[HoffMan]

Hello, I need help with calculations for lab. I prepared excess NaOH and HCL solutions (unknown conc., ~0.1M). Then I standardized my NaOH solution by titrating known amounts of KHP (Potassium hydrogen phthalate)with it in the presence of phenolphthalein (indicator turns pink at pH 8.3). Then I titrate a known amount of my HCL solution (25.00 mL) with NaOH once again, also in the same indicator. How do I use this information to find out the concentration of both solutions.
 
In total I have given:
mass KHP and volume NaOH solution required to titrate to pH 8.3.

volume HCl and volume NaOH solution required to titrate to 8.3 pH

I need to find out the concentration of both solutions.

At first I just calculated  MassKHP/MolarWeight=ConcNaOH*VolumeTitrated and then use the calculated ConcNaOH in
volNaOH*concNaOH = volHCl*concHCl to find out the concentration of HCl but then I realized that since I'm titrating to 8.2-8.3 pH and not to 7 this may not work. I'm sparing you the actual numbers because there are a LOT of those.

Once I find out the concentration of the solutions I then need to titrate an unknown sample containing an undeterminate amount of Soda Ash with phenolphtalein. After this is done keep titrating the SAME solution with methyl orange.

I've done all the titrations so I have the volumes of them but am confused on the calculations: I need to determine the Na2CO3 content of the sample.

I would like someone to help explain to me how to proceed on this. This is also pretty time sensitive so I would LOVE some quick help

[Borek]

Basically: follow just a simple stoichiometry of the acid/base reactions and don't worry about pH being different from 7.00.

To delve deeper:

http://www.titrations.info/acid-base-titration-end-point-detection