[AL]

Hello,

I am trying to precipitate Cu²⁺ out of solution using a titration method. Any suggestions on a simple/standard method to find the pH value of when the copper will precipitate and the concentrations of the materials I would need? I am working with small concentrations of Cu²⁺, in micrograms (µg).

Thank you!

[Borek]

Why titration? And what pH has to do with the process?

[AL]

is there a better method? i thought titration would be the simplest way and then i could measure pH at the endpoint.

[Borek]

PLease explain what it is that you are trying to do, what you wrote so far doesn't make much sense. My guess is that you are confusing different things.

[AL]

I think I am, too...

I am trying to find the pH at which dissolved Cu²⁺ precipitates out of solution and use a simple lab method to figure this out.

[ardbeg]

what base are you using to precipitate copper?  if you use a pH meter you can add aliquots of base and watch the pH change, it should stop changing when the Cu starts to precipitate, and then rise once all the Cu is precipitated.

[Borek]

what base are you using to precipitate copper?  if you use a pH meter you can add aliquots of base and watch the pH change, it should stop changing when the Cu starts to precipitate, and then rise once all the Cu is precipitated.

That won't work with μg amounts.

I am trying to find the pH at which dissolved Cu²⁺ precipitates out of solution and use a simple lab method to figure this out.

See above. You may try higher concentration of copper, then the moment when it starts to precipitate should be visible with naked eye.

[ardbeg]

it should work with ug amounts of NaOH - i have done experiments on the order of 1 mg which involved preparing Cu solutions of varying pH and easily observed the formation of oxyhydroxide ppts.

[Borek]

I can be wrong, but I doubt - μg is 1000 times less than mg, we are talking about 10^-6-10^-7M solution, amount of precipitate will be very small - not to mention fact that you will need pH about 3 units higher for the precipitate to form than in the case of mg solution.