In this week\'s experiment you will determine the molar mass of carbon dioxide b

Question

In this week's experiment you will determine the molar mass of carbon dioxide by measuring the mass of an Erlenmeyer flask full of the gas. The following calculations are intended to familiarize you with the general procedure:

The mass of an empty Erlenmeyer flask and stopper was determined to be 40.07 grams. When filled with distilled water, the mass was 303.6 grams. The atmospheric pressure was measured to be 0.9582 atm, the room temperature was 19.00oC. At this temperature, the vapor pressure of water is 16.50 torr -- but assume a 50% relative humidity as outlined in the procedure for this experiment.

What is the number of moles of air in the flask?

Moles of air in the flask = mol

If the average molar mass of the gases present in air is 28.960 g mol-1, what is the mass of air in the flask?

Mass of air in the flask = grams

What would be the mass of carbon dioxide in the flask?

Mass of carbon dioxide = grams

What would be the mass of the flask (and stopper) when filled with carbon dioxide gas? In this case the CO2 will be saturated with water vapor so assume 100% humidity as outlined in the experiment.

Mass of flask and stopper filled with CO2 gas = grams

Explanation / Answer

volume of flask..
(303.6g - 40.70g) x (1mL / 1g) = 262.9mL

moles air..
PV = nRT
n = PV/(RT) = (0.9582atm) x (0.262L) / ((0.08206 Latm/molK)x(292.15K))
n = 0.01040 moles

mass air in flask..
0.01040 mol air x (28.960g air / mol air) = 0.303g

mass CO2.. note!.. moles CO2 = moles air!
0.01040 mol CO2 x (44.01g CO2 / mol CO2) = 0.4577g

mass (flask + stopper) - mass (air)..
40.70g - 0.303g = 40.397g

mass (flask + stopper) + mass (CO2)...
40.397g + 0.4577g =40.8547g

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