Introductory Chemistry

Quiz: Gas laws; measuring pressure

Cracolice 2/e Ch 4 & 13.

Answer key
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Quiz is "closed book" except for PT & calculator.
Show clear work for all calculations. Use proper SF.

R = 0.0821 L.atm/(mol.Kelvin). Molar volume of an ideal gas at STP = 22.4 L. STP = 0° C, 1 atm (= 760 mm Hg = 760 torr). Density of Hg = 13.6 g/mL.

1. You have a 1.00 L bottle of gas, with P = 0.444 atm and T = 295° C.

a. You raise the temperature to 395° C...

* Without doing any calculations, qualitatively predict whether the pressure will rise or fall. Explain.

* Now calculate the new pressure.

b. Calculate how many moles of gas are in the bottle.

c. Is your answer for part b "reasonable"? There are probably many ways to approach this, but I will start you on one... If the conditions were STP, approximately how many moles would you expect? Then, make some adjustments for the conditions. (The purpose of the question is to help you visualize the situation, rather than simply rely on a formula.)

d. What gas does this question apply to? (That is, what gas would your calculations apply to?) Explain.

2. Sketch a manometer (U-tube), open to the atmosphere at one end and connected to a container of gas at 780 mm Hg at the other. Show how you would read the pressure.

3. Recall that the idea of a manometer is that a column of Hg(l) 760 mm high exerts the same pressure as a column of air extending from the surface of the earth to the top of the atmosphere (that is, an "atmosphere" of air).

a. If we wanted to use water in a manometer, how much water would we need? That is, how many mm water = 1 atm?

b. Why do we use Hg in ordinary manometers and barometers?


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Last update: August 13, 2011