Hosphoric acid is a triprotic acid ( K a1 = 6.9 × 10 − 3 Ka1=6.9×10−3 , K a2 = 6.2 × 10 − 8 Ka2=6.2×10−8 , and K a3 = 4.8 × 10 − 13 Ka3=4.8×10−13 ). To find the pH of a buffer composed of H 2 PO − 4 ( aq ) H2PO4−(aq) and HPO 2 − 4 ( aq ) HPO42−(aq) , which p K a Ka value should be used in the Henderson–Hasselbalch equation? p K a1 Ka1 = 2.16 p K a2 Ka2 = 7.21 p K a3 Ka3 = 12.32 Calculate the pH of a buffer solution obtained by dissolving 15.0 15.0 g of KH 2 PO 4 ( s ) KH2PO4(s) and 31.0 31.0 g of Na 2 HPO 4 ( s ) Na2HPO4(s) in water and then diluting to 1.00 L. p H = pH=

the correct answer is b. a strong acid completely dissociates to its ions when dissolved in water. completely dissociates to and ions. a is incorrect because does not fully ionize to and ions and some remain as the compound . c and d are incorrect because, and do not fall into the category of bronsted lowry acids. a bronsted lowry acid is a proton donor and since both molecules do not have a proton to donate they are not bronsted lowry acids. likewise,   if we use the lewis acid definition, they cannot be acids. a lewis acid is an electron pair acceptor. both and have a complete octet so can not accept any electrons which disqualifies them as acids.