Question

pH and Buffers IV pH of a Buffer Solution A.2019 Mass of sodium acetate, CH,COONa, g Measured pH Calculated pH buffer solution prepared with dissolved CH,COONa +8.5 mL CH,COOH (aq) 5.54 40 mL buffer + 1.0 mL of 6.0 M HCI (aq) 4/.ces 40 mL buffer + 1.0 mL of 6.0 M NaOH (aq) 5.02 Calculated pH Measured pH 5,54 deionized water 40 mL DI water +1.0 mL of 6.0 M HCI (aq) 1.C03 40 mL DI water + 1.0 mL of 6.0 M NaOH (aq) /3.54 Compare the change in pH you observed when 1.0 mL of 6.0 M HCI is added to 40 mL of the buffer versus 40 mL of water. Is there a difference, and if so, why? Do the same for your observation of the change in pH of the buffer versus the water upon the addition of 1.0 mL of 6.0M NaOH solution. REPORT SHEET 127

pH of a buffer solution

Answer 1

Solution:

A buffer solution resists the change in pH on addition of small amount of acid or base.

A) Addition of 1 mL of 6 M HCl:

Addition of 1 mL HCl in 40 mL of buffer does not change the pH because acetate ion present in buffer solution reacts with HCl and forms unionized acetic acid and therefore no significant change in pH observed.

HCl + CH3COONa = NaCl + CH3COOH

The addition of HCl in deionized water increases H+ concentration and therefore pH decreases.

B) Addition of 1mL of 6 M NaOH:

When NaOH is added in buffer solution, the acetic acid reacts with NaOH and forms water molecules hence no significant change in pH observed.

NaOH + CH3COOH = CH3COONa + H2O

When NaOH added in deionized water, it increases OH- concentration therefore increases pH of deionized water.