Part A You need to make a buffer whose pHis 70, and you can choose from the weak

Question

Part A You need to make a buffer whose pHis 70, and you can choose from the weak acids shown in table below Acid (Proton Donon Conjugate Base (Proton Acceptor) 375 1.78 x 10 +H 4.76 1.74 x 10-s CH COO Acetic acid 386 1.38 x 10 CH CH--coo CH CH-COOH HPOA. 2.14 7.24 x 10 Dihydrogen phosphate ion 686 1.38 x 10 HPOR H POA Monohydrogen phosphate ion Dhiydrogen phosphate ion PO. HPO 124 398 x 10 Monohydrogen phosphate kon 63' 5.1 x 10 Hacon 10.25 5.62 X 10 CHO 9,89 1.29 w 10 025 5.62 10 Apparent pKa and Ka values a e text Some weak acids and their conjugate bases

Explanation / Answer

to make buffer remember that pH of the buffer should be as close as possible to the pKa
pKa which is closest to 7 is 6.86 for H2PO4- and HPO42-

Hence this is the right answer

Answer:
Dihydrogen phosphate ion H2PO4- and monohydrogen phosphate ion HPO42-

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