Take into account correction factors for phosphate buffers, predict the pH when 0.50ml of 1M HCl is added to 40mL of .10M buffer at expected pH 6 and pH 6.5. The buffer was made with Na2HPO4 and NaH2PO4. pKa is 7.2.
When I did this before, I got a lower pH for 6.5 than I did for 6. Which this doesn't make sense.