Hey,
My AP Chem class did a lab for determing the molar mass of a volatile liquid by vapor density. There are a few calculations that I can't seem to get:
1.) The moles of air displaced by the volatile liquid vapor (at RT)
2.) The molar mass of air (calculated)
3.) Mass of air displaced by the volatile liquid vapor
What I know already is:
1.) The aparent mass of vapor that occupied the flask at the boiling water temperature
2.) the volume of the flask
3.) Moles of gas occuping the flask at the BP of water.
4.) estimated molar mass of the unknown liquid
What we did is fashion an apparatus using copper wire and aluminum foil to an Erlenmyer Flask and injected 3-4 mL of this unknown liquid and then put the flask in a beaker with water on a hot plate to evaporate the liquid and then determine the mass of the flask, apparatus, AND vapor. Thanks in advance.
I'm sorry but there just isn't enough information here for me to be helpful. Nothing about the kind of apparatus, is the Cu wire and Al foil inside or outside the flask and do they react, nothing about masses (how much of what), etc. The volume of a flask is determined sometimes by weighing the empty flask, filling with water and reweighing, then calculating the volume from the density of water.
Based on the information you provided, here are the step-by-step calculations for the three questions you have:
1. Calculation for the moles of air displaced by the volatile liquid vapor (at room temperature, RT):
To determine the moles of air displaced, you need to first find the volume of the volatile liquid vapor using the ideal gas law equation: PV = nRT, where P is the pressure, V is the volume, n is the number of moles, R is the ideal gas constant, and T is the temperature.
However, since you are dealing with air and not an ideal gas, you need to consider the partial pressure of the air. Assuming the pressure of air is the same as atmospheric pressure, you can calculate the moles of air using the following equation:
n_air = P_air * V_air / (R * T_air)
Where P_air is the pressure of air, V_air is the volume of air, R is the ideal gas constant, and T_air is the temperature of air in Kelvin.
2. Calculation for the molar mass of air (calculated):
To calculate the molar mass of air, you can use the ideal gas law equation rearranged to solve for molar mass:
Molar mass = (mRT) / (PV)
Where m is the mass of the air, R is the ideal gas constant, T is the temperature in Kelvin, P is the pressure, and V is the volume of air.
3. Calculation for the mass of air displaced by the volatile liquid vapor:
To calculate the mass of air displaced, you can use the density of air. The density of air is typically given in units of grams per liter (g/L). You can convert the volume of air displaced (which you calculated in question 1) to grams using the following equation:
Mass of air displaced = Volume of air displaced * Density of air
Please note that in order to have more accurate calculations, you need to provide more specific details and measurements of the experiment, such as the masses of the flask, apparatus, and vapor, the actual pressure, temperature, and volume measurements, and any other relevant experimental conditions.