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11.2 Mass and the Mole
Objectives:
 Calculate the number of moles in a given mass of an
element and the mass of a given number of moles of
an element
 Calculate the number of moles of an element when
given the number of atoms of the element
 Calculate the number of atoms of an element when
given the number of moles of the element
11.2 Mass and the Mole
Vocabulary
 Molar mass
The Mass of a Mole
 Moles of different substances have different masses
just like a dozen tennis balls has a different mass than
a dozen baseballs
The Mass of a Mole
 Molar Mass- The mass in grams of one mole of any
pure substance
 Units: grams/mol
 Example: Manganese has an atomic mass of 54.94 amu
there fore it has a molar mass of 54.94 g/mol
PROBLEM:
FIND THE MOLAR MASS OF:




1) Mn
54.9 g/mol
2) Ca
40.1 g/mol
3) Xe
131.3 g/mol
4) How many particles do you
have of each?
 5) If you had 6.02 x 1023 atoms
of uranium, how many grams
would you have?
•When you measure the molar mass of an element on
the balance, you are measuring 6.02 x 1023 atoms!
Using molar mass
# of moles X # of grams =
mass
1 mole
# grams X 1 mole
=
# of grams
moles
Using molar mass
 Converting mass to moles and moles to mass
Given:
Given:
Multiply by M.M
Divide by M.M
Mole Map
PROBLEMS:
1) How many grams in 3.00 mol C?
 Note: molar mass of C: 1 mole = 12.0 g
 3.00 mol C x __12.0 g
1 mole
 = 36.0 g C
2) Calculate the moles in 3.2 g Oxygen, O2.

Molar mass: 1 mol=32.0g
 3.2 g O x 1 mole
32.0 g
 = 0.10 mol O2
PROBLEM - Mass to Atoms Conversions
(2 steps)
Find the atoms in 25.0 g of Gold (Au).
 Step 1: Find moles Au (use molar mass)
 25.0 g Au x 1 mole

197.0 g
= 0.1269 mol

(keep digits in calc.)
 Step 2: Find atoms (Av.#)
 0.1269 mol x 6.02 x 1023 atom

1 mole
 = 7.64 x 1022 atoms Au
PROBLEM: Calculate the mass of
4.0 x 1022 atoms Al.
Use mole map to draw out path from atoms  g
 Step 1: Use Avogadro’s # to find # moles:
 4.0 x 1022 atoms Al x ___1 mole

6.02 x 1023 atoms
 = 0.66 mol Al
 Step 2: Use molar mass to convert to grams:
 0.664 mol Al x 27.0 g

1 mol
 = 1.8 g
(round off at end!)
http://www.moleday.org/htdocs/gifs/Moles%20of%20the%20Caribbean[1].JPG
11.3 Moles of Compounds
Objectives:
 Recognize the mole relationships shown by a chemical
formula
 Calculate the molar mass of a compound
 Calculate the number of moles or a compound and the
mass of a compound from a given number of moles of
compound
 Determine the number of atoms or ions in a mass of a
compound
Chemical Formulas and the
Mole Ratio
 The subscripts within a chemical formula also
represent molar ratios among the elements of the
compound
 Consider the compound:
CCl2F2
 The ratio of elements is: C to Cl to F
1 :
2 : 2
 Thus there is a molar ratio of 1 mole of carbon to 2
moles of chlorine to 2 moles of fluorine.
Chemical Formulas and the
Mole Ratio
 The compound to element mole ratio is:
 Consider the compound:
1 mole of CCl2F2
 The ratio of elements is:



1 mol C to 1 mole of CCl2F2
2 mol Cl to 1 mole of CCl2F2
2 mol F to 1 mole of CCl2F2
1:1
2:1
2:1
The Molar Mass of Compounds
 Molar mass of a compound is determined by adding the
masses of all elements present.
# of moles x molar mass = number of grams
 Example: K2CrO4
2 mol K x 39.10 g K = 78.20 g
1 mol K
1 mol Cr x 52.00 g Cr = 52.00 g
1 mol Cr
4 mol O x 16.00 g O = 64.00 g
1 mol O
78.20 g
52.00 g
+
64.00 g
194.20 g K2CrO4
CHEMICAL FORMULA Converting to moles of
individual atoms (or ions) given formula:
 C6H12O6 (glucose):
 1.0 mole glucose contains:
 6.0 mol C atoms
 12.
mol H atoms
 6.0 mol O atoms
 Problem: How many
moles of each atom in
 Phosphoric acid, H3PO4
 3 mol H atoms, 1 mol P at,
4 mol O at.
MOLAR MASS OF COMPOUNDS:
 1) Find molar mass of water, H2O.
 # moles X molar mass = # grams
 (formula) (periodic table)



H= 2
O=1
Total
x 1.0 g
x 16.0g
= 2.0 g
=16.0 g
18.0 g = 1 mole
Converting moles to mass:
PROBLEM: Find mass of 3.2 moles ammonia, NH3.
 Find molar mass of NH3 & plug in:
 N = 1 x 14.0 g = 14.0 g
 H = 3 x 1.0 g = 3.0 g

17.0 g = 1 mol
3.2 mol NH3 x __17.0 g_____

1 mol
 = 54 g NH3.
=
Converting mass to moles:
PROBLEM: Find moles in 8.8 g of CO2 .
 8.8 g CO2 x

1 mol
g
 Find molar mass CO2: C = 1 x 12.0 = 12.0
O = 2 x 16.0 = 32.0
44.0g/mol


 8.8 g CO2 x

1 mol
44.0 g
 = 0.20 mol CO2.