Acids burn.

Bases burn.

VI. Strength of Acids and BasesA. Strong acids and bases…

1. completely dissociate (come apart) or ionizes 100% of the molecules become ions2. are strong electrolytes and dangerous!

Ex. acids: HCl, HBr, HI, HNO3, H2SO4, HClO4

bases: NaOH and other Group 1 or 2 hydroxides

B. Weak acids and bases… 1. dissociate or ionize very little

maybe only 1% of molecules become ions2. are weak electrolytes

Ex: acids: acetic acid, carbonic, and many others bases: ammonia and many others

STRONG ACIDS

STRONG Bases

C. pH Scale1. In any solution, if you pay attention only to the

concentration of hydronium H3O+ (same as H+ !!!)

and hydroxide OH- ions…

…and use brackets [ ] to mean “the concentration of…”

then..

In an acidic solution: [H+] > [OH-]

In a neutral solution: [H+] = [OH-]

In a basic solution: [H+] < [OH-]

Ex. Is the solution shown at right

acidic, basic or neutral?

H+

OH-

H+

H+

OH-

H+

OH- H+

H+

OH-

OH-

OH-

OH-

2. The pH scale is used to express how acidic or basic a solution is.

a/ The pH scale goes from 0 to 14

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14

neu

tralstronger acids

more acidicmore [H+] or [H3O+]

stronger basesmore basicmore [OH-]

b/ pH = 7 means a neutral solution with [H+] = [OH-]

Lower pH (< 7): more acidic with [H+] > [OH-]

Higher pH (> 7): more basic with [OH-] > [H+]

Ex. As acid is added to base, what happens to the..

…the pH?

…the acidity? …the basicity?

…the H3O+ concentration? …the OH- concentration?

Ex. Which pH value is most basic?

11 13 2 7 4

Ex. Which pH value it most acidic?

11 13 2 7 4

Ex. Which pH value has the greatest [H3O+]?

11 13 2 7 4

Ex. Which pH value has the greatest [OH-]?

11 13 2 7 4

Sometimes it is written right to left:

Ex. The list at right

gives the pH’s of some

common solutions.

a/ Write A (acid), B (base) and N (neutral) next to each

b/ Put them in order…

…from strongest acid to strongest base:

…of increasing H+ (or H3O+) concentration.

…of increasing OH- concentration.

bleach: 13

blood: 7.4

coffee: 5

OJ: 3

pure water: 7

3/ pH is logarithmic. This means that…

a change …means a change in pH of: in concentration of:

1 101 or 10x

2 102 or 100x

3 103 or 1000x

etc

Ex. Which has a greater [H+] or [H3O+]:

urine (pH 6) or pure water (pH 7)?

How much greater?

Which has a greater [OH-]?

How much greater?

Ex. Which has a greater [H+]: soapy water (pH 12) orbaking soda (pH 9)?

How much greater?Which has a greater [OH-]?How much greater?

Ex. Which has a greater [OH-]: a can of soda (pH 3) or black coffee (pH 5)?

How much greater?

Which has a greater [H30+]?

How much greater?

Ex. The pH of a solution changes from 4 to 3. Did the [H+] decrease or increase? By what factor?Did the [OH-] dec. or incr.? By what factor?