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Chapter 7
Chemical Quantities
The Mole (Friend or foe)
What is a mole?
1. SI base unit to measure the
amount of a substance
2. The amount of a substance that
contains the same number of particles
as the number of atoms in exactly 12 g
of carbon-12
 What is Avogadro’s number?
1. the number of particles in a mole
2. 1 mole = 6.02 x 1023 particles
3. particles are: atoms, ions, molecules,
formula units
• How do you use these numbers?
1. 1 mole of C = 6.02 x 1023 atoms C
2. 1 mole of NaCl = 6.02 x 1023 formula
units NaCl
3. 1 mole of H2O = 6.02 x 1023 molecules
H 2O
4. 1 mole of Ca+2 = 6.02 x 1023 ions Ca+2
• What is molar mass?
1. the mass in grams of one mole of a
pure substance (element or compound)
2. use the periodic table to find the mass
3. What is the molar mass of helium?
4.0 g He
mole
4. will be used as a conversion factor
5. Examples:
a. What is the molar mass of 1 mole of
Al?
27.0 g Al
mole
b. What is the molar mass of 1 mole of
CO2? C = (1)(12.0) = 12.0
O = (2)(16.0) = 32.0
44.0 g/mole
 Converting from moles to grams
1. What is the grams of 3.50 mole of Cu?
2. There are 11.9 g of Al, how many
moles of Al are there?
3. How many moles are in 25.0 grams of
H3PO4?
• Converting moles to molecules
1. How many molecules are in 5.2 moles of
NaCl?
2. How many moles are in 3.12 x 1015 Mg+2
ions?
• Convert grams to molecules.
1. How many molecules are in 3.14 grams
of NaOH?
2. How many grams are in 4.12 x 1012
molecules of Rh?
3. How many molecules are in 523 g of KI?
Percent Composition
1. Definition – the percent by mass of
each element in the compound
2. Formula:
% composition = mass of element
100
mass of compound
3. Ex.
Find the percent composition of
copper (I) sulfide.
Cu2S
Cu = 2(63.5) = 127.0
S = 1(32.1) = 32.1
159.1g/mole
%Cu = 127.0 100 = 79.8%
159.1
%S =
Empirical Formula
1.Shows the simplest whole-number
ratio of the atoms in a compound
2. Examples:
a.) C2H8 =
b.)
Al2O3 =
3. Examples:
Analysis shows a compound to
contain 26.56% K, 35.41% Cr,
38.03% O. Find the empirical
formula.
Molecular Formula
1. Indicates the ratio of the atoms
2. Indicates the actual number of atoms
3. n = Molecular mass
empirical mass
4. (empirical formula)n = molecular formula
5. Examples:
An organic compound is found to contains
92.25% C and 7.75% H. If the molecular mass
is 78, what is the molecular formula?