Acids and Bases

1
Chapter 15

• Acids and Bases

2
Introduction

• Proton transfer reactions
• Acids
• H H2O ? H3O
• H20 HCl ? H30 Cl-
• Bases
• NaOH ? Na OH-
• NH3 H2O ? NH4 OH-

3
Acid-Base Strength

• Strength of acids and bases is due to degree of
  ionization.
• Strong acids and bases are completely dissociated
• Weak acids and bases are not dissociated
  completely.

4
Strong Acids

• HCl Hydrochloric acid
• HBr Hydrobromic acid
• HI Hydroiodic acid
• HNO3 Nitric acid
• H2SO4 Sulfuric acid
• HClO4 Perchloric acid

5
Strong Bases

• LiOH Lithium hydroxide
• NaOH Sodium hydroxide
• KOH Potassium hydroxide
• Ba(OH)2 Barium hydroxide
• Ca(OH)2 Calcium hydroxide
• Mg(OH)2 Magnesium hydroxide

6

• Strong acids and bases dissociate in water.
• A concentrated weak acid will never be strong.

7
Bronsted-Lowry Acids and Bases

• Acids are proton (H) donors.
• Must have an H attached, but not all Hs are
  ionizable.
• CH3COOH only the last H is acidic
• Bases are proton (H) acceptors.
• OH- is a strong base H OH- ? H2O
• NH3 is an important weak base
• NH3 H ? NH4

8
Number of Protons

• Monoprotic acids HCl, HNO3, HBr, HI
• Diprotic acids H2SO4, H2CO3
• Triprotic acids H3PO4

9
Amphiprotic

• When an substance can act as either an acid or a
  base it is called amphiprotic
• HCO3- ? CO32- H
• proton donated, acid
• HCO3- H ? H2CO3
• proton accepted, base

10
Water Is Amphiprotic

• H2O ? H OH-
• H2O H ? H3O

11
Conjugate Acid-Base Pairs

• When an acid donates a proton, the conjugate base
  is left.
• HCO3- ? CO32- H
• CO32- is the conjugate base of HCO3-

12

• When an base accepts a proton, the conjugate acid
  is formed.
• SO42- H ? HSO4-
• HSO4- is the conjugate acid of SO42-

13

• The stronger the acid, the weaker its conjugate
  base.
• The stronger the base, the weaker its conjugate
  acid.

14
Properties of Acids and Bases

• Neutralization When an acid reacts with a base
  a salt and water are formed.
• Metals When an acids reacts with an active
  metal, a salt and hydrogen gas are formed.
• Carbonates and Bicarbonates When an acid reacts
  with CO32- or HCO3-, carbon dioxide and water are
  formed.

15

• For pure water
• H3O OH- 1.0 x 10-7

16
Examples

• If the H3O of a solution is 1 x 10-6, the
  OH- is
• 1 x 10-14 / 1 x 10-6 1 x 10-8

17

• What is the OH- of a 0.001 M HCl solution?
• 1 x 10-14 / 1 x 10-3 1 x 10-11 M

18
pH of solutions
0

• pH - logH3O
• H3O 10-pH

19
Laws of Exponents

• am x an amn
• am / an am-n

20
Examples
0

• H3O 10-8 M
• pH 8
• H3O 10-10 M
• pH 10
• H3O 10-2 M
• pH 2

21
pOH of solutions
0

• pOH - logOH-
• OH- 10-pOH

22
Examples
0

• OH- 10-8 M
• pOH 8
• OH- 10-10 M
• pOH 10
• OH- 10-2 M
• pOH 2

23
0

• pH pOH 14.00
• pH 8, then pOH 6
• pH 2, then pOH 12

24
Calculate H3O, OH-, pH, pOH
0
25
Titration
0

• Titration is a laboratory procedure used to
  measure the number of moles of acid in an unknown
  acid solution by using a known, standardized base
  solution.

26
0
27
0

• The equivalence point is the point where the
  number of moles of acid equal the number of moles
  of base.
• An indicator is used to tell when the equivalence
  point is reached. The indicator changes color
  when a certain pH is attained.
• The endpoint is the point where the indicator
  changes color.

28
Equivalents
0

• 1 Equivalent MW/charges
• 1 Eq Na 23.0 g
• 1 Eq Ca2 20.0 g
• 1 Eq Al3 9.0 g
• 1 Eq Cl- 35.5 g
• 1 Eq O2- 8.0 g
• 1 Eq 1000 mEq

29
Normality
0

• Normality Eq/Liter
• Acid concentration can be reported as molarity or
  normality.
• 1 M HCl 1 N HCl
• 1 M H2SO4 2 N H2SO4

30
Question
0

• Kaochlor, a 10 KCl solution, is an oral
  electrolyte supplement administered for potassium
  deficiency. How many milliequivalents of K are
  in a 30 mL dose?

31
Calculations
0

• 10.00 mL of HCl is placed in a flask. If 25.68
  mL of 0.9863 M NaOH is needed to reach the
  endpoint, what is the molarity of the acid? What
  is the normality?

32
0

• 20.00 mL of H2SO4 is placed in a flask. It
  takes 41.89 mL of 0.9863 M NaOH to reach the
  endpoint. What is the normality of the acid?
  What is the molarity of the acid?