The dissociation constant of a weak acid is 1×10-4. In order to prepare a buffer solution with a pH=5, the [Salt]/[Acid] ratio should be
pH=pKa+log[ Salt ][Acid] 5=-logKa+log[ Salt ][ Acid ] ∵pKa=-logKa 5=-log1×10-4+log[ Salt ][ Acid ] 5=4+log[ Salt ][ Acid ] 5-4=log[ Salt ][ Acid ] 1=log[ Salt ][ Acid ] [ Salt ] [Acid] =10=10:1