Volume of NaOH added (mL) Titration of 40.00 mL of 0.1000 M HCI pH with 0.1000 M NaOH 147 00.00 10.00 20.00 1.00 1.22 1.48 1.85 2.18 2.89 12- 30.00 35.00 39.00 Phenolphthalein 10- 39.50 3.20 39.75 39.90 39.95 39.99 3.50 3.90 4.20 8- 4.90 pH = 7.00 at equivalence point 40.00 40.01 7.00 9.10 9.80 10.10 10.50 10.79 6- 40.05 Methyl red. 4- 40.10 40.25 40.50 2- 11.09 11.76 12.05 12.30 12.43 41.00 45.00 50.00 60.00 70.00 10 20 30 40 50 60 70 80 80.00 12.52 Volume of NaOH added (mL) OH- Na CI H20 Total volume (mL) 40 + 0 = 40 40 + 20 = 60 40 + 40 = 80 40 + 60 = 100

Instrumental acid-base titrations use a pH meter to monitor the changes in pH and volume. The equivalence point is found from the volume at which the curve has the steepest slope.(a) Use Figure to calculate the slope pH/V for all pairs of adjacent points and to calculate the average volume (V(avg)) for each interval.(b) Plot ΔpH/ΔV vs. V(avg) to find the steepest slope, and thus the volume at the equivalence point. (For example, the first pair of points gives ΔpH= 0.22, ΔV=10.00 mL; hence, ΔpH/ΔV=0.022 mL⁻¹, and V(avg)=5.00 mL.)