## Chemistry (7th Edition)

(b) $H_2P{O_4}^-$ and $H{PO_4}^{2-}$ This pair is the best choice because the $pKa$ for its acid "$H_2P{O_4}^-$" is the closest to 7.00.
Calculate the $pK_a$ for each acid pairs: (a) $pKa = -log(Ka)$ $pKa = -log( 7.5 \times 10^{- 3})$ $pKa = 2.13$ (b) $pKa = -log( 6.2 \times 10^{- 8})$ $pKa = 7.21$ (c) $pKa = -log( 4.8 \times 10^{- 13})$ $pKa = 12.32$ ** You can find these values in the page 1045 of this book. Identify the closest to the wanted pH (7.00) - It is the (b) pair.