From the pH, calculate the concentration of hydrogen ions. Next, find the concen

Question

From the pH, calculate the concentration of hydrogen ions. Next, find the concentration of the acetate ion. How would the concentration of hydrogen ion be related to the acetate ion? (Hint: look

at the formula for acetic acid.) Considering that acetic acid is the source of hydrogen and acetate ions in this sample, determine the actual concentration of acetic acid that is in the solution at the time when you measured the pH . Show a set of sample calculations.

You might develop a table like this one:

p H [H+] [C2H3O3-] [HC2H3O2]

0.10 M acetic acid 3.51

0.010 M acetic acid 4.30

0.0010 M acetic acid 5.75

0.0001 M acetic acid 6.28

Explanation / Answer

CH3COOH ------------------------------>CH3COO- + H+

0.10                                                       0                0 -----------------------> initial

0.10-x                                                   x                 x --------------------------> equilibrium

so x = [CH3COO-] = [ H+]

1) pH = 3.51

[H+] = 10^-pH = 10^-3.51 = 3.09 x 10^-4 M = x

[CH3COO- ] = [H+] = 3.09 x 10^-4 M

2) pH = 4.30

[CH3COO- ] = [H+] = 5.01 x 10^-5 M

3) pH = 5.75

[CH3COO- ] = [H+] = 1.78 x 10^-6 M

4) pH = 6.28

[CH3COO- ] = [H+] = 5.25 x 10^-7 M

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