4/9 Notes – pH

E. Acid Base Strength

1. Strong Acid/Base

a. Def – completely ionizes in solution (completely breaks apart); corrosive

b. Example

Sulfuric acid, H₂SO₄

Sodium hydroxide, NaOH

2. Weak Acid/Base

a. Def – does not completely ionize in solution (breaks apart very little); not as dangerous

b. Example

Acetic acid, HCH₃COO (Vinegar)

2. pH Scale

A. Def – logarithmic scale showing the strength of acids and bases

B. Identifying acids and bases

Acids range from 1 to 7

7 is neutral

7 – 17 is a base

C. Finding pH and pOH

1. pH

a. Def = - log [H₃O⁺]

= - log of the hydronium ion concentration (which is signified by M)

b. Example

What is the pH of a substance that has the hydronium ion concentration of 1 x 10^-3?

pH = - log [H₃O⁺]

- log [1 x 10^-3]

pH = 3

D. pOH

1. Def = - log [OH^-]

= - log of the hydroxide ion concentration (same as pH, but for hydroxide ion instead of hydronium ion)

2. Example

What is the pOH of a hydroxide ion concentration of 5.68 x 10^-4 M?

pOH = - log [OH^-]

- log [5.68 x 10^-4]

pOH = 3.25

E. Putting it all together

1. pH + pOH = 14

2. Example

What is the pOH, if the pH is 1.34?

pH + pOH = 14

1.34 + pOH = 14

pOH = 12.66