1. Strengths of Acids and Bases
SCH 11U

2. Ionization
Acid molecules ionize in water; the neutral molecule breaks apart into charged ions
HCl  H Cl –
H2SO4  2H+ + SO42-

3. Degree of Ionization
Some acids tend to ionize to a greater degree than others
Strong acids completely ionize in water into their ions
100% H Cl H+ +
Cl-

4. Degree of Ionization
Weak acids only partially ionize in water to form only a few ions. The majority of the molecules remain as neutral ions. 1%
C2H3O2
C2H3O2 H H+ +

5. Dissociation Bases dissociate in water into their ions
Strong bases dissociate completely
NaOH  Na+ + OH-
Weak bases only partially dissociate
Ca(OH)2  Ca OH-

6. Concentration
The concentration of an acid or base refers to the amount of acid or base molecules in the total solution.
c (mol/L) = n (mol)
v (L)
Dilute acids have a relatively small amount of solute per volume of solution
Concentrated acids have a relatively high amount of solute per volume of solution

7. Concentration
Concentrated
Dilute

8. Concentration
Concentrated
Dilute

9. Strength
Strength of an acid or base depends on the hydrogen or hydroxide ion concentration.
The higher the hydrogen ion, concentration the stronger the acid
> [H+] stronger acid
The higher the hydroxide ion, concentration the stronger the base
> [OH-] stronger base

10. Ion Concentration
Strong acids and bases ionize or dissociate completely
If you know the concentration of the acid we can predict the concentration of the ions using the mole ratio
HCl  H Cl –
0.25 mol/L ?

11. Ion Concentration
HCl  H Cl –
0.25 mol/L ?

12. Ion Concentration
H2SO4  2H+ + SO42-
0.125 mol/L ?

13. Ion Concentration
NaOH  Na+ + OH-
0.36 mol

14. Measuring Strength pH stands for power of hydrogen
pH scale is a measure of acidity of a substance
It is a simple way to express the hydrogen ion concentration

15. pH Scale Scale ranging from 0-14 0-7 acidic, 7-14 basic, 7 neutral
Each number is a ten-fold (10X) jump in concentation
ie) pH 3 is 10 times more acidic than pH 4

16. pH Calculations
Use the following equation to find a pH if given a concentration:
pH = - log [H+]

17. pH Calculations [H+] = 1.0 x 108 pH = [H+] = 2.5 x 105 pH =

18. [H+] Calculations
Use the following relationship to determine the hydrogen ion concentration if given pH
[H+] = 10-pH
[H+] = antilog (- pH)

19. [H+] Calculations
pH = 5 [H+] =
pH = [H+] =
pH = [H+] =

20. Try These…