem # 4 –Mass to Moles, Mass to Atoms For a sample of 20. 0 g of iron, Fe, calculate: a) the number of moles of atoms b) the number of atoms • Solution using Math Formula Method: a) #mol Fe= mass Fe(g) = 20 g Fe molar mass Fe(g/mol) 55. 85 g/mol #mol Fe = 0. 358 mol Fe atoms

Problem # 4 Cont’d b) #atoms Fe= #mol x (6. 022 x 1023 atoms/mol)= = (0. 358 mol Fe)(6. 022 x 10 23 atoms/mol) #atoms Fe= 2. 156 x 1023 atoms Fe

Problem # 5 For a sample of 150. 0 g of H 2 SO 4, calculate: a) The number of moles of H 2 SO 4 present. b) The number of oxygen atoms present. Solution: MM H 2 SO 4 = H: (2 atoms)(1. 008 g/mol) S: (1 atom)(32. 07 g/mol) O: (4 atoms)(16. 00 g/mol) 98. 09 g/mol

Problem # 5 • # mol H 2 SO 4 = Mass (g) =150. 0 g H 2 SO 4 MM (g/mol) 98. 09 g/mol # mol H 2 SO 4= 1. 529 mol H 2 SO 4

Problem # 5 Cont’d b) #atoms of O = (#mol O)(6. 022 x 1023 atoms)= = (4 x 1. 529 mol O) (6. 022 x 1023 atoms) = = 3. 683 x 1024 atoms O

Part III • Molar Volume of an Ideal Gas at STP

Molar Volume of an Ideal Gas • At STP conditions, Standard Temp of 0 deg C and Standard Pressure of 1 atm, the molar volume of an ideal gas is 22. 4 L

• For an ideal gas at STP: #mol= Volume (L) 22. 4 (L/mol) or 1 mol = 22. 4 L

Problem # 6 -Volume to Atoms • How many atoms of oxygen are there in 44. 8 L of oxygen gas at STP? • Solution: #mol O 2= Volume (L) = 44. 8 L = 2. 00 mol O 2 22. 4 (L/mol) 22. 4 L/mol #atoms O =#mol x 6. 022 x 10 23 atoms/mol = 2 x (2. 00 mol O)(6. 022 x 10 23 atoms/mol) #atoms O= 2. 41 x 1024 atoms O

Problem #7 - Molecules to Volume • How many L at STP are contained in a sample of 8. 6 x 10 24 molecules of CO 2 gas? A: 320 L

Part IV • Density of a Gas at STP from Molar Mass.

Density • D= Mass = Volume Molar Mass Molar Volume At STP, Molar Volume of an Ideal Gas = 22. 4 L

Problem #8 - Density of a Gas from MM • What is the density of NO 2 gas at STP? • A: 2. 05 g/L