Unit 5 Assignment Packet
Name:____________________________
Period:______
A1: Mole Conversions
1. Identify the representative particle in each of the following: (atom, molecule, formula unit)
a. CuSO4
b. H2O
c. NaCl
d. Zn
e. Cu
f. CO2
2. How many atoms are present in the following compounds?
a. Barium sulfide
b. O3
c. Chlorine gas
d. Silver phosphate
e. Iron (III) nitrate
f. Phosphorus Pentachloride
3. Consider the following samples: 1.00 mol H2O2, 1.00 mol C2H6, or 1.00 mol CO
a. Explain which sample contains more molecules?
b. Explain which sample contains more atoms?
4. Write the relationship between the mole and Avogadro’s number.
5. Calculate the number of representative particles (molecules, formula units, atoms) or moles for each of
the following using Avogadro’s number:
a. 8.2 mol copper (II) sulfate
b. 8.67 x 1018 atoms Zn
c. 343.67 mol H2O
d. 328 formula units H3PO4
6. Calculate the molar mass of each of the following using the periodic table:
a. CO2
b. C6H12O6
c. Carbon tetrachloride
d. HNO3
e. Fe
f. Copper (I) hydroxide
7. Write the relationship between the mole and molar mass.
A2: More Mole Conversions
1. Calculate mass to moles, or moles to mass for each of the following:
a. 142.7 g NaHCO3
b. 13.87 mol copper (II) chloride
c. 3.14 x 103 mol HCl
d. 8.63 x 10-3 g CaCO3
2. Write the relationship between the mole and molar volume at STP.
3. Calculate the volume in liters or moles for each of the following at STP using molar volume:
a. 27 L NO2
b. 3.5 mol H2
c. 2.30 x 101 L HCN
d. 0.250 mol O2
4. Calculate the required information for each problem:
a. Atoms of carbon in 87.6 grams of carbon dioxide
b. Volume in liters of 100.0 grams of gaseous oxygen at STP
c. Mass in grams of 9.2 x 1021 NaCl formula units
d. Volume in liters of 1.33 x 1024 N2 molecules
e. Mass in grams of 300 molecules of H2O
f. Number of H atoms in 6.047 x 1023 molecules of H2
g. Mass in grams of O atoms in 13.7 grams of sulfur dioxide
h. If a balloon is filled with 13.2 liters of oxygen gas
A2: Percent Composition
Percent Composition:
Example
The percentage by mass of each element in a compound.
Calculate the mass of each element in potassium carbonate, K2CO3.
First calculate the molar mass for K2CO3. Find the atomic mass of each element from the periodic table.
Multiply it by the number of times it appears in the formula and add up the total.
2 Potassium atoms
1 carbon atom
3 Oxygen atoms
K
C
O
2 x 39.10
1 x 12.01
3 x 16.00
=
=
=
78.20
12.01
48.00
138.21
To find the percent of each element divide the part of the mass that pertains to that element with the total mass
Percent of Potassium
K=
78.20
138.21
X 100
=
56.58 %
Percent of Carbon
C=
12.01
138.21
X 100
=
8.69 %
Percent of Oxygen
O=
48.00
138.21
X 100
=
34.73 %
Percent Composition Calculations
Using the example above, calculate the percentage composition of each element in the formulas shown below.
Show your work and circle your answers.
1. Magnesium carbonate MgCO 3
2.
Sulfuric Acid H2SO4
3.
4.
If you have 18.65 g of Sodium Nitrate, NaNO3, how many grams of oxygen are in the sample?
A hydrated salt (a salt with water loosely bound to it) has a mass of 12.33 g. The salt is heated in a
crucible to remove the water. After heating, the anhydrous salt (a salt without water attached to it) has a
mass of 9.25 g. What is the percent composition of water in the hydrated salt?
A4: Empirical Formula
Empirical Formulas: The lowest whole number ratio of elements in a compound
Example What is the empirical formula for a compound which contains 41.1% iron, 23.6% sulfur and 35.3%
oxygen?
First assume each % is a mass in g’s (corresponding to a total substance mass of 100.00 g). Find the atomic
mass of each element from the periodic table and use it to convert the mass in grams to moles.
41.1 g Fe
23.6 g S
35.3 g O
Fe: 55.845g/mol
S: 32.065g/mol
O: 15.999g/mol
(41.1g)/(55.845g/mol)
(23.6g)/(32.065g/mol)
(35.3g)/(15.999g/mol)
=
=
=
0.736 mol Fe
0.736 mol S
2.21 mol O
Next, convert the mole values to lowest whole number mole ratios. Do this by dividing each mole value by the
smallest mole value of the group. These whole numbers tell the empirical formula ratios.
0.736 mol Fe
0.736 mol S
2.21 mol O
0.736 mol
0.736 mol
0.736 mol
0.736mol/0.736mol
0.736mol/0.736mol
2.21/0.736
Empirical Formula
=
=
=
1
1
3
FeSO3
Empirical Formula Calculations
Show your work. Remember to first convert values to moles and then determine the lowest whole number mole
ratio.
1. Find the empirical formula for a compound which contains 32.8% chromium and 67.2% chlorine.
2. What is the empirical formula for a compound which contains 80.1% zinc and the rest is oxygen?
3. The characteristic odor of pineapple is due to ethyl butyrate, an organic compound which contains only
carbon, hydrogen and oxygen. If a sample of ethyl butyrate is known to contain 0.62069 g of carbon,
0.103448 g of hydrogen and 0.275862 g of oxygen, what is the empirical formula for ethyl butyrate?