Neutralization of Acids and Bases

• Titrations

Standard Solution

Sample Solution

Burette

Primary Standard with a

precisely known [ ]

Unknown [ ]

Sample Solution

Known [ ]

Standard Solution

1st titration

2nd titration

In general, a titration involves the addition of either a strong acid, strong base or both (must go to completion) as follows:

ACID + BASE WATER + SALT

• Titrations do not always yield an equivalence point with a pH of 7. Why?

The salts produced may further hydrolyze to change the equivalence to either acidic or basic

Choosing Indicators For Titrations

will depend on the overall pH of the salt produced

Strong Acids and Strong Base Titrations

Example: HCl (strong acid) and NaOH (strong base)

Formula Equation:__________________________________

Complete Ionic Equation: ____________________________

Net Ionic Equation:__________________________________

pH at equivalence point: _____________________________

Possible Indicators:__________________________________

Titration Curve for Strong Acid & Strong Base

pH of sample solution is

very low SA

Base is the standard solution being added

Strong Acid & Strong Base

1

4

3

2

How are the pH’s calculated at the various stages?Eg. 40.0 mL of 0.100 M HCl is titrated with 0.100 M NaOH.

1 The initial acid concentration?

2 NaOH is added (eg. 30.0 mL) but acid is in excess?

3 Equivalence point?

4 Base is in excess (eg. 50.0 mL added)?

Example: CH3COOH (weak acid) and NaOH (strong base)Formula Equation:__________________________________Complete Ionic Equation: ____________________________Net Ionic Equation:__________________________________pH at equivalence point: _____________________________Possible Indicators:__________________________________

Weak Acids and Strong Base Titrations

Weak Acid & Strong Base

pH starts higher as CH3COOH is

a weaker acid

E.P > 7

Weak Base and Strong Acid Titrations

Example: NH3 (weak base) and HCl (strong acid)Formula Equation:__________________________________Complete Ionic Equation: ____________________________Net Ionic Equation:__________________________________pH at equivalence point: _____________________________Possible Indicators:__________________________________

Weak Base & Strong Acid

Standard Acid is added

Sample of Strong Base

E.P < 7

Three types of Titrations:

Reactants Salt Formed is… pH at Equivalence Point

Strong Acid – Strong Base Neutral = 7.00 Weak Acid – Strong Base Basic > 7.00 Strong Acid – Weak Base Acidic < 7.00

Choosing an Indicator:Indicators can be used to tell you when you have reached the Equivalence (Stoichiometric) Point in a Titration. Ideally, the pH at the Transition Point (pKa) of the Indicator will be the same as the pH at the Equivalence Point of the titration. Or:

pKa (indicator) = pH at EP of Titration

Monoprotic Acids

When the mole ratio of acid to bases is 1:1,

then they will require equal volumes to reach equivalence point

Acid and Base strength is irrelevant

Example: A strong acid requires an equal volume of weak base

to reach equivalence point if they each have a coefficient of 1

Polyprotic Acids

When an acid releases more than one proton, ie. H2SO4,

then they will require twice the volume of base to

reach equivalence point

Titration of a polyprotic acid:one equivalence point per acidic hydrogen