Analysis:
- Calculate the molecular mass of the unknown. What possible sources of error were not ac-
counted for in the calculations?
.
(./ )..
..
MM PV
gRT
mol K atm Lg L atm K
g mol0
750 760 0 264 50 60 430 0 0821 373 5 1
:::
:::::::
== =: -Possible sources of error might include:
(a) mass of air
(b) thermometer immersion point
(c) diffusion effects (air/vapor)
(d) the B.P. of the water at 100.5°C at 750. torr would indicate either a faulty thermome-
ter or that she was using tap water with an ionic concentration of approximately 1m.
Calibrations factored in the analysis for the thermometer or correctional factors for
the type of water could have been made.- Explain how the following errors would affect the calculated molecular mass:
(a) She removed the flask prematurely from the hot water bath leaving some of the un-
known in the liquid phase.
The mass of the condensate would be larger than expected, since it would include the
mass of the vapor and the mass of the liquid. MM would be higher than expected.
(b) She did not dry off the flask properly and left a few drops of water on the outside of
the flask.
The mass of the condensate would be larger than expected, since it would include the
mass of the vapor and the mass of the drops of water. MM would be higher than
expected.
(c) She was not careful to keep the aluminum foil on the flask while it was cooling.
The calculated mass of vapor would be smaller than expected, since some of the va-
por would have escaped from the flask prior to the flask being weighed. MM would
be too small.
(d) She removed the flask too soon from the boiling water bath, not allowing it a chance
to reach the temperature of the hot water.Since the temperature of the water bath did not equal the temperature of the vapor,
the temperature value used would be too large since the sample was collected at a
lower temperature than the boiling water. MM would be too large.Part III: AP Chemistry Laboratory Experiments