 Chemists use the mole to count microscopic particles.
 How many socks come in a pair?
 2
 How many eggs are in a dozen?
 12
 How many eggs come in a gross?
 144
 How many pencils come in a ream?
 500

 602,213,670,000,000,000,000,000.
 Seriously
 This number was created by an Italian physicist and lawyer named Amedeo Avogadro.
 Its called Avogadro’s Number.
 Is there an easier way to write it?
 6.02 x 10 23 items = 1 mole

 Think about eggs
 1 dozen eggs = 12 eggs
 Conversion factor:
 12 eggs/1 dozen eggs

OR
 1 dozen eggs/12 eggs
 So if you have 3.5 dozen eggs how many eggs do you have?
 3.5 dozen x (12 eggs)/1 dozen = 42 eggs

 If you have 3.5 moles of sugar how many particles of sugar do you have?
 1 mole of sugar = 6.02 x 10 23 particles of sugar.
 Set up the problem:
 3.5 moles x (6.02 x 10 23 particles/1 mole)
 Solve:
 2.107 x 10 24

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Zinc (Zn) is used to form a corrosion-inhibiting surface on galvanized steel. Determine the number of Zn atoms in
2.50 moles of Zn.
1.51 x 10 24 atoms
Calculate the number of molecules in 11.5 mol of water.
6.92 x 10 24 molecules
Silver nitrate Ag(NO
3
)
2 is used to make several different compounds used in photographic films. How many molecules of silver nitrate are there in 3.25 moles of
Ag(NO
3
)
2
?
1.96 x 10 24
How many atoms of oxygen are there in 5.0 mol of oxygen gas?
6.02 x 10 24 atoms

 Calculate the number of moles of Zinc that contains
4.50 x 10 24 atoms.
 0.914 moles
 How many moles can be made up from 5.57 x 10 24 atoms of Al?
 9.55 moles
 How many moles can be made up from 2.5 x 10 25 atoms of Fe?
 41.5 moles

 What would have more mass a dozen eggs or a dozen elephants?
 Why would a dozen elephants have more mass?
 Just like elephants and eggs certain atoms are bigger than others.
 For example Neon is much bigger than Helium.
 Which would have more mass 1 mole of Neon or 1 mole of Helium?

 The molar mass of an element is the mass in grams of one mole of that element.
 Why is this important?
 Molar mass can be used to calculate the number of atoms with out using a microscope.

 If one dozen jelly beans has a mass of 35 g how much mass does 5 dozen jelly beans have?
 175 g
 To convert from Moles to mass you multiply by the molar mass.
 What is the mass of 3.oo moles of copper?
 191 g cu.
 To convert from mass to moles you divide by the molar mass.

 Chromium (Cr), a transition element, is a component of chrome plating. Chrome plating is used on metals and steel alloys to control corrosion. Calculate the mass in grams of 0.045 moles of Cr.
 2.34 g Cr

 Calcium (Ca), the fifth most abundant element on earth, is always found combined with other atoms because of its high reactivity. How many moles of calcium are in 525 g Ca?
 13.1 moles Ca

 The next step is converting a given mass of an element into a number of atoms.
 If we have 550 g of jelly beans and there are 35 g of jelly beans in a dozen how many dozen jelly beans do we have?
 16 dozen
 How many jelly beans are there in 16 dozen?
 192

 Gold (Au) is one of a group of metals called the coinage metals. How many atoms of gold are there in a
U.S. gold eagle coin with a mass of 31.1 g?
 9.51 x 10 22

 Helium (He) is an unreactive noble gas found underground. A party balloon contains 5.5 x 10 22 atoms of helium gas. What is the mass, in grams, of the helium?
 0.366 g

 Textbook (sorry)
 P. 328 # 15(a&b), 16(a&b)
 P. 329 # 17(a&b), 18(a&b)
 P. 331 # 19(a&b), 20(a&b)

 In the compound CCl
2
F
2
 C: 1 how many atoms do we have?
 Cl: 2
 F: 2
 So if we have one mole of CCl
2
F
2 we have one mole of carbon, two moles of Chlorine and one mole of
Fluorine.

