Lecture 54 – Lecture 55
Moles of Compounds
Ozgur Unal
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A chemical formula indicates the numbers and types of
atoms contained in one unit of the compound.
Example: NaCl or Mg(NO3)2 etc.
1 NaCl contains 1 Na atom and 1 Cl atom
1 Mg(NO3)2 contains 1 Mg atom, 2 N atoms and 6 O atoms
How about moles of compounds?
How many moles of Cl- are there in 1 mole of NaCl?
How many moles of Na+ are there in 3 moles of NaCl?
How many moles of N are there in 1 mole of Mg(NO3)2?
How many moles of O are there in 2 moles of Mg(NO3)2?
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Example: Zinc chloride is used in soldering flux, an alloy
used to join two metals together. Determine the moles of Clions in 2.5 mol ZnCl2.
Example: Plants and animals depend on glucose C6H12O6
as an energy source. Calculate the number of moles of each
element in 1.25 mol C6H12O6.
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The mass of your backpack is the sum of the pack and the
masses of the books, notebooks, pencils and other items.
Similarly, the molar mass of a compound is the sum of the
molar masses of the elements in the compound.
Example: Molar mass of K2CrO4
Molar mass of K: 39.1 g/mol
Molar mass of Cr: 52.0 g/mol
Molar mass of O: 16.0 g/mol
Molar mass of K2CrO4: 2*K + Cr + 4*O = 194.2 g/mol
Example: Determine the molar mass of each compound
below:
CaCl2
C2H5OH
KC2H2O2
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Example: The characteristic odor of garlic is due to allyl
sulfide, (C3H5)2S. What is the mass of 2.5 mol of (C3H5)2S?
Example: The United States chemical industry produces
more sulfuric acid (H2SO4), in terms of mass than any other
chemical. What is the mass of 3.25 mol of H2SO4?
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Example: Calcium hydroxide is used to remove sulfur
dioxide from the exhaust gases emitted by power plants and
for softening water by the elimination of Ca+2 and Mg+2 ions.
Calculate the number of moles of calcium hydroxide in 325 g
of the compound.
Example: Determine the number of moles present in each
compound:
22.6 g AgNO3
6.5 g ZnSO4
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Example: AlCl3 is used in refining petroleum and
manufacturing rubber and lubricants. A sample of AlCl3 has a
mass of 35.6 g.
How many Al atoms does the sample contain?
How many Cl atoms are present?
Example: Ethanol C2H5OH, a domestically produced fuel
source in the US, is often blended with gasoline. A sample of
ethanol has a mass of 45.6 g.
How many C atoms does the sample contain?
How many H atoms are present?
How many O atoms are present?
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