Uses of the Ideal Gas Equation:
I.
Solving for Molecular Mass of an unknown gas (Butane Lighter Lab)
n = number of moles (units: mol)
m = mass (units: grams)
M = molecular mass (units: grams/mol)
Note: M = m
n
therefore
n=m
M

PV = nRT
PV = mRT
M
Example: Solve for molecular mass (M) given m = 0.800 g, P = 106.7 kPa, T = 100°C, V =
0.372 L, R = 8.31 L∙kPa
mol∙K
II.
Gas Stoichiometry
A +
1)
2)
3)
4)
5)
6)
7)
B

C
+
D
VV
Mass  V
V  Mass
Mass  Density
Density  Volume
Limiting Reactants
Mass  Molecular Mass
1
Example 1: Volume to Volume Stoichiometry Gas Law Problem
What volume of gas is produced from x liters substance?
How many liters of hydrogen chloride gas will be produced from 2.00 L hydrogen gas?
H2 (g) + Cl2(g)  2 HCl (g)
2.00 L
?? L
Example 2: Mass to Volume Stoichiometry Gas Law Problem
What volume of gas is produced from x grams substance?
Steps:
1. Balance equation and compound formulas
2. Find moles
3. Find mole ratio
4. Convert moles gas  volume of gas (1 mol = 22.4 L)
How many liters of hydrogen gas will be produced from 6.54 g of zinc?
2 HCl (aq) + Zn (s)  H2 (g) + ZnCl2 (aq)
6.54 g
?? L
Example 3: Volume to Mass Stoichiometry Gas Law Problem
What mass of gas is produced from x liters substance?
What mass of magnesium will react with excess sulfuric acid to produce 500 mL of
hydrogen?
Mg
?? g
+
H2SO4

H2 +
MgSO4
500 mL
2
III.
Determining Gas Density
Step 1: Start with PV = mRT and solve for the molecular mass (M).
M
Step 2: Density (D) is mass (m) per unit volume (V).
Write in equation form: ________________
Step 3: You can introduce the density equation into the equation from step 1. Find m in M =
mRT equation from step 1. Replace m with D.
PV
V
Step 4: Solve for density (D).
Example 1: Calculate the density of sulfur dioxide at STP to 3 significant figures. (hint: from
balloon worksheet) (Ans: 2.87 g/L)
Example 2: What is the density of a sample of ammonia gas, NH3, if the pressure is 0.928 atm
and the temperature is 63.0°C?
(Ans: 0.527 g/L)
3
Molar Volume Problem
Example 11-2
A reaction yields 98.0 ml of SO2 gas at STP. What is the mass (g) of the gas produced?
Answer: 0.280 g SO2
0.098 L 1.0 mol SO2
22.4 L
64.1 g SO2 = 0.280 g SO2
1 mol SO2
(Ex. 2) 4.37 g of a diatomic gas occupies a volume of 3.00 L at 1.00 atm and T=45oC.
What is the gas?
F2
4