Calculate the expected pH of the buffer after the addition of 1.0 mL of 1M HCl. Remember that you are using 50 mL of the buffer, so be sure to calculate the moles of acetic acid and acetate in 50 mL of the buffer.

Explanation:

From the given information;

the molecular molarity of the acid and  base are as follows:

For acid : 5 mL × 0.20 M = 0.1 mmol

For base: 5 mL × 0.20 M = 0.1 mmol

However;

0.05 m  × 1.0 M = 0.05 mmol of acid HCl

Similarly, When the acid undergoes reaction with the base; the amount of acid and base left are as follows:

Amount of acid left:

0.1 + 0.05 = 0.15 mmol

Amount of base left:

0.1 - 0.05 = 0.05 mmol

The formula for calculating the Buffer pH is:

Recall that for Acetic, the acid dissociation constant = 4.74

Then:

pH = 4.74 -  0.4775

pH = 4.26

Therefore, the decrease in pH is about 0.48 units