How would you prepare 1 L of a 0.100 M phosphate buffer at pH 6.90 using crystalline K2HPO4 and a solution of 1.0 M HCl? In the answer boxes below, indicate how much of each species you would add to make up the solution. Some physical constants for K2HPO4 are given in the "Hint(s)" link. Mix together grams of K2HPO4, mL of 1.0 M HCl, and L of water. Submit Answer Try Another Version 1 item attempt remaining Hint 1 of 2 There are three pka values for phosphoric acid: pkai = 2.14, pka2 = 7.20, and pka3 = 12.40. The first value is for the loss of the first proton of phosphoric acid, the second value is for the loss of a proton from dihydrogen phosphate ion, and the third value is for the loss of the last proton from hydrogen phosphate ion