Australia's Science Forum

HELP.
Vinegar in flask, bicarb in balloon, mouth of balloon stretched over neck of flask (or soft drink bottle). Weigh. Lift balloon and let bicarb fall into flask. Whiz, fizz, reaction takes place. Note final mass. Since it is a closed system, why does it ALWAYS lose about 0.5% of the total mass during the reaction?
Porosity of balloon?- why then does it lose the mass during the reaction but not after? Tried it in a sandwich bag (no compression)- same result.

No, it is not my balance at fault- same result on 3 high quality balances.
What am I missing here?

Any likely answers?

talked to one of our chemistry teachers and she said that you have done REALLY well not to loss any more matter then that. And it is as you suspected the loss is through the porosity of balloon and the fitting at the neck of the flask is not 100 % tight. congratulation!!! barb

Hi All,

Keep in mind as well as the temperature will certainly affect this reaction.

There will be some losses due to the transfer of heat.

Possibly wait until the reaction has completely returned to the original temperature.(before any reaction had taken place), this may yield slightly closer results.

Don't forget that energy can be transferred from one form to another, and in this case heat is certainly a possibility.

Glass as we know it transfers heat through its surface well. Keep this in mind.

Robb...

OK So this is a thread from a very long time ago, so I doubt the original contributors are still labbies, but I found it when looking for other information. I just read about this conservation of mass experiment the other day so thought I'd add my 2 cents worth in case anyone else comes across this in the future. What I read was saying that it isn't actually mass loss due to the porosity of the balloon, but it is to do with the balloon now being filled with gas which actually makes the apparatus more buoyant in the surrounding air so the mass itself remains the same but the scales will show a lower weight. Interesting!

Some of these old threads are great. We are so lucky to have them.

Labbie wrote: ↑10 May 2021, 14:48 Some of these old threads are great. We are so lucky to have them.

We are! Also lucky some of us are still around from back then.