Chemistry--Unit 3: Chemical Quantities
Practice Problems
I. The Mole: A Measurement of Matter
1) What is the gram molecular mass of sucrose (C12H22O11)? (342.34 g/mol)
2) Calculate the gram formula mass of KMnO4 and Ca3(PO4)2.
(KMnO4 = 158.04 g/mol, Ca3(PO4)2 = 310.18 g/mol)
3) How many moles is 3.52 × 1024 molecules of water?
3.52 1024 molecules 
1 mole
 5.85 mol
6.02 1023 molecules
4) How many atoms of zinc are in 0.60 mol of zinc?
6.02  10 23 atoms
0.60 mol Zn 
 3.61  10 23 atoms
1 mol
II. Mole-Mass and Mole-Volume Relationships
5) Calculate the mass in grams of each of the following.
a. 8.0 mol lead(II) oxide, (PbO)
8.0 mol PbO 
223.2 g
 1785.6 g
1 mol
b. 0.75 mol hydrogen sulfide (H2S)
0.75 mol H 2 S 
34.08 g
 25.56 g
1 mol
c. 1.50 × 1025 molecules of molecular oxygen (O2)
1.50  10 25 molecules 
1 mole
32.00 g

 797.3 g
23
6.02  10 molecules 1 mole
d. 2.30 × 1030 atoms of iridium
2.30  10 30 atoms 
1 mole
192.22 g

 7.34  10 8 g
23
1 mole
6.02  10 molecules
6) Calculate the number of moles in each of the following.
a. 0.50 g sodium bromide (NaBr)
0.50 g 
1 mole
 0.0049 mol
102.89 g
b. 13.5 g magnesium nitrate [Mg(NO3)2]
13.5 g 
1 mole
 0.091 mol
148.33 g
c. 1.02 × 1023 formula units magnesium chloride (MgCl2)
1.02  10 23 formula units 
1 mole
 0.169 mol
6.02  10 formula units
23
d. 6 molecules monochloromethane (CH3Cl)
6 molecules 
1 mole
 9.97  10 24 mol
23
6.02  10 molecules
7) What is the volume at STP of 2.66 mol of methane (CH4) gas?
2.66 mol 
22.4 L
 59.58 L
1 mol
8) Calculate the density of N2 gas at STP.
28.02 g 1 mol
g

 1.25
1 mol
22.4 L
L
9) What is the equivalent in moles of 135 L of ammonia (NH3) gas at STP?
135 L 
1 mol
 6.03 mol
22.4 L
10) What is the molarity of solution made by dissolving 10 g of NaCl into enough water
to make 250 mL of saltwater solution?
10 g NaCl
1 mol NaCl 1000 mL
mol


 0.68
or 0.68 M
250 mL solution 58.44 g NaCl
1L
L
III. Percent Composition and Chemical Formulas
11) A compound analyzed in a chemistry laboratory consists of 5.34 g of carbon, 0.42 g
of hydrogen, and 47.08 g of chlorine. What is the percent composition of this
compound?
0.42 g
5.34 g
47.08 g
%C 
 100
%H 
 100
% Cl 
 100
52.84 g
52.84 g
52.84 g
% C  10.11 %
% H  0.79 %
% Cl  89.10 %
12) Find the percent composition of each element in baking soda, NaHCO3.
% Na 
22.99 g
 100
84.01 g
% Na  27.37 %
%O
%H 
1.01 g
 100
84.01 g
% H  1.20 %
%C 
12.01 g
 100
84.01 g
% C  14.30 %
48.00 g
 100
84.01 g
% O  57.14 %
13) How many grams of aluminum are there in 25.0 g of aluminum oxide (Al2O3)?
25 g Al 2 O3 
53.96 g Al
 13.23 g Al
101.96 g Al 2 O3
14) How many grams of iron are there in 21.6 g of iron(III) oxide (Fe2O3)?
21.6 g Fe 2 O3 
111.7 g Fe
 15.11 g Fe
159.7 g Fe 2 O3
15) Determine the empirical formula of each of the following compounds from the
percent composition.
a. 7.8% carbon, 92.2% chlorine
7.8 g C 
1 mol
 0.65 mol C
12.01 g
1 mol
92.2 g Cl 
 2.60 mol Cl
35.45 g
0.65 / 0.65  1
so formula is CCl 4
2.60 / 0.65  4
b. 10.06% carbon, 0.85% hydrogen, 89.09% chlorine
1 mol
 0.84 mol C
12.01 g
0.84 / 0.84  1
1 mol
 0.84 mol H
1.01 g
0.84 / 0.84  1
10.06 g C 
0.85 g H 
89.09 g Cl 
so formula is CHCl3
1 mol
 2.51 mol Cl 2.51 / 0.84  3
35.45 g
16) Determine the molecular formula of the compound described in #15a if the molar
mass of the compound is 461.43 g/mol.
461.43 g / mol
 3 so formula is C3Cl12
153.81 g / mol