Neutralization of Acids and Bases In general, a titration involves the addition of either a strong...

Neutralization of Acids and Bases

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?

Can further hydrolyzeto form acidic or basic

solutions

• Titrations

Standard Solution

Sample Solution

Burette

Unknown [ ]

Sample Solution

Known [ ]

Standard Solution

Primary Standard with a

precisely known [ ]

1st titration

2nd titration

?

Why a primary standard?• If NaOH is the standard solution, it’s [ ] may not be

accurate. Why?

• NaOH is hygroscopic (absorbs moisture in the air) which can affect its molar mass

• A primary standard is used to verify the [ ] of the “known” standard solution

• A primary standard must be:– Pure & stable– Non-hygroscopic– Have an accurately known molar mass

Choosing Indicators For Titrations

will depend on the overall pH of the salt produced

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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:__________________________________

HCl + NaOH H2O + NaCl

H+ + Cl- + Na+ + OH- H2O + Na+ + Cl-

H+ + OH- H2O

pH = 7 (neutral salt)

Bromothymol blue

Titration Curve for Strong Acid & Strong Base

pH of sample solution is

very low SA

Base is the standard solution being 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:

Monoprotic AcidsWhen the mole ratio of acid to bases is 1:1 in the balanced equation

(assuming that the concns are the same),

then they will require equal volumes to reach equivalence point

Acid and Base strength is irrelevant!!

Example: A 0.2 M strong acidstrong acid requires an equal volume of 0.2 M weak baseweak base to reach equivalence point if they have 1:1 ratio

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