Question

Procedure :

Note : During the lab, look for a qualitative observation that proves CO2(g) is denser than air.

(1)Weigh the empty 400mL Erlenmeyer flask with a rubber stopper on.

(2)Obtain few small pieces of CO2(s) in the flask. The total amount should be close to the given rubber stopper in size. Let it sublime. Make sure the pieces are small enough so you can see them ‘sing’ and ‘dance’.

* Should you have your rubber stopper on or off during the sublimation? Why?

(3) When sublimation is done, cap it with the stopper and weigh it. We are assuming that the container is completely filled with CO2 at this point.

* How can you be sure that there is no air left in the flask?

            * What does this mass contain?

Answer 1

In Second part we should remain the container open or without stopper because when the sublimation process started the volume of the CO2 got expand or increase so that the air present in the container got displaced by the CO2 gas and the air got totally removed from the flask after some period of time.

Yes since CO2 is denser than the air the gas generate during sublimation displaces the air present above in the flask so as the CO2 solid got converted into CO2 gas the whole air got removed from the container.

Now to calculate the mass of CO2 , Since the stopper was placed after the sublimation process has done so there will be no increase in pressure in the flask. So the pressure in the flask is atmospheric pressure and we assume temperature as standard 25 degree Celcius. And Given volume is 400 ml. So from ideal gas equation

No. of moles n

therefore mass of the CO2 present in the flask