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THE MOLE CALCULATIONS
The Mole: A Chemists' Dozen
Avogadro's constant (NA) = 6.02 x 1023 of something
molar mass (M)
-the mass of a mole of a substance ex. Mc = 12.01 g/mol
-expressed in grams per mole
- a value given on the periodic table (atomic mass is also molar mass)
molar mass of compounds
- the sum of the molar mass of its components
HW TAKE-UP . p. 81 # 1, 2,3
p. 85 # 4
CALCULATIONS USING THE MOLE
Symbol
n
m
M
N
NA
Quantity
Number of moles
mass
Molar mass
Number of entities
Avogadro’s constant
6.02 x 10 23
Unit
mol
g
g/mol
Atoms, ions, formula units, molecules, pillows…
----
Calculating the number of entities
Ex 1. how many candies are in a bag of 198 g if five candies have a mass of
______?
Have:
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Bag = 198 g
5 candies = __g
Need: number of candies in 198 g bag
Conversion factors
5 candies/ ___g
___g / 5 candies
Subsitute in: (units in denominator of conversion factor have to be same)
Need = key values x conversion factor
Number of candies = 198 g x 5 candies / ____g
So there are….
 count ‘em (Werther’s Originals mmm…)
Ex 2. How many dozen playing cards are in a box containing 558 g of cards if
one playing card has a mass of 1.5 g?
558 g x 1 dozen/ 12 x 1.5 g = 31 doz
Ex 3. How many oxygen molecules, O2 are in a cylinder containing 48.0 g of
oxygen if 6.02 x 1023 oxygen molecules have a mass of 32.00 g?
Have:
m = 48 g of oxygen
M = 32.00 g/ mol
So 6.02 x 1023 molecules/32.00 g
Need: number of oxygen molecules
Number of O2 molecules = 48 g of oxygen x 6.02 x 1023 molecules/32.00 g
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Ex 4. What amount of iodine molecules, I2, is in 2.462 kg of iodine is 4
mol of iodine has a mass of 507.6 g?
Mass, Molar mass, and Entities
ex1 . calculate the mass, in grams of 2.5 mol of calcium ions
ex2. what amount of gold, in moles, is in a 100 g nugget of pure gold? How many
atoms of gold are in a 100 g nugget of pure gold?
ex3. Sodium fluoride, NaF(s) , is added to toothpaste and water to prevent
tooth decay. Calculate the mass of 2.00 mol of NaF(s).
m 1 mol
m 2 mol
ex4. My bumper fell off! It had turned into iron III oxide (Fe2O3) over the
winter! What amount of iron III oxide is in a 2 kg sample?
ex5. How many atoms of oxygen are in the 2 kg sample?
HW extension exercise (to be handed in Friday)
Counting Molecules, Atoms, and Chocolate Assignment
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COUNTING ATOMS, MOLECULES, AND OTHER ENTITIES
Use the following materials to measure and/or calculate the quantity described in
each step below. Attach a separate piece of paper showing your calculations.
Materials:
balance, plastic pipettes, beaker, copper penny, chalk, water
Methods:
1. Determine the mass of a drop of water by measuring the mass of 50 drops of water.
mass of 50 drops =
mass of 1 drop =
How many molecules of water are in one drop?
mass of 1 drop x 1/M H2O = moles of H2O in 1 drop
1 mole = 6.02 x 10 23 molecules of water
moles x molecules/mole
molecules of water in 1 drop =
2. Assuming that a penny contains only copper, calculate the number of copper atoms in a
penny.
mass of a penny =
number of copper atoms =
mass x molar mass = moles
1 mole of Cu = 6.02 x 10 23 Cu atoms
4. You dissolved 3.00 g of table salt, NaCl (s) in 200.00 mL of water. Calculate the number of
sodium ions in the salt solution.
MNaCl =
formula units of salt in 3.0 g
mass x 1/M = moles of NaCl
1 mole = 6.02 x 10 23 formula units NaCl
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number of sodium ions in salt =
5. Measure the mass of a piece of chalk. Use the piece of chalk to write the full
names (first and last) of all your group’s members on the blackboard. Assuming that the
chalk is made entirely of calcium carbonate, calculate the number of molecules that you used
to write your name.
mass of chalk before writing =
mass after writing =
formula calcium carbonate=
mass of chalk used to write =
number of molecules of calcium carbonate =
M=