 Determine the molar mass of each of the following compounds:
 NaOH
 CaCl
2
 KC
2
H
3
O
2
 C
2
H
5
OH
 HCN


CCl
4
(NH
4
)
3
PO
4

 The characteristic odor of garlic is due to allyl sulfide
(C
3
H
5
)
2
S. What is the mass of 2.5 moles of allyl sulfide?
 What is the mass of 3.25 mol of H
2
SO
4
?

 Calculate the number of moles in 325 g of Calcium hydroxide Ca(OH)
2
?
 Calculate the number of moles in 22.6 g of AgNO
3
.

 Aluminum chloride (AlCl
3
) is used in refining petroleum and manufacturing rubber. How many Aluminum Chloride molecules are present in 35.6 g of AlCl
3
 How many Al atoms are there?
 How many Cl atoms are there?

 Aluminum oxide (Al
2
O
3
) when dissolved in water breaks apart into ions (Al 3+ and O 2) how many moles of Al 3+ will be produced when 1.5 moles of Al
2
O
3 dissolved in water?
are

1.
2.

What is the molar mass of ethanol C
2
H
5
OH?
How many ethanol molecules are present in 45.6 g?
 How many carbon atoms are there in 45.6 g of ethanol?
 How many hydrogen atoms are there in 45.6 g of ethanol?
 How many oxygen atoms are there in 45.6 g of ethanol?

A sample of sodium sulfite Na
2
SO
3 has a mass of 2.25 g
How many molecules of sodium sulfite are there?



How many atoms of sodium are there?
How many atoms of Sulfur are there?
How many atoms of oxygen are there?

 A compound is made up of one or more atoms bonded together.
 Each of the atoms contributes mass to the compound.
 Example:
 The molar mass of NaOH is
 Na – 22.98 g/mol
 O – 16 g/mol
 H – 1 g/mol
 Total: 39.98 g/mol

 Percent composition is calculated by dividing the mass of an individual element by the mass of the whole compound and then multiplying by 100.
 NaOH:
 Percent Composition of Na:
 (22.98/39.98) x 100 = 57.5%
 Percent Composition of O:
 (16/39.98) x 100 = 40%
 Percent Composition of H:
 (1/39.98) x 100 = 2.5%



NaHCO
3
Molar Mass: 84.01 g/mol
 Percent Composition of Na:
 (22.98/84.01) x 100 = 27.37%
 Percent Composition of H:
 (1/84.o1) x 100 = 1.2%
 Percent Composition of C:
 (12.01/84.01) x 100 = 14.3%
 Percent Composition of O:
 (48/84.01) x 100 = 57.14%

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When we know a compounds percent composition we can determine it’s formula.
The empirical formula of a compound is the formula with the smallest whole-number ratio of elements.
Find the empirical formula for a compound that is 40.05% S and
59.95% O.
If we assume that we have 100 g of this compound:
How many grams of Sulfur do we have?
 40.05 g
How many grams of Oxygen do we have?
 59.95 g
Convert from grams to moles:


40.05 g S x 1 mol S/32.07 g S = 1.249 mol
59.95 g O x 1 mol O/16.00 g O = 3.747 mol

 S
1.249
O
3.747
 SO
3
 Sometimes the empirical formula is not the actual formula for the compound.
 Find the empirical formula for hydrogen peroxide which has a molar mass of 34 g/mol and is 5.9%
Hydrogen and 94.1% Oxygen

 A compounds molecular formula is its actual formula
(not always the same as empirical formula)
 To determine the true molecular formula for a compound its molar mass must be known (either looked up or found experimentally).
 Once we know the molar mass and the empirical formula we can find the true formula of the compound.

 Example:

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Acetylene is a highly flammable compound used in blow torches. Acetylene has a molar mass of 26.04 g/mol. It is
92.2% Carbon and 7.8% Hydrogen. What is the chemical formula of Acetylene?
Step 1: Find empirical formula:
CH
Step 2: Calculate molar mass of empirical formula. (If the molar mass is the same as the actual molar mass then the empirical formula is the true formula.)
13.02 g/mol
Step 3: Divide real molar mass by the molar mass of the empirical formula.
26.04/13.02 = 2.000
Step 4: Multiply all atoms in the empirical formula by the answer to the true formula.
C
2
H
2