How do we use the mole?
Chemistry Unit 9: Homework Packet
______/ 145pts
Name:____________________
Work is expected for full credit on all problems.
New Skills
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Convert mass, moles and number of atom/molecules
Use compound formulas to calculate molar mass
Determine percent composition of a compound
Determine empirical and molecular formulas of a compound
Calculate the formula of a hydrate
Apply mass and mole conversions to balanced reactions
9.1 Measuring Matter – Chemists use the mole to count atoms, molecules, ions and
formula units.
1. (3pts) Explain how a mole is used to indirectly count the number of particles of
matter.
a. How is the mole used in chemistry?
2. (4pts) Relate the mole to a common everyday counting unit.
a. What is a common unit that is used for counting and how is it similar to a mole?
3. Convert between moles and number of representative particles.
a. (4pts) How many particles are in 6.5 mols?
b. (4pts) How many moles of atoms are in 6.63 x 1026 atoms?
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9.2 Mass and the Mole – A mole always contains the same number of particles, however,
moles of different substances have different masses.
1. Relate the mass of an atom to the mass of a mole of atoms.
a. (4pts) The mass on the periodic table can be listed in two different ways. What
are the two different units that are used?
2. Convert between number of moles and the mass of an element.
a. (4pts) If I need 4 mols of Cu, how do I measure the amount? Be specific.
b. (4pts) I measured 8.20g of Manganese, how many atoms do I have?
3. Convert between number of moles and number of atoms of an element.
a. (6pts) How many atoms of copper are in a U.S. penny (assuming solid copper)
with a mass of 2.5g?
b. (6pts) How much does 12.8 x 1025 atoms of silver weigh?
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9.3 Moles of Compounds- The molar mass of a compound can be calculated from its
chemical formula and can be used to convert from mass to moles of that compound.
1. Recognize the mole relationships shown by a chemical formula.
a. (3pts) How are mole relationships shown in a chemical formula?
2. Calculate the molar mass of a compound.
a. (12pts) Find the molar mass of the following compounds/molecules.
MgSO4
H3PO4
Fe(NO3)2
3. Convert between the number of moles and mass of a compound.
a. (6pts) What is the mass of 4.5 mols of H2SO4?
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4. Apply conversion factors to determine the number of atoms or ions in a known mass
of a compound.
a. (6pts) Calculate the number of moles of Ca(OH)2 in 455 g of the compound?
b. (6pts) How many atoms are in 567g of calcium phophate?
9.4 Empirical and Molecular Formulas – A molecular formula of a compound is a
whole-number multiple of its empirical formula
1. Explain what is meant by the percent composition of a compound.
a. (3pts) Define percent composition.
b. (6pts) What is the percent by mass of each element in CaCO3?
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2. Determine the empirical and molecular formulas for a compound from mass percent
and actual mass data.
a. (6pts) What is an empirical formula? How does this compare to the molecular
formula? Are they the same?
b. (6pts) A compound has the following mass percentages: C = 40.684%, H =
5.121%, O =54.195%. What is the empirical formula for this molecule?
c. (9pts) The mass of a hydrocarbon (a molecule with carbon and hydrogen),
octane, has been experimentally determined to be 114.229g. We know that
octance is 84.117% C by mass and 15.883% H by mass. What is the empirical
and molecular formula of octane?
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3. Explain what a hydrate is and relate the name of the hydrate to its composition.
a. (4pts) What is a hydrate? What is anhydrous?
b. (3pts) How are hydrates named?
4. Determine the formula of a hydrate from laboratory data.
a. (12pts) A mass of 5.50g of hydrated magnesium sulfate is placed in a crucible
and heated. After heating, 2,68g of white anhydrous magnesium sulfate
(MgSO4) remains. What is the formula for the hydrate? Name the hydrate.
9.5Accumulating Content and Skills:– Chemistry content is continuous and builds on
prior knowledge and skills. This section will combine this unit with previous units.
1. Apply knowledge and skills from previous units to content learned in this unit.
a. (3pts) How does the mole apply to balanced equations?
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b. (12pts) How many grams of each reactant are needed to run the following
reaction? How many grams of each product are produced? (Hint: complete,
balance, convert)
MgSO47H2O(aq) + CaCl2(aq) 
c. (9pts) From the reaction above, how much is needed of each reactant in the net
ionic equation to produce the balanced amount of the precipitate? How much
precipitate is produced?
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