[appleseed]

When you have a sample of CH3COOH, you get a very strong acidic smell.

I'd just like to know what this means??

I've heard that some organic acids decompose in air. But to my understanding, the reason why I can smell the acid is because the intermolecular forces are weak and the acid particles break free into the air so you can smell it.

BUT IF THE ACID REACTS WITH OXYGEN, Does this mean that if an acid was placed in open air for a long time, the concentration would change and results would be innacurate if it was used in an experiment?

Thank you!!

[Yggdrasil]

When you have a sample of CH3COOH, you get a very strong acidic smell.

I'd just like to know what this means??

I've heard that some organic acids decompose in air. But to my understanding, the reason why I can smell the acid is because the intermolecular forces are weak and the acid particles break free into the air so you can smell it.

Correct.  Small quantities of the acid will evaporate from solution into the air where you can smell them.  This has nothing to do with any chemical change affecting the acid.  It is just a simple evaporation.

BUT IF THE ACID REACTS WITH OXYGEN, Does this mean that if an acid was placed in open air for a long time, the concentration would change and results would be innacurate if it was used in an experiment?

Thank you!!

Evaporation is not a reaction with oxygen, but your are correct: if you leave a sample of acetic acid (or any other solution) out in an open container for a long period of time, evaporation of the volitile components will alter the concentrations of the solution (also, if you have glacial acetic acid, you will have problems with moisture from the air getting into your solution).  These changes will be fairly small, but if you need to know the concentration very accurately, it could affect your results.  In the case of acetic acid, I would not worry about reactions with oxygen causing decomposition of the solution, however.