Worksheet 1.5
Supplemental Instruction
Iowa State University
Leader: Lea
Course: Chem 177
Instructor: Dr. Schewe-Miller
Date: 2/3/2013
1. Define the following terms:
-Molecular Weight: Mass of the collection of atoms represented by the chemical formula for
a molecule
-Formula Weight: Mass of the collection of atoms represented by a chemical formula
-Atomic Weight; Average mass of the atoms of an element in amu, equal to the mass in
grams of one mole of the element
-Atomic Mass: The exact mass of a specific isotope of an element
2. Calculate percent composition for each of the elements in the following compounds:
a. NH3
N_____ H_____
1(14.01) + 3(1.01) = 17.04
N = 1(14.01)/17.04 * 100 = 82%
H = 100-82 = 18%
b. C6H12O6
C_____ H_____ O_____
6(12.01) + 12(1.01) + 6(15.9994) = 180.14
C = 6(12.01)/180.14 * 100 = 40%
H = 12(1.01)/180.14 * 100 = 6.7%
O = 100-6.7-40 = 53.3%
c. H2SO4
H______ S_____ O_____
2(1.01) + (32.065) + 4(15.994) = 98.085
H = 2(1.01)/98.085 * 100 = 2%
S = 32.065/98.085 * 100 = 32.7%
O = 100 - 2 - 32.7 = 65.3%
d. CCl4
C______ CL______
12.01 + 4(35.435) = 153.822
C = 12.01/153.822 * 100 = 7.81%
Cl = 100-7.81 = 92.19%
3. Stoichiometry
a. If you have 36g of He, how many moles of He do you have?
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36g * 1 mol/4.001 g = 9.0 mol He
b. What is the mass (in grams) of 1.77 moles of C2H5O?
2(12.01) + 5(1.01) + 15.994 = 45.064
1.77 mol * 45.046 g/1 mol = 79.8g
c. How many moles of hydrogen are there in 40g of water?
40g * 1 mol H2O/ 18g H20 * 2 mol H/1 mol H20 = 4.44 mol H
d. If you completely react 3.45 moles of hydrogen with an unknown amount of sulfur, how many
grams of H2S will you end up with?
3.45 mol H * 1 mol H2S/2 mol H * 34.085g H2S/1 mol H2S = 58.8g H2S