4. Compare the experimental pKa value for each unknown with the literature values reported in Question 3. Determine the probable of each unknown and enter the answers in the Data Table. Sample #3 was a sample of potassium hydrogen sulfate and Sample #4 was a sample of potassium hydrogen tartrate. 5. Write separate equations for each unknown potassium salt dissolving in water and for the ionization reaction of the weak acid anion that each of these salts contains. (See Equations 7 and 8.) KH2P04(S) + H2O → H3O+ + KHPO4(aq)-
KHSO4(S) + H2O → H30+ + KSO4(aq)-
KHC8H4O4(S) + H2O → H3O+ +KSO4(aq)-
KHC4H4O6(S) + H2O → H3O+ KC4H4O6(aq)-
2CH3CO2C6H4COOH(S) + H2O → H3O+ 2CH3CO2C6H4COO(aq)-
6. Why was it not necessary to know the exact mass of each acid sample? The mass of the acid sample was not important because it was being dissolved in water, then divided in half and then finally one half titrated, which was indicated by a color change. The mass did not matter as long as the solution was divided equally. 7. Why was it not necessary to know the exact concentration of the sodium hydroxide solution? The concentration of the NaOH was not important because the phenolphthalein made a color change to indicate the equivalence point. 8. Why was it necessary to measure the exact volume of distilled water used to dissolve the acid, as well as the exact volume of solution transferred from the beaker of the Erlenmeyer flask? The mass and concentration of the acid was not necessary to be known because the plan was to divide the solution into two equal parts. This would balance the amounts of the acid, but would only be possible if the initial volume was precise and able to be precisely divided in half.