What is the mass of air in a 250-mL Erlenmeyer flask (actual volume is 267
mL) at a typical laboratory pressure of 715 torr and a temperature of 21˚C?
Assume air to be an ideal gas having an average molar mass of 29.0 g/mol.
To determine the mass of air in the Erlenmeyer flask, we can use the ideal gas law equation: PV = nRT, where P represents pressure, V represents volume, n represents the number of moles, R is the ideal gas constant, and T is the temperature.
First, we need to convert the given volume of the Erlenmeyer flask from mL to liters:
Volume = 250 mL = 250/1000 = 0.25 L
Now, we can convert the pressure from torr to atm:
Pressure = 715 torr = 715/760 = 0.9408 atm
Next, we convert the temperature from ˚C to Kelvin:
Temperature = 21˚C + 273.15 = 294.15 K
The ideal gas equation becomes:
(0.9408 atm)(0.25 L) = n(0.0821 L.atm/mol.K)(294.15 K)
Rearranging the equation to solve for n (number of moles):
n = (0.9408 atm * 0.25 L) / (0.0821 L.atm/mol.K * 294.15 K)
Now we can calculate the number of moles:
n = 0.0093447 moles
Finally, we can calculate the mass of air using the molar mass given:
Mass = number of moles * molar mass
Mass = 0.0093447 moles * 29.0 g/mol
Calculating the mass:
Mass = 0.2702 g
Therefore, the mass of air in the 250-mL Erlenmeyer flask is approximately 0.2702 grams.
To calculate the mass of air in the Erlenmeyer flask, we can use the Ideal Gas Law equation:
PV = nRT
Where:
P = Pressure of the gas (in atmospheres or torr)
V = Volume of the gas (in liters or milliliters)
n = Number of moles of gas
R = Ideal gas constant (0.0821 L.atm/mol.K)
T = Temperature of the gas (in Kelvin)
First, we need to convert the given volume from mL to L:
V = 250 mL * (1 L / 1000 mL) = 0.250 L
Next, we convert the pressure from torr to atm:
P = 715 torr * (1 atm / 760 torr) = 0.940 atm
Now we need to convert the temperature from °C to Kelvin:
T = 21°C + 273.15 = 294.15 K
We are given that the average molar mass of air is 29.0 g/mol, so the molar mass will be used as the numerator in the molar mass-to-mass conversion factor.
Next, we need to find the number of moles of air using the Ideal Gas Law equation:
PV = nRT
Rearranging the equation to solve for n:
n = PV / RT
Substituting the given values:
n = (0.940 atm) * (0.250 L) / [(0.0821 L.atm/mol.K) * (294.15 K)]
Calculating n:
n ≈ 0.0100 mol
Finally, we can find the mass of air using the molar mass of air:
Mass of air = n * molar mass
Mass of air = (0.0100 mol) * (29.0 g/mol)
Calculating the mass of air:
Mass of air ≈ 0.290 g
Therefore, the mass of air in the 250-mL Erlenmeyer flask at a temperature of 21˚C and a pressure of 715 torr is approximately 0.290 grams.
Use PV = nRT and solve for n.
Then n = grams/molar mass.
You know n and molar mass, solve for grams.