I performed an experiment to find the pH of strong acid, weak acid, salt, and bu
ID: 839168 • Letter: I
Question
I performed an experiment to find the pH of strong acid, weak acid, salt, and buffer solutions. I used HCl, HC2H3O2 solutions, and buffer solutions of HC2H3O2/NaC2H3O2. I also added HCl and NaOH solutions to separate samples of buffer solutions.
1.) Concentration of HCl / Measured pH / Theoretical pH
Find the theoretical pH
1.0x10^-1 .... 0.98 ..... ????
1.0x10^-2 .....2.45 ...... ?????
1.0x10^-3 .... 3.25......????
1.0x10^-4 ..... 5.51 ..... ????
2.) Preparing HC2H3O2 Solutions and determining pH
Find the theoretical pH from the concentration of HC2H3O2 and the measured pH
1.0x10^-1 .....2.76....????
1.0x10^-2 ..... 3.10....????
1.0x10^-3 ...... 3.59 .... ????
1.0x10^-4 ...... 4.07.....????
3.)Given the concentrations of HC2H3O2, find the *calculated Ka* of HC2H3O2 and the *literature Ka* based on the pH data
Concentration:
1.0x10^-1
1.0x10^-2
1.0x10^-3
1.0x10^-4
Explanation / Answer
1.) Concentration of HCl / Measured pH / Theoretical pH
HCl -----> H+ + Cl-
As HCl is a strong acid, it will ionise 100%. Thus, [H+] produced will be equal to that of HCl.
Theoretical pH = - log [H+] = - log [HCl]
1.0x10^-1 .... 0.98 ..... theoretical pH= -log (0.1)= 1
1.0x10^-2 .....2.45 ...... theoretical pH= -log (0.01)= 2
1.0x10^-3 .... 3.25...... theoretical pH= -log (0.001)= 3
1.0x10^-4 ..... 5.51 ..... theoretical pH= -log (0.0001)= 4
2.) Preparing HC2H3O2 Solutions and determining pH
As HC2H3O2 is a weak acid, it will not ionise 100%. Thus, first we have find the degree of ionisati of the acid as follows:
HC2H3O2 -----> H+ + CH3COO-
(c-x) x x
Ka= 1.8 x 10