General Chemistry Principles, Patterns, and Applications, 2011

6. If you constructed a manometer to measure gas pressures over the range 0.60–1.40 atm using the liquids
given in the following table, how tall a column would you need for each liquid? The density of mercury is 13.5
g/cm 3 . Based on your results, explain why mercury is still used in barometers, despite its toxicity.
Liquid Density (20°C) Column Height (m)
isopropanol 0.785
coconut oil 0.924
glycerine 1.259
A N S W E R
1. 5.4 kPa or 5.3 × 10 −2 atm; 11 kPa, 1.1 × 10 −3 atm; the same force acting on a smaller area results in a greater
pressure.
10.3 Relationships among Pressure, Temperature, Volume, and Amount
L E A R N I N G O B JE C T I V E
1. To understand the relationships among pressure, temperature, volume, and the amount
of a gas.
Early scientists explored the relationships among the pressure of a gas (P) and its temperature (T), volume (V), and
amount (n) by holding two of the four variables constant (amount and temperature, for example), varying a third
(such as pressure), and measuring the effect of the change on the fourth (in this case, volume). The history of their
discoveries provides several excellent examples of the scientific method as presented in Chapter 1 "Introduction to
Chemistry".
The Relationship between Pressure and Volume
As the pressure on a gas increases, the volume of the gas decreases because the gas particles are forced
closer together. Conversely, as the pressure on a gas decreases, the gas volume increases because the gas
particles can now move farther apart. Weather balloons get larger as they rise through the atmosphere to
regions of lower pressure because the volume of the gas has increased; that is, the atmospheric gas exerts
less pressure on the surface of the balloon, so the interior gas expands until the internal and external
pressures are equal.
Robert Boyle (1627–1691)
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