Question

C. pH of Buffer Solutions (continued): Measured pH Calculated pH (from [H+] in previous table) C.1 Buffer C.2a Buffer + HCI 4.82 4.45 4.96 S.S7 C.2b Buffer + NaOH C.3 Water C.4a Water + HCI C.4b Water + NaOH 12.34 Compare and explain the difference in pH change occurring for the buffer system and for the water on the addition of HCl.

Answer 1

Buffer is a system which resist the change in pH when small amount of acid and base are added

Buffer mainly contain an acidic part (weak acid) and basic part (strong conjugate basic salt)

so as we see pH of buffer initially is 4.82

on adding HCl since it is a strong acid it dissociates completely to give H+ ion which may change the pH

but since buffer has a basic unit (strong conjugate basic salt) it react with all H+ to form weak acid which dissociates ver less due to common ion effect hence change is pH is very small (4.45)

Similar explanation can be given if we add NaOH it reacts with the acid part to give salt which neutralizes all the OH- hence here also pH changes by small amount

But in case of water since initial pH is 5.57 hence on adding HCl or NaOH there is a large amount of H+ and OH- in the water which changes the pH drastically as evident by the measured pH

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