Acid and Base Strength

Acid and Base Strength

Acids

• Have a sour taste.

Acids

• Turn blue litmus red.
• Turn methyl orange red.

Acids

• Will react with:
• some metals to produce a salt and H2.
• metal oxides to produce a salt and H2O.
• metal carbonates to produce a salt, H2O, and CO2.
• bases to produce a salt and H2O.
• Mg + 2HCl  MgCl2 + H2
• MgO + 2HCl  MgCl2 + H2O
• MgCO3 + 2HCl  MgCl2 + H2O + CO2
• Mg(OH)2 + 2HCl  MgCl2 + 2H2O

Acids

• Are electrolytes.
• Conduct an electric current when dissolved.

Bases

• Have a bitter taste.

Coffee itself is acidic, but it contains an alkaline compound – caffeine – which contributes to its bitter taste.

Bases

• Feel slimy or slippery to the touch.

Bases

• Turn red litmus blue.
• Turn methyl orange yellow.
• Turn phenolphthalein pink.

Litmus pH scale.

Bases

• React with acids to produce salt and H2O.
• HCl + NaOH  NaCl + H2O

Bases

• Are electrolytes.

Review

• Properties of Acids
• Taste sour.
• Turn litmus red.
• Proton (H+) donors.
• Inc. [H3O+] in aqueous solutions.

• Properties of Bases
• Taste bitter.
• Turn litmus blue.
• Proton acceptors.
• Inc. [OH-] in aqueous solutions.

Review

• pH Scale
• Traditionally 0 - 14.
• Can have pH < 0 or > 14.
• pH < 7  Acidic solution.
• pH = 7  Neutral solution.
• pH > 7  Basic solution.

pH Scale

Acidic Basic
0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
pH Scale

HCl, A Strong Acid

HF, A Weak Acid

As [H+] Increases, [OH-1] Decreases

1x10-13 M
1x10-12 M
1x10-11 M
1x10-10 M
1x10-9 M
1x10-8 M
1x10-7 M
1x10-6 M
1x10-5 M
1x10-4 M
1x10-3 M
1x10-2 M
1x10-1 M
1x10-13 M
1x10-12 M
1x10-11 M
1x10-10 M
1x10-9 M
1x10-8 M
1x10-7 M
1x10-6 M
1x10-5 M
1x10-4 M
1x10-3 M
1x10-2 M
1x10-1 M
[H+]
[OH-1]
Neutral Solution
Acid added to neutral solution
Base added to neutral solution

[H+] and [OH-1] in Water

• In any aqueous solution:
• [H+] [OH-1] = 1x10-14
• As [H+] goes up, [OH-1] must decrease.
• As [OH-1] goes up, [H+] must decrease.
• In other words, adding an acid to water causes the solution to become more acidic and less basic.
• Adding a base to water causes the solution to become less acidic and more basic.

[H+] and [OH-1] in Water

• If [H+] = 1x10-3 M, what is [OH-1]?
• [H+][OH-1] = 1x10-14
• (1x10-3 M)[OH-1] = 1x10-14
• [OH-1] = (1x10-14) / (1x10-3)
• [OH-1] = 1x10-11 M
• If [OH-1] = 1x10-8 M, what is [H+]?
• [H+][OH-1] = 1x10-14
• [H+](1x10-8 M) = 1x10-14
• [H+] = (1x10-14) / (1x10-8 M)
• [H+] = 1x10-6 M

pH

• pH = power of Hydrogen
• negative logarithmic (powers of ten) scale.
• pH = -log10[H+]
• If [H+] = 1x10-1 M,
• pH = -log(1x10-1 M) = 1
• If [H+] = 1x10-2 M,
• pH = -log(1x10-2 M) = 2
• If [H+] = 1x10-3 M,
• pH = -log(1x10-3 M) = 3

Calculations Involving pH, pOH, [H+], and [OH-] of strong Acids and Bases

pH = -log [H+]
pOH = -log [OH-]
pOH + pH = 14
 

[H3O+1] and [OH-1]

[H3O+1]
[OH-1]

pH and pOH

• What are the pH values of the following solutions?
• 1x10-1 M H+
• pH = -log(1x10-1 M) = 1
• 1x10-3 M H+
• pH = -log(1x10-3 M) = 3
• 1x10-5 M H+
• pH = -log(1x10-5 M) = 5
• 1x10-1 M OH-1
• [H+] = (1x10-14) / (1x10-1 M) = 1x10-13 M
• pH = -log(1x10-13 M) = 13