3. Using the measured pH and the appropriate [HPO?] / [H2PO4] ratio for each of your buffers, substitute into the K'expression and obtain a value for the apparent pk', of phosphate. Organize your data in a table containing expected pH, observed pH, (H"). [HPO ] / [H2PO4], K'. (apparent), pk'a (apparent). How does your average apparent pk's compare with 6.75, a typically accepted value for this constant? Explain your results, and show your calculations. 4. Using the average pk's value calculated in 3, calculate the pH of the pH 7.0 buffer solution that is expected after the addition of 1.0 mL of 1.0 M HCl and 1.0 mL of 1.0 M NaOH. How do these calculated pHs compare to the actual measured pHs after the addition of the Hi or OH? Explain your results and show your calculations. Actual Volumes pH's after Ht Buffer # Target pH H2PO4 HPO42- H2O Actual after OH 1 6.0 47.1 2.95 50.0 5.78 3.21 6.31 2 2 6.5 41.7 8.31 50.0 5.68 5.68 6.77 3 7.0 30.7 19.34 50.0 6.43 6.43 7.14 4 7.5 16.5 33.61 50.0 6.94 6.94 4.45 5 8.0 6.9 43.14 50.0 7.25 7.25 8.23