Acid and Base Equilibrium

1
Acid and Base Equilibrium

• CHM1020
• Chapter 10

2
AB CD ? AD CB
Ag
NO3-
Na
Cl-
Ag
NO3-
Na
Cl-
AgNO3 (aq) NaCl (aq) ?
AgCl(s) NaNO3 (aq)
Double replacement reactions are driven by the
formation of a solid, gas or water as one of the
products.
3
Acid Base Reactions are Double Replacement where
H2O is formed
H
Cl-
Na
OH-
H
Cl-
Na
OH-
HCl (aq) NaOH (aq) ?
H2O(l) NaCl (aq)
HCl is the acid. NaOH is the base.
4
Arrhenius

• In water, H becomes H3O
• Acid A substance that make H (H3O) when
  dissolved in water.
• Base A substance that makes OH- when dissolved
  in water.
• An acid/base reaction occurs when and H from an
  acid reacts with an OH- from a base.

5
Carbonates can also neutralize acids
H
Cl-
Na
CO32-
H
Cl-
Na
CO32-
2HCl (aq) Na2CO3 (aq) ?
H2CO3 2NaCl (aq)
H2O(l) CO2(g)
Carbonic acid decomposes H2CO3 ? H2O(l) CO2(g)
6
Brønsted-Lowry Definition

• Acid A proton donor.
• Base A proton acceptor.
• An acid base reaction is one where there is a
  proton transfer.
• A broader definition than the Arrhenius
  definition.
• conjugate base The acid without an H.
• conjugate acid The base with an H.

7
Acid Base Pairs
8
A standard acid/base reaction
Acid Base ? c. base c. acid
CH3COOH H2O ? CH3COO- H3O
ex
NH3 H2O? NH4 OH-
9
More on Acid Base reactions

• Water is amphoteric or amphiprotic, it can act as
  both an acid and a base.
• All acid base reactions are equilibrium reactions
• The equilibrium lies to the side of the weaker
  acid.
• When the equilibrium lies to the right, a lot of
  reaction occurs and there is often heat released
  or there is a color change.
• When the equilibrium lies to the left very little
  reaction occurs. (no heat)

10
Acids

• Strong acids Dissociate completely when
  dissolved in water.
• HCl, HNO3
• HCl H2O ? Cl- H3O (99 to the right)
• Weak acids only dissociate a little bit.
• CH3CO2H
• CH3COOH H2O ? CH3COO- H3O
• (less than 1 to the right)

11
1.00 M Acetic acid, a weak acid

• CH3COOH (aq) H2O(l) ? H3O(aq) CH3COO-(aq)
• The Ka for this reaction is 1.8 x 10-5. Since
  little of the CH3CO2H dissociates, we can call it
  1 M.
• For every H3O there will be one CH3COO-. Let
  these concentrations x
• xH CH3COO- .00042

12
Base

• Strong base dissociates completely when
  dissolved in water.
• NaOH, KOH
• NaOH ? Na(aq) OH-(aq)
• Weak base Makes only a little bit of OH-
• NH3
• NH3 H2O ? NH4 OH-

13
Water

• Water auto-ionizes
• H2O H2O ? H3O OH-
• acid base
  10-7M 10-7M

14
Acids and pH
15
The big six

• H OH- 10-14
• pH -log H
• pOH -log OH-
• H10-pH
• OH-10-pOH
• pH pOH 14

16
pH questions