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Problems - Relative Atomic Masses

Author: John Hutchinson

Problem 1 State the Law of Combining Volumes and provide an example of your own construction which demonstrates this law.
Problem 2 Explain how the Law of Combining Volumes, combined with the Atomic-Molecular Theory, leads directly to Avogadro's Hypothesis that equal volumes of gas at equal temperatures and pressure contain equal numbers of particles.
Problem 3 Use Avogadro's Hypothesis to demonstrate that oxygen gas molecules cannot be monatomic.
Problem 4 The density of water vapor at room temperature and atmospheric pressure is 0.737 g/L. Compound A is 80.0% carbon by mass, and 20.0% hydrogen. Compound B is 83.3% carbon by mass and 16.7% hydrogen. The density of gaseous Compound A is 1.227 g/L, and the density of Compound B is 2.948 g/L. Show how these data can be used to determine the molar masses of Compounds A and B, assuming that water has molecular mass 18.
Problem 5 From the results above, determine the mass of carbon in a molecule of Compound A and in a molecule of Compound B. Explain how these results indicate that a carbon atom has atomic mass 12.
Problem 6 Explain the utility of calculating the number of moles in a sample of a substance.
Problem 7 Explain how we can conclude that 28 g of nitrogen gas (N2) contains exactly as many molecules as 32 g of oxygen gas (O2), even though we cannot possibly count this number.

Last Update: 2011-02-16