Question

Argon gas is collected over water at 18C and 738 torr. What mass of argon gas would
be present in a 500.00 ml sample of this gas? The vapor pressure of water at 18C is
15.9 torr.

Answer 1

Answer:

Problem:

193 mL of O2 was collected over water on a day when the atmospheric pressure was 762 mmHg. The temperature of the water was 23.0 o C. How many grams of oxygen were collected?

Strategy:

Use Dalton's law and the vapor pressure of water at 23.0 o C to correct the pressure to units of atmoshperes.

PT = Poxygen +Pwater

At 23.0 o C the vapor pressure of water is 21.1 mmHg. (This can be found on a vapor pressure table.)

762 mmHg = Poxygen + 21.1 mmHg

Poxygen = 762 mmHg - 21.1 mmHg

Poxygen =741 mmHg

Convert the corrected pressure to atmospheres.

(741 mmHg) (1 atm / 760 mmHg) = 0.975 atm

Use the ideal gas law to find out how many moles of gas were produced:

PV = nRT (remember to put volume in liters and temperature in Kelvin)

(0.975 atm) (.193 L) = n (.0821 L atm / mol K) (298 K)

n = (0.975 atm) (.193 L) / (.0821 L atm / mol K) (298 K)

n = 7.69 X 10-4 mol