Acid and Base Strength

1
Acid and Base Strength
2
Acids

• Have a sour taste.

3
Acids

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

4
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

5
Acids

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

6
Bases

• Have a bitter taste.

Coffee itself is acidic, but it contains an
alkaline compound caffeine which contributes
to its bitter taste.
7
Bases

• Feel slimy or slippery to the touch.

8
Bases

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

Litmus pH scale.
9
Bases

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

10
Bases

• Are electrolytes.

11
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.

12
Review

• pH Scale
• Traditionally 0 - 14.
• Can have pH lt 0 or gt 14.
• pH lt 7 ? Acidic solution.
• pH 7 ? Neutral solution.
• pH gt 7 ? Basic solution.

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pH Scale
pH Scale
Acidic Basic
14
HCl, A Strong Acid
15
HF, A Weak Acid
16
As H Increases, OH-1 Decreases
OH-1
H
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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.

18
H and OH-1 in Water

• If H 1x10-3 M, what is OH-1?
• HOH-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?
• HOH-1 1x10-14
• H(1x10-8 M) 1x10-14
• H (1x10-14) / (1x10-8 M)
• H 1x10-6 M

19
pH

• pH power of Hydrogen
• negative logarithmic (powers of ten) scale.
• pH -log10H
• 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

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A Few Words About Logarithms

• 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

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H3O1 and OH-1
H3O1
OH-1
22
Calculations Involving pH, pOH, H, and OH-
of strong Acids and Bases
pH -log H pOH -log OH- pOH pH
14  
23
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