There are many ways for making a phosphate buffer. Depending on what is available in the lab, a phosphate buffer can be made from (i) phosphoric acid and a strong base, eg. H3PO4 / NaOH; (ii) a phosphate salt and the addition of either a strong acid or base, eg. NaH2PO4 / NaOH; (iii) the phosphate salt of both the conjugate acid and the conjugate base, eg. NaH2PO4 /Na2HPO4.; or (iv) or a combination of the reagents mentioned above. More often, we start with a solution of the salt form and then titrate (with a disposable pipette) with either a strong base or acid to obtain the pH that we desire. Determine the expected pH and the buffer concentration of the following solutions (Use the Henderson-Hasselbalch equation and the pKa values as presented in the introduction to help you and show your reasoning and calculations). Provide answers with 3 significant digits. (a) 4.50 mL of H3PO4 (density = 1.88 g/mL and MW = 98.0 g/mol) added to 500 mL of water and 24.0 mL of 6.00 M NaOH. (b) 6.39 g of Na2HPO4 (MW 142 g/mol), 8.00 mL of 4.00 M HCl and enough water to make a final volume of 250 mL (c) 3.00 g of NaH2PO4 (MW 120 g/mol) and 10.0 g Na2HPO4 (MW 142 g/mol) dissolved in a total volume of 500 mL of water.