2. Acid/Base Titration The Basics
a) The Technique
i) The Purpose to find out concentration of an unknown acid or base.
ii) Titration means to slowly and accurately add known [acid] to an unknown
[base] (or vice versa) using a buret, until base is exactly
1. Acid and Base Titration Calculations
a) Strong Acid and Strong Base
i) Example: We have 150 mL of NaOH at an unknown concentration. 75 mL
of 0.300 M HCl must be added to reach the equivalence point. What is
HCl + NaOH H2O + NaCl
Moles HCl = M x
prevents a significant change in pH when acid or base is added
0.1 mol HCl added to water
pH changes 6 units! (7 to 1)
0.1 mol HCl added to water
containing buffer system
pH changes only 0.08 units!
b) Acidic Bu
6. Electrochemical Cell - Quantitative
Voltage along the wire in an electrochemical cell depends on the half reactions.
a) Cell Potential
i) cell potential (E cell) is the maximum voltage of an electrochemical cell
ii) standard cell potential (Ecell) is t
5. Electrochemical Cell Applications
a) Factors Affecting Electrochemical Cells
a change means not 1 M (so the is removed from the E cell)
apply Le Chateliers principle:
eg/ Ag+ + e-
E cell = +0.80 V if [Ag+] = 1 M
a + E cell mea
Electrochemical cell spontaneous redox reaction produces electricity
Electrolysis add electricity to non-spontaneous reactions to make them go!
a) Electrolysis of Water
Water will NOT spontaneously reduce to H2:
2H2O + 2e- H2 + 2OH-
9. Oxidation vs. Reduction
a) Two Reactions in One!
i) Al (s) + Fe2O3 (s) Fe (l) + Al2O3 (s)
ii) There are two half reactions occurring!
Al (s) Al+3
(Al (s) loses 3 electrons)
Fe+3 Fe (l)
(Fe+3 gains 3 electrons)
iii) We must balance the half reactions
11. pH and pOH Calculations with Weak Acids and Bases
a) Weak Acids
i) Example: What is the pH of 0.400 M H2S?
Not 100% dissociated so [H2S] [H3O+]; so cant just pH = -log[0.400]
The weak acid will form an equilibrium:
H2S + H2O (l)
Salts dissociate 100% in water
The ions from the salt will either:
Be Spectator Ions
a) What is Hydrolysis?
i) Reaction between an ion from the salt with water.
ii) The ion will react with water to form a basic solution if
12. Electrochemical Cell Qualitative
Electrons are exchanged between two connected half-reactions.
Movement of electrons is electricity.
How can we harness the electricity from the following redox reaction?
13. Redox Titrations
Find an unknown concentration by slowly adding a known concentration until the
a) Find Concentration of a Reducing Agent
i) Procedure: 1. Titrate the reducing agent with KMnO4 (powerful oxidizing agent)
2. The reduc
10. Balancing Redox Reactions Using Oxidation
a) What are Oxidation Numbers?
Sample: K2Cr2O7 K is +1 Cr is +6
O is -2
They are not actual charges!
They are a bookkeeping system used to keep track of an atoms electrons!
i) Rules for Assigning Oxi
8. The Hydronium Ion
a) Acids release a proton (H+) when mixed with water!
HCl(g) H+(aq) + Cl-(aq)
b) What Happens to a Proton in Water?
i) H+ is very positive and is therefore strongly attracted to anything negative.
ii) H2O molecule has a negative part
3. Equilibrium Background
a) Reversible Reactions
i) Many reactions can go in reverse and have separate activation energies!
N2O4(g) is heated in a closed flask to form 2NO2(g) molecules
N2O4 + energy 2NO2
2NO2(g) molecules will then combine
1. Activation Energy
a) Ineffective Collisions
Not all collisions between reactants will result in products. If they do not
collide with enough "activation energy" (i.e.: not head on collision or not fast
enough), then the reactants will not react!
10. Reaction Mechanisms
The reactants might not all combine at once, but in fact, take a sequence of steps to reach
the product. Each step can also proceed at its own rate!
5. Equilibrium Calculations
Type 1 (system at equilibrium)
What is the Keq for the reaction 2HI (g)
H2 (g) + I2 (g) if there is
2.0 mol of HI, 3.0 mol of I2, and 3.5 mol of H2 in a 5.0L closed flask?
[H2] = 3.5/5 = 0.7 M
Keq = [H2][I2]
[I2] = 3/5 =
11. Reaction Profiles
Lets include everything we have learned: exothermic/endothermic, enthalpy,
activation energy and intermediates!
Example 1: Building the house reaction
Ea 2nd step
Ea 1 step
Ea 3rd step
8. Le Chateliers Principle
This principle explains how equilibrium works in a nutshell!
If a reaction in equilibrium is subjected to a change, the equilibrium will take
steps to counteract that change.
Le Chateliers principle is a tool we can use to predi
4. Equilibrium Calculations contd
Type 3 (system changing to equilibrium Calculating concentration of a species)
Example 1: 2A (g) + B (g)
An unknown amount of C was placed into a 3.0 L flask. When equilibrium was
reached, the concentration of A wa
7. Equilibrium Systems in Solutions
a) Whats Different with Solutions?
i) solutions at equilibrium will follow all we learned about Le Chateliers principle
and gases from previous, but there is a bit more info required for dealing with
6. What Causes an Equilibrium?
A reaction will either: 1. proceed forward
2. not proceed (proceed in reverse)
3. form an equilibrium.
i) The side of the reaction having the least enthalpy is favored.
ii) In other words, the exothermic reaction
9. Quantitative Equilibrium
a) Equilibrium Expression
i) we can quantify (attach a numerical value) the equilibrium for most reactions by
creating a ratio of products to reactants.
A + B
2. Enthalpy Changes
a) What is "Enthalpy"?
i) enthalpy is the total PE and KE of a reaction
ii) think of enthalpy as heat of reaction or energy of reaction
iii) symbol for enthalpy is H.
symbol for change in enthalpy is H
b) How does enthalpy apply to rea
4. Equilibrium Dissociation for Water, Acids and Bases
a) What is Dissociation of Water?
i) Liquid water is in equilibrium with its aqueous ions:
2H2O(l) + 59kJ
H3O+(aq) + OH-(aq)
ii) Kw = [H3O+] [OH-] = 1.00 x 10-14
iii) Water is neutral so: [H3O+] = [OH
2. Strength of Acids and Bases
a) What is a Strong Acid?
i) 100% dissociated in water
ii) No reverse reaction. Not in equilibrium.
HCl + H2O H3O+ +
(no undissociated HCl)
iv) There are six strong acids. Refer to Relative S
5. Ksp and Precipitate Formation
The value of Ksp is the point between the ions precipitating or the ions
At exactly Ksp, the ions will just start to precipitate. You have just arrived at
the saturation point.
a) Trial Ksp aka. The Ion
3. Arrhenius Theory of Acids and Bases
i) Release H+(aq) in water
ii) Any ionic species starting with H.
Eg.: HCl, HNO3
iii) Are electrolytes
iv) Taste sour
v) Turn Litmus paper red
vi) Produce H2(g) when react with most metals.
vii) Reacts with
1. Bronsted Lowry Theory of Acids and Bases
takes equilibrium reactions into account!
i) Proton donors gives H+ to another substance
ii) HCl + H2O
H3O+ + Cl-
HCl donated one proton to H2O, so it is an acid.
HCl is a Monoprotic Acid (donates on