Chemistry 102: Acids: Rank acidity Highest to Lowest

Question

Rank the following solutions in order of increasing acidity, placing the most acidic solution at the left. (CH₃COOH is approximately 1.0% ionized at this concentration.)

pH=7.45

pH=0.00

[HCL]=0.15 M

[CH_3COOH]=0.15 M

Answer 1

We are given two pH values of 7.45 and 0.00. Of these, of course 0.00 is most acidic.

From the [HCl] and [CH3COOH] we can calculate the pH of these solutions as follows:

HCl is strong so [HCl] = [H+]

pH = -log [H+]

pH = -log 0.15

pH = 0.82

CH3COOH is weak with only 1% ionized

CH3COOH ==> CH3COO- + H+

[H+] = 1% x 0.15 M = 0.0015 M H+

pH = -log [H+]

pH = -log 0.0015

pH = 2.82

Arranging these from most to least acidic, we have

0.00 > 0.82(HCl) > 2.82(CH3COOH) > 7.45