I have to prepare my chemical report about CO2 molecular mass. I searched and got a sample report from internet.

I read it and I can't understand this.

Weight of flask covered with glass cover = flask+glass cover + air in it

Weight of flask uncovered with the cover+cover = flask+glass cover

Why the report says there is difference? I thought there is no difference..

Make a pin hole to covered flask, then does its weight suddenly decrease?

And I also want to know how buoyancy works in that case.

I'm not good at english so I think I didn't write what I exactly want to ask. But if you answer me, I'll be very happy. :)

  • $\begingroup$ Your right it makes no sense. Maybe the lid stops CO2 from escaping? Maybe there was a hot match in the flask? $\endgroup$ – PhysicsDave Mar 9 '19 at 0:11
  • $\begingroup$ @PhysicsDave Only air was in it. measure the weight of air was the purpose. Thanks for answering me $\endgroup$ – milkyquartz Mar 9 '19 at 0:15
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    $\begingroup$ Not clear what you are asking. You need to describe the experiment, or post a copy of the report. $\endgroup$ – sammy gerbil Mar 9 '19 at 1:11
  • $\begingroup$ The report is wrong $\endgroup$ – Alchimista Mar 9 '19 at 8:50

Obviously it's wrong to say an uncovered flask weigh less than the covered unless the covered is either pressurized or the uncovered pushes out the air somehow when placed on the weight meter. Buoyancy force by Archimedes principle is the weight of the fluid displaced by the volume of the object immersed in the fluid. $$F_B=\rho gV$$

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