Lab Manual- Chapter 12

Flashcard maker : Lily Taylor
Objective
To measure the physical properties of pressure, volume, and temperature for a gaseous substance
To determine the molar mass (molecular weight) of a volatile liquid.
Osmometer
An instrument that changes in osmotic pressure of the solvent in which a substance, the solute, is soluble.
Mass Spectrometry
An instrumental method of identifying a gaseous ion according to its mass and charge.
Volatile Liquids
Readily vaporizable. These are substances with low boiling points and relatively low molarmasses.
The Dumas method of analysis can provide a fairly accurate determination of molar mass.
Number of Moles of vaporized Liquid
n(vapor) = PV/RT = (Pressure in atm x Volume in L)/ ((.08206L * atm/mol * K) * Temperature in Kelvin)

R is universal gas constant
P is the barometric pressure in atmosphere
V is the volume in liters of the vessel in which the liquid is vaporized and T is the temperature in kelvins of the vapor.

Overview
Liquid is vaporized into a fixed volume vessel at a measured temperature and barometric pressure.

A boiling water bath of measured temperature is used to vaporize an unknown liquid. The volume of the flask is measured by filling the flask with water, when open to atm, measure pressure.

This will determine the molar mass of the low boiling point liquid.

The mass of the vapor (m vapor)
Determined from the bass difference between the empty vessel and the vapor-filled vessel.

M(vapor) = m (flask + vapor) – m (flask)

The molar mass of the compound (m compound)
Mvapor/Nvapor
Van der Waals
A modification to the ideal gas law that can be used to correct for the intermolecular forces and molecular volumes in determining the moles of gas present in the system.

(P+ n²a/V²)(V-nb) = nRT
PVTR have the same meanings as other equation.
A is the experimental value that represents the intermolecular fores of the vapor
B is the experimental value that is representative of the volume of the molecules.

How is the pressure of the vaporized liquid determined in this experiment?
The atmospheric pressure (use a barometer)
How is the volume of the vaporized liquid determined in this experiment?
The volume of the liquid is the volume of the flask
How is the temperature of the vaporized liquid determined in this experiment?
The temperature of the vaporized liquid is cooled to temperature
How is the mass of the vaporized liquid determined in this experiment?
The mass of the vaporized liquid is the mass of the vapor and flask minus the mass of the flask.
The ideal gas law equation is an equation used for analyzing ideal gases. According to kinetic molecular theory that defines an ideal gas, no real ones exist. Van der Waals’ equation is an attempt to make corrections to real gases that do not exhibit ideal behavior. Describe the type of gaseous molecules that are most susceptible to nonideal behavior
The size of the particles and they have intermolecular forces that differentiate the behavior.
Chart
The mass of the flask (before the sample is placed into the flask) is measured when the outside of the flask is wet. However, in Part B.3 the outside o the flask is dried before its mass is measured.
Will the mass of the vapor in the flask be reported as too high, or too low?
Will the molar mass of vapor in the flask be reported as too high or too low?
It would be too high because the waters weight would be mistaken for the mass of the vapor. IF the mass of the water vapor is reported as being too high, than the reported molar mass will be too high.
From the time the mass of the flask is first measured in Part A.1 until the time it is finally measured in Part B.3, the outside of the flask is handled with oily fingers. Does this lack of proper technique result in the molar mass of the vapor in the flask being reported as too high, too low?
The molar mass of the vapor will be considered too high because the mass of the oil will be factored in as weight from the vapor.
The aluminum foil is pierced several times with large pencil sized holes instead of pin sied. How will this oversight in the procedure affect the mass of of vapor?
Will the reported molar mass of the liquid be reported as to low or too high?
The mass of vapors would be too low because the chunk of water vapor will escape, this decrease will diminish the reported amount.
If the mass of the water vapor is too low than the reported mass will also be too low.
The flask is completely filled with vapor only when it is removed from the hot water bath in part B.3. However, when the flask cools, some of the vapor condenses in the flask. As a result of this observation, will the reported molar mass of the liquid be too high or too low?
Suppose the thermometer is miscalibrated to read .3C higher than actual. Does this error in calibrations result in the molar mass of the vapor in the flask being reported as too high or too low?
If the volume of the flask is assumed to be 125 mL instead of the measured volume, would the calculated molar mass of the unknown liquid be too high, too low, or unaffected?
The pressure reading from the barometer is recorded higher than it actually is. How does this affect the molar mass of the liquid: too high or too low

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