In this experiment we assume that: A) At the instant before the flask is removed

Question

In this experiment we assume that:
A) At the instant before the flask is removed from the boiling water bath, the flask is completely filled with vapor only and vapor is at the temperature of the water bath.

B) After cooling, the flask contains only the condensed liquid plus air at room temperature.

C) The pressure inside the flask is always equal to the atmospheric pressure outside the flask.

1) How would the observed molar mass of the unknown liquid have been affected by the following circumstances (would it be higher than the true value, lower than the true value, or remain unchanged and why).

a)Because some portion of the neck of the flask was above the hot water level, not all the vapor in the flask was the same temperature.

b) Some of the liquid had not yet vaporized when the flask was removed from the bath.

c) While the flask was cooling, some of the vapor effused through the foil pinhole in the cap.

Explanation / Answer

a) Remain unchanged. As long as the temperature is enough to vaporize the liquid, it would displace the air inside the flask. Also, the vaporization occurs in the lower portion of the flask (where the liquid is).

b) Higher. The liquid is heavier than the vapor. So if liquid is occupying volume that should be occupied by the vapor, the overall weight is going to be higher than if only vapor was present.

c) Lower. Because some vapor escaped before being condensed, the liquid present in the flask after condensation will not be the complete volume of the flask.

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