Lecture 12

Question 1

What makes a molecule acidic or not ? (lower pH)

Answer 1

Acidic –> p+ can fall off

1. Bond strength
   –> lower = more acidic
2. Bond polarity
   –> higher = more acidic (easier for p+ to fall off
3. Size
   –> larger = more acidic
4. # of O around central atom–> more O = more acidic (higher electronegativity SO higher polarity)

Question 2

What is the difference when solutions of acids/bases contain a common ion

Answer 2

Common ion effect!
–> Solution won’t go as far as usual (since there is already some product in the beginning)
–> P doesn’t start at 0!!

Question 3

How does the common ion effect affect the % dissociation?

Answer 3

It reduces it

Question 4

What is a buffer

Answer 4

• Compound that fights against pH change (ex: blood)
• Buffered solution: solution that resists a change in
  pH
• Strong acid/base added is removed and converted into something weaker

NOTE: if too acidic or too basic, buffer fails

Question 5

How to identify a buffer

Answer 5

Contains weak acid/weak base and its salt (common ion) (MUST HAVE BOTH)

Question 6

How to do buffer problems

Answer 6

1. Find initial pH (Ka –> [H+] –> pH)
   –> use ICE of weak acid/weak base and common
   ion (salt)
2. Add strong base/strong acid to buffered soln (spike)
3. Identify major species (with added strong acid/base)
4. FIGHT TO THE DEATH (to get new INITIAL [ ] after spike)
   –> between strong base/acid and weak base/acid
   –> FIGHT IN MOLES (use concentration x volume)
   –> BR (before reaction)
   AF (after reaction)
   C (concentration)
   –> one of the two goes to 0 (one with least amount of moles)
5. Use ICE to get new [ ] at eq
6. Find new pH from new [ ]