[kaihou]

I got a lab to determine the molar mass of butane by using experimental data and a bunch of equations. We had to to the following steps in the procedure:

1. Fill a bowl partially with water
2. Fill a conical flask to the brim with water
3. Flip the flask upside-down into the bowl of water without letting any water escape
4. Attach a tube from a butane lighter and the upside-down conical flask
5. Displace the water in the flask with butane gas
6. Raise or lower the flask until the water levels inside and outside were equal

That's all you basically need to know for now. Our group didn't do step number 6, and one of the questions on the worksheet is:
"Why is it necessary to raise or lower the cylinder until the water levels inside and outside are equal?"

I sincerely have no clue as to why . Any help whatsoever would be great. Thanks in advance!

[ARGOS++]

Dear kaihou;

Think about the pressure in the flask in case the water-level is different inside the flask from outside! 
You may also use the ideal gas-law for understanding what this means to the real volume.

I hope to have been of help to you.
Good Luck!
                    ARGOS⁺⁺

[kaihou]

Oh wow, I can't believe I didn't even come close to thinking about the pressure. Duh!

Thanks so much, it really helps!

[ARGOS++]

Dear kaihou;

You 're welcome!   ─   Soon again.

Good Luck!
                    ARGOS⁺⁺

 P.S.: Thank you too!
.