Gas Laws and Empirical Formulas Test Review Answers
In order to receive full credit, you must show all appropriate work, including units and sig figs
for each problem.
Objectives:
To be successful on this test you need to be able to do the following:
1. Calculate the percent composition of a compound.
2. Use masses or percent composition to calculate the empirical formula of a compound.
3. Use an empirical formula and molar mass to calculate the molecular formula of a
compound.
4. Use lab data to calculate the empirical formula of a hydrate.
5. Make qualitative predictions about the behavior of a gas based on the gas laws discussed
when the pressure, temperature or volume is changed.
6. Use the ideal gas law and combined gas laws to make simple quantitative predictions
concerning pressure, temperature, moles, or volume.
Practice Problems:
1. What is the percent composition of mustard gas, C4H8Cl2S? 30.20%C, 5.069%H,
44.57%Cl, 20.16%S
2. Testosterone contains 79.11%C, 9.79% H, and 11.10% O. What is the empirical formula
of testosterone? C19H28O2
3. A 3.90g sample of beta carotene (composed of hydrogen and carbon) was found to
contain 3.49g of carbon. If the molar mass of beta carotene is around 540 g/mol, what is
the molecular formula? C40H56
4. 19.1g of a hydrate of copper(II) chloride is heated strongly to produce 15.06g of
anhydrous salt. What is the formula of the hydrate? CuCl2∙2H2O
5. A sample of nitrogen gas at 18°C and 760 mmHg has a volume of 2.67mL. What is its
volume at STP? 2.5mL
6. Methanol air mixtures burn at around 1900°C and can generate a fair amount of thrust
from the expansion of the products. If a 4.0L bottle of gas at 752mmHg and room
temperature (25°C) is heated by the reaction to the flame temperature, what volume will
the gas occupy at this new temperature? 29L
7. How many moles of helium are needed to fill a 1.25L balloon at 1.1atm and 25°C?
0.056mol He