Download The Mole Essential Question To what extent is it

The Mole
Essential Question
To what extent is it advantageous to look at chemical composition in terms of
moles instead of mass?
How do we measure matter?
 Mass
o Buy potatoes by the kilogram, pound, gram, or ounce
 Volume
o Gasoline – gallon, liter
o Liquid medicine – milliliter
 Count
o Soda – 6, 12, 24, or 36 packs
 Sometimes we use specific words to mean a certain amount
o Pair – 2
o Dozen – 12
 Conversion factors
o We use conversion factors everyday
Example – 1 dozen = 12 eggs  this can be set-up like this to be used
as a conversion factor.
The format you use
depends on how you are using the conversion factor.
Example 2 – Apples
Example Problem, if 0.20 bushel is 1 dozen apples and a dozen apples has a mass
of 2.0 kg, what is the mass of 0.50 bushel of apples?
Assume 2.0 kg of apples is 1 dozen and that each apple has 8 seeds. How many
apple seeds are in 14kg of apples?
Mole – 6.02 x 1023 representative particles of a substance
Avogadro’s number
(SI unit for measuring the amount of a substance)
What is a representative particle?
Ionic compound – formula unit
Molecular compound (covalently bonded) – molecule
Ion – ion example Ca+2
Element – atom
1 mole of any substance contains Avogadro’s number of representative particles
Converting # of particles to moles
What is the conversion factor?
Example problem 1:
Magnesium is a light metal used in the manufacture of aircraft, automobile
wheels, tools, and garden furniture. How many moles of magnesium is 1.25 x 1023
atoms of magnesium?
Example Problem 2:
How many moles of 2.17 x 1023 representative particles of bromine?
Converting moles to number of particles
What is the conversion factor?
Example problem 3:
Propane is a gas used for cooking and heating. How many atoms are in 2.12 mol
of propane (C3H8)?
Example Problem 1 Answer:
Example Problem 2 Answer:
Example Problem 3 Answer:
Molar Mass
Element
 On the periodic table the atomic mass of an element is reported in amu.
(atomic mass units).
 Relative to the mass of C-12.
o Why are these not whole numbers?
 Since we cannot use units of amu in the lab, this scale has been converted
to masses measured in grams.
 The mass of an element is expressed in grams/mole. The mass is the
number of grams of 1 mole of that element. Molar mass
Molar mass of a compound
(Also can be called gram formula mass, gram atomic mass, gram molecular
mass, molecular weight)
You need:
The formula of the compound
Atomic numbers of the elements in the compound
Must account for the number of atoms of each element
Example 4:
The decomposition of hydrogen peroxide (H2O2) provides sufficient energy to
launch a rocket. What is the molar mass of hydrogen peroxide?
Molecular formula: H2O2
H = 1.01 g/mol
O = 15.99 g/mol
(1.01 g/mol x 2) + (15.99g/mol x 2) = 34.00 g/mol
or
2.02 g H + 31.98 g O = 34.00 g/mol