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
yellowyellow blueblue
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