Strong Acids and Bases
What is the pH of 10-3 M HCl solution?
What is the pH of 10-5 M HCl solution?
What is the pH of 10-7 M HCl solution?
What is the pH of 10-8 M HCl solution?
-2
-3
log concentration
-4
-5
-6
-7
-8
-9
0
1
2
3
4
5
6
7
8
pH
9
10
11
12
13
14
0.001 M HCl
-2,0
[Cl-]
-3,0
-4,0
[OH-]
[H+]
log concentration
-5,0
-6,0
-7,0
-8,0
-9,0
0
1
2
3
4
Equilibrium pH= 3.0
5
6
7
8
pH
9
10
11
12
13
14
10-5 M HCl
-2,0
-3,0
-4,0
[OH-]
[H+]
[Cl-]
log concentration
-5,0
-6,0
-7,0
-8,0
-9,0
0
1
2
3
4
5
6
Equilibrium pH= 5.0
7
8
pH
9
10
11
12
13
14
10-7 M HCl
-2,0
-3,0
-4,0
[OH-]
[H+]
log concentration
-5,0
-6,0
[Cl-]
-7,0
-8,0
-9,0
0
1
2
3
4
5
6
7
8
Equilibrium pH= 6.8
pH
9
10
11
12
13
14
10-8 M HCl
-2,0
-3,0
-4,0
[OH-]
[H+]
log concentration
-5,0
-6,0
-7,0
[Cl-]
-8,0
-9,0
0
1
2
3
4
5
6
7
8
Equilibrium pH= 7.0
pH
9
10
11
12
13
14
HCl ------ > H+ + Cl –
H2O < ====== > H+ + OHpH = - log [H+]
[H+] = [H+]HCl + [H+]H2O
In using the above assumption ([H+]H2O is negligible
wrt. [H+] coming from the strong acid) make sure
that the strong acid concentration is above 10-7 M.
Otherwise, the assumption does not hold.
pH of 10-3 M HCl solution= 3.0
pH of 10-5 M HCl solution= 5.0
pH of 10-7 M HCl solution= 6.8
pH of 10-8 M HCl solution= 7.0