1. Briefly explain why it was not necessary for you to determine the mass of unk

Question

1. Briefly explain why it was not necessary for you to determine the mass of unknown liquid that you transferred to the flask before heating.


2. Would the molar mass of a volatile liquid, calculated using the procedure in this experiment, be incorrectly high, incorrectly low, or unaffected by the following procedural changes?

(a) You did not completely vaporize the liquid when you heated it.

(b) The foil cap got wet while you were cooling the flask and its contents with running water.

(c) You added the boiling stone to the flask after you had already determined the mass of the empty flask and foil cap.

(d) You forgot to measure the volume of the flask, so you used the volume printed on the flask for your calculations.

(e) Your unknown liquid had a boiling point of 102.3 Celsius.

3. The density of air at 100.0 deg. Celcius is less than 1.00g L^-1. Is it reasonable to assume that the vaporized liquid will force all of the air from the flask during heating? Briefly explain.

Any part of the question answered will be greatly appreciated! :)

Explanation / Answer

1)

because, as you heat this gas, you are creating a vapor and the vapor must be sufficient enough to drive out the air in the tube so that you only have the vapor of the liquid present in the tube. as long as you see teh vapor leaving the tube, through the pin hole, and notice when it stops, the test tube will contain only the vapor that you require to calculate the molar mass.

2)

In the Dumas method a volatile liquid is heated to a known temperature (above its boiling point)
and allowed to escape from a container through a tiny orifice. Once the liquid has vaporized, the
container is cooled to room temperature. Gradually the vapor which remained in the container at the
higher temperature condenses to a liquid and is then massed. If the volume of the container is known
along with the high temperature, the room pressure can be used (because the system is open to the
atmosphere through the orifice) to calculate moles. From there a molar mass can be determined.

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