Acid and Base StrengthAcid and Base Strength

AcidsHave a sour taste.

AcidsTurn blue litmus red.Turn methyl orange red.

AcidsWill 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

AcidsAre electrolytes.

Conduct an electric current when dissolved.

BasesHave a bitter taste.

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

BasesFeel slimy or slippery to the touch.

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

Litmus pH scale.

BasesReact with acids to produce salt and H2O.

HCl + NaOH NaCl + H2O

BasesAre electrolytes.

ReviewReview

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.

ReviewReview

pH Scale◦Traditionally 0 - 14.

Can have pH < 0 or > 14.◦pH < 7 Acidic solution.◦pH = 7 Neutral solution.◦pH > 7 Basic solution.

pH ScalepH Scale

Acidic Basic

0 1 2 3 4 5 6 7 8 9 10

11

12

13

14

pH Scale

HCl, A Strong AcidHCl, A Strong Acid

HF, A Weak AcidHF, 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 solutionBase added to neutral solution

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.

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 = 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

The logarithm of a number is the power to which you would have to raise a base to equal that number.◦ Unless otherwise indicated, assume the base is 10.

log(100) = 2◦ because 102 = 100

log(1000) = 3◦ because 103 = 1000

log(0.001) = -3◦ because 10-3 = 0.001

log(0.000 001) = -6◦ because 10-6 = 0.000 001

Concentrations of Hydronium and Hydroxide Ions

1.00E-14

1.00E-12

1.00E-10

1.00E-08

1.00E-06

1.00E-04

1.00E-02

1.00E+00

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

pH

Mo

lar [H3O+1]

[OH-1]

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

pH = -log [H+]

pOH = -log [OH-]

pOH + pH = 14

 

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