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Final

CHEM105 Study Guide - Final Guide: Weak Base, Conjugate Acid, Rice Chart


Department
Chemistry
Course Code
CHEM105
Professor
Yoram Apelblat
Study Guide
Final

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Applications of Aqueous Equilibria
Common Ions, Buffers, titrations
Solution contains the weak acid and its salt
o The common ion is common to both the acid and the salt
o Adding a common ion decreases the percent dissociation of the
weak acid
A buffer must have acid component to react with OH- and basic
components to react with H+
o A buffer has the ability to resist changes in pH when strong
acids or bases are added
o Cannot be a strong acid or strong base because a neutralization
reaction would occur
o The ideal buffer contains equal amounts of a weak acid and its
conjugate weak base
o Adding a strong acid will increase the concentration of the
weak acid
o Adding a strong base will increase the concentration of the
weak base.
Titration problems
o Amount of strong acid (H3O+) = amount of weak acid formed
(HA) = amount of weak conjugate base reacted (A-)
o Amount of strong base (OH-) = amount of weak base formed
(A-) = amount of weak acid reacted (HA)
The difference between titration with a strong acid and a
strong base is which species increased or decreased in
moles.
o Keep in mind concentrations have changed because volume has
changed.
New concentration doesn`t necessarily have to be
calculated, just the new number of moles
o Henderson-Hasselbalch equation
Don’t need to know the concentration of H3O+ or OH-,
only the concentration of A- and HA
   

This equation can always be used after finding the
equilibrium concentration after the titration.
o For weak acid/ strong base and weak base/strong acid titrations,
treat the solution as a buffer.
At the halfway point, pH = pKa
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