You plan to make a buffer solution to study blood cells, which require an environment where the pH is around 7.40. Which of the following mixtures will make the best buffer for your purpose? Find Ka values in your acid-base lecture notes.
0.001 M $H_2PO_4^-$ and 0.001 M $HPO_4^{2-}$
0.1 M $H_3PO_4$ and 0.1 M $H_2PO_4^-$
0.001 M $HPO_4^{2-}$ and 0.001 M $PO_4^{3-}$
0.1 M $H_2PO_4^-$ and 0.1 M $HPO_4^{2-}$
