[Manu786]

Any help would be appreciated

[Borek]

With a pH meter.

Are you sure you asked a correct question?

[Manu786]

Aspirin is considered to be a weak acid, can you explain why? How can you measure the exact pH?

That is the question.

[wildfyr]

Your question doesn't make sense, that is why Borek made that query. If I dissolve 10 milligrams of aspirin in 10 mL of water I get a certain pH, if I dissolve 10 milligrams in 500 mL of water I get another. If I dissolve 10 mg in 10 mL of methanol I get a third pH.

Perhaps you are referring to the pKa? That is a specific number that doesn't vary with concentration (though it does vary with solvent).

And as for why aspirin is a weak acid, well, what are the definitions for a strong acid or a weak acid, and which of these apply to aspirin?

We will not simply do your work for you, but we will help guide you there.

[DrCMS]

If I dissolve 10 milligrams of aspirin in 10 mL of water I get a certain pH, if I dissolve 10 milligrams in 500 mL of water I get another.

Yes and Yes

If I dissolve 10 mg in 10 mL of methanol I get a third pH.

NO.  If you make that solution and put a pH meter in it I agree you'll get a reading but it is not a pH as it is a non aqueous system it can not be a pH. 

[wildfyr]

Ah, youre right. I never really thought about it, pKa is universal but pH only applies to aqueous systems.