Arrhenius

1
Chapter 14

• Arrhenius
• Acid create H in water
• Base create OH- in water
• Bronsted-Lowery
• Acid donates proton (H)
• Base accepts proton (H)
• Hydronium ion - H3O

2

• Conjugate pairs
• HCN/CN- HCl/Cl- NH3/NH4
• Acid dissociation constant
• Equilibrium expression for its dissociation
• Ka
• HF ?? H F-
• Ka HF- / HF
• Strong vs weak

3

• Oxyacids
• HNO3, HClO4, H2SO4
• Organic Acids
• COOH group HC2H3O2 (CH3COOH)
• Monoprotic, diprotic, triprotic
• HCl, H2SO4, H3PO4

4

• Water as an acid and base
• H2O H2O ?? H3O OH-
• Amphoteric
• Dissociation constant for water
• Kw H3OOH- 1.0 x 10-14
• OH- 1.0 x 10-5 H3O ?
• H3O 1.0 x 10-14 / 1.0 x 10-5 1.0 x 10-9

5

• pH
• pH - logH
• pOH
• pOH - logOH-
• pH pOH 14
• Calculate the pH and pOH of a 1.0 x10-9M HCl
  solution.
• pH - log(1.0x10-9) 9.0 pOH 14 9 5.0

6

• What is the H if the pH 4.4
• pH -logH H 10-pH
• H 10-4.4 3.98 x 10-5 4.0 x 10-5M
• pH of strong acids
• Completely dissociates so acid H
• pH of weak acids
• Have to do an equilibrium problem using Ka
• Follow the same process

7

• HF ?? H F-
• Ka HF- / HF 7.2 x 10-4
• Calculate the pH of a 1.0 M HF solution
• Chem. Initial Equil.
• H 0 x
• F- 0 x
• HF 1.0 1.0 x 1.0 (small x)
• Ka HF- / HF 7.2 x 10-4
• 7.2 x 10-4 x2 / 1.0 x 2.7 x 10-2 M
• pH -log(2.7 x 10-2) 1.57

8

• pH of a mixture of acids
• Focus on the strongest acid
• Our HF example also contained H2O but we can
  ignore it since its constant is 1.0 x 10-14
• and HF is much larger, 7.2 x 10-4
• Percent dissociation
• diss. H / HAo x 100

9

• What is the pH of an aqueous solution of 1.00M
  HCN and 5.00M HNO2.
• HCN Ka 6.2 x 10-10
• HNO2 Ka 4.0 x 10-4
• H2O Kw 1.0 x 10-14
• Strongest acid is HNO2 so we use it

10

• HNO2 Ka 4.0 x 10-4
• HNO2 ?? H NO2-
• Chem. init. equil
• HNO2 5.00 5.00-x 5.00 (x is small)
• H 0 x
• NO2- 0 x
• 4.0 x 10-4 x2 / 5.00
• x 4.5 x 10-2
• pH -log(4.5 x 10-2) 1.35

11

• Bases
• We calculate OH- just like H but use Kb
  instead of Ka
• pH of strong bases
• Completely dissociates so the Base OH-
• pH of weak bases
• Focus on the strongest base present and do an
  equilibrium problem

12

• Calculate the OH- for a 15.0 M NH3 solution, Kb
  1.8 x 10-5.
• NH3 H2O ?? NH4 OH-
• Kb NH4OH- / NH3 1.8 x 10-5
• Chem. Init. Equil
• NH4 0 x
• OH- 0 x
• NH3 15.0 15.0 x 15.0

13

• Chem. Init. Equil
• NH4 0 x
• OH- 0 x
• NH3 15.0 15.0 x 15.0
• Kb NH4OH- / NH3 1.8 x 10-5
• 1.8 x 10-5 x2 / 15.0
• x 1.6 x 10-2
• pOH -log(1.6 x 10-2) 1.80
• pH 14 1.80 12.20

14

• Strong bases make weak adics
• Strong acids make weak bases
• So the larger the Ka the smaller the Kb
• Ka x Kb Kw

15

• Polyprotic acids
• Dissociate one proton at a time
• Follow the same steps as an equil. problem
• Calculate the pH as well as the concentration of
  all other chemicals present in a 5.0M H3PO4
  aqueous solution.
• H3PO4 Ka1 7.5 x 10-3
• H2PO4- Ka2 6.2 x 10-8
• HPO42- Ka3 4.8 x 10-13

