[elwplw]

I'm feeling really stupid right now, because I'm supposed to know how to do this myself, but it's been so long ago since I last worked with this type of calculation.

I have 0.050 M Triton X-100, lets say 1ml of it (I haven't decided the quantity I want to use yet). I have to my disposal HCl and NaOH of the following concentrations: 1M, 0.1M and 0.01M

I want to add minute quantities of the acid and/or base, to adjust the pH of my Triton solution to 3, 7.12, and 11 (and some other concentrations, but I'll figure the rest out myself with a little help here). I do not want to use a pH meter to just randomly add and hope it comes out right - I want to basically know what volume I need to add to get these pH values. That's to say, I want the solution at pH 3, then adjust the pH (in the same(!) solution) to 7.12 and 11 by adding acid/base (to the same (!) solution). The volume added should be small enough to be neglected. 

Help, please ?!

[Borek]

Assuming Triton doesn't react with acids and bases, pH 3 means just 0.001M HCl. To go up to 7.12 in the same sample will be tricky, although it can be done with addition of sodium carbonate (you will create buffer). Finally some NaOH would push it up to 11.

[elwplw]

Thanks for the help.

It's not indicated that I should use any sodium carbonate - the instructions I've been given is that I'm supposed to adjust the pH using only the acid and base mentioned previously. But I've been "experimenting" with a theory here. Can I consider my system as a strong acid-base "titration", in which I know the pH target, but am looking for the volume of base to add ? So, if I want to change my pH from 3 to 5, I could work backwards in the calculations, from pH 5 = concentration of H3O+ left in my solution after the reaction with [the added] OH- => quantity of OH- needed to react with the amount of H3O+ present in my solution at pH 3, and thus volume (from some appropriate choice out of the concentrations available) required ?

Don't know if this made sense...?

Also, having completely forgotten all my knowledge regarding acids and bases, am I supposed to take the autoprotolysis of water into consideration at any stage in any of my calculations ? Don't know why I should, but only remember that it used to create problems for me years ago when I forgot it when it came to dilute acid/base solutions (so thought I'd be on the safe side and ask ).

[Borek]

Titration idea is not bad, but close to pH 7 microliters will give a huge pH changes, aiming at 7.12 is completely unrealistic.

Close to 7 water autodissociation has to be taken into account.

If you need more please check these pages:

http://www.chembuddy.com/?left=pH-calculation&right=toc

http://www.titrations.info/acid-base-titration-curve-calculation
http://www.titrations.info/acid-base-titration-end-point-detection (take a look at tables - small volumes give huge pH changes)

Check also programs linked to in my signature - BATE and Buffer Maker are both designed for pH calculations. While neither works in "give volumes for a given pH" mode, using them for finding volumes by trial and estimate is very fast.

[elwplw]

Thank you very much for the links, they were exactly what I needed !