More Solutions, A-B Rxns, and LeChatelier

1
More Solutions, A-B Rxns, and LeChateliers
Principle
2
Water and Water Solutions
3
Water and Water Solutions
4
How Can Molecular Compounds Produce Ions In Water?

• If solution conducts, the charge carriers (ions)
  must have resulted from rxn of the molecule with
  water.
• e.g., HC2H3O2 H2O C2H3O2- H3O

5
Investigate This 2.67
What are the properties of aqueous solutions of
gases?
6
Results of 2.67a Conductivity Tests
distilled water (N2, O2, CO2 (aq))
CO2 (aq)
NH3 (aq)
HCl (aq)
C6H12O6 (aq)
Meter lights if solution conducts.
7
Results of 2.67b pH Tests
pH1 2 3
4 5 6
indicator added to solutions of known pH
12 11 10
9 8 7
distilled water (N2, O2, CO2 (aq))
CO2 (aq)
NH3 (aq)
HCl (aq)
C6H12O6 (aq) plus same indicator
8
Summary for Investigate This 2.67

• Which cmpds (without water) are ionic? How can
  you tell?
• Which mixtures of cmpds water contain ions?
• Are there significant amounts of OH- present?
  H3O?
• Write eqns for any rxns that occur between gas
  water.

9
Acid-Base Reactions
10
The Arrhenius View

• Acid - yields H when added to water
• HCl(g) H2O(l) H(aq) Cl- (aq)

unbalanced
11
Arrhenius View of Neutralization
12
The Brønsted View

• More general approach, not limited to water
• acid proton (H) donor
• base proton (H) acceptor
• Neutralization proton (H) transfer

13
Why is HCl a Brønsted Acid?
14
Why is Ammonia a Brønsted Base?
acid
base
The double arrow is used to show that this is an
equilibrium (reaction is incomplete).
15
Water Autoionizes in a Brønsted Rxn
H-O-H H-O-H ? H3O OH-
acid
base
Position of this equilibrium lies very far to the
left and explains waters 0 conductivity. Pure
water contains very few ions.
16
pH -log10H(aq) -log10H3O
Acidic Neutral

Basic
17
Le Chateliers Principle
A system at equilibrium responds to a disturbance
(stress) in a way that minimizes the effect of
the disturbance (stress).
18
Equilibrium and LeChateliers Principle
(Investigate This 2.85)
NH3 H2O ? NH4 OH-

• When water and NH4Cl are mixed, this equilibrium
  is established. (Cl- is a spectator.)
• Add 2-3 drops of water to NH4Cl vial, cap, and
  mix.
• Note odor.
• Odor of NH3 means equilibrium lies to the left
• No smell equilibrium lies to the right
• Add OH- (disturb the equilibrium).
• Add 2-3 drops of water to NH4Cl-NaOH vial and
  mix.
• How does the position of equilibrium compare to
  NH4Cl alone?

19
More Net Ionic Equations
20
Problem Write the net ionic equation for the
reaction of sodium hydroxide and acetic acid in
water.
whole formula
ionic eqn
net ionic eqn
21
Problem Write the net ionic equation for the
reaction of sodium hydroxide and acetic acid in
water.