16

• H3PO4 ?? H H2PO4-
• Ka1 7.5 x 10-3 HH2PO4- / H3PO4
• Chem. init equil
• H 0 x
• H2PO4- 0 x
• H3PO4 5.0 5.0 x 5.0
• 7.5 x 10-3 x2 / 5.0
• x 0.19 H H2PO4-

17

• H2PO4- ?? H HPO42-
• Ka2 6.2 x10-8 HHPO42-/H2PO4-
• Chem init equil
• H 0.19 0.19x 0.19
• HPO42- 0 x
• H2PO4- 0.19 0.19 x 0.19
• 6.2 x10-8 (0.19)x / 0.19 x 6.2 x10-8
• HPO42- 6.2 x 10-8

18

• HPO42- ?? H PO43-
• Ka3 4.8 x 10-13 HPO43-/HPO42-
• Chem init. equil.
• H 0.19 0.19 x 0.19
• PO43- 0 x
• HPO42- 6.2 x 10-8 6.2 x10-8 -x 6.2x10-8
• 4.8 x 10-13 (0.19)x / 6.2 x 10-8
• x 1.6x10-19
• PO43- 1.6 x 10-19

19

• OH-
• Kw 1.0 x 10-14 HOH-
• 1.0 x 10-14 (0.19)OH-
• OH- 5.3 x 10-14

20

• Sulfuric acid
• Similar to phosphoric acid except the first
  dissociation is complete and we can use that info
  for the second dissociation problem.
• Calculate the SO42- in a 1.0M aqueous H2SO4
  solution.
• H2SO4 ? H HSO4-
• H2SO4 H HSO4- 1.0

21

• HSO4- ?? H SO42-
• Ka2 1.2 x 10-2 HSO42- / HSO4-
• Chem. init. equil.
• H 1.0 1.0 x 1.0
• SO42- 0 x
• HSO4- 1.0 1.0 x 1.0
• 1.2 x 10-2 (1.0)x / 1.0 x 1.2 x 10-2
• SO42- 1.2 x 10-2 M

22

• Acid/Base properties of salts
• Salts from strong acids/bases produce neutral
  solution, NaCl, KNO3 etc
• Salts from weak acid, strong base produce basic
  solutions, NaF, KC2H3O2
• F- H20 ?? HF OH-
• Salts from strong acid, weak base produce acidic
  solutions, NH4Cl
• NH4 H2O ?? NH3 H3O

23

• Highly charged metal ions like Al3 produce
  acidic solutions when hydrated, because of the
  large charge it is easier to release H
• Ka x Kb Kw
• So if you know a chemicals Ka or Kb you can
  determine the corresponding Ka / Kb as needed

24

• Calculate the pH for a 0.1 M NH4Cl aqueous
  solution. Kb 1.8 x 10-5 for NH3
• NH4 reacts with water like an acid so we need
  its Ka. We get it from the Kb
• Ka Kw / Kb 1.0 x 10-14 / 1.8 x 10-5 5.6 x
  10-10
• NH4 H2O ?? NH3 H3O
• Chem init. equil.
• NH4 0.1 0.1 x 0.1
• NH3 0 x
• H3O 0 x

25

• Ka 5.6 x 10-10 NH3H3O / NH4
• 5.6 x 10-10 x2 / 0.1
• x 7.5 x 10-6 H3O
• pH -log (7.5 x 10-6) 5.13

26

• Structure effect HClO vs HClO4
• The extra oxygens draw the electrons away from
  the hydrogen allowing it to be released more
  easily. Thus HClO4 is stronger
• How do HNO2 and HNO3 compare?

27

• Acid/Base properties of oxides
• Non-metal oxides produce acids when mixed with
  water
• SO3 H2O ? H2SO4
• CO2 H2O ? H2CO3
• Metal oxides produce bases when mixed with water
• CaO H2O ? Ca(OH)2
• Na2O H2O ? NaOH

28

• Lewis Acid/Bases
• Acids accept electron pairs
• Bases donate electron pairs
• BH3 NH3 ? BH3NH3
• BH3 is the acid
• NH3 is the base