ANNOUNCEMENTSANNOUNCEMENTS

Final Exam: Friday, May 14th at 8:00 amWhat to Bring: Calculator

No. 2 PencilsTwo pages of notes

Format: Multiple choice (scantron)

Review Session: Wednesday, May 12th at 10:00amIRC 3

Predicting the acid-base behavior Predicting the acid-base behavior of a saltof a salt

Look at cation and anion:Determine if acid, base, or pH-neutral

If cation/anion are…Salt behaves as…

Effect on pH

pH-neutral pH-neutral pH-neutral none

pH-neutral acid acid lowers pH

pH-neutral base base raises pH

acid base If Ka>Kb, acid lowers pH

If Ka<Kb, base raises pH

How to determine the pH of a salt How to determine the pH of a salt solutionsolution

1. Determine whether the salt behaves as an acid or a base

2. Write the equation for the acid or base

3. Set up ICE table and K expression. Solve for [H3O+] or [OH-].

4. Convert [H3O+] or [OH-] to pH.

The strength of an acid is The strength of an acid is dependent on bond strength and dependent on bond strength and electronegativityelectronegativity

H-A → H+ + A-

To act as an acid, two things must happen:1. H-A bond must break

2. “A” takes both electrons to make “A-”

Acid strength examplesAcid strength examples

HNO2 vs. HNO3

Acetic vs. Trifluoroacetic Acid

QUIZ TIME!QUIZ TIME!Answers will be posted online after class today for your review.

Lewis acid◦ Accepts electron

pair◦ Must have an

incomplete octet

◦ Example: BF3

Lewis Base◦ Donates electron

pair◦ Anything with

lone pair can be Lewis base

◦ Example: NH3

Lewis Acids and Bases swap Lewis Acids and Bases swap electron pairs instead of protonselectron pairs instead of protons

The lone pair from the Lewis base is used to form a new bond.

Is water a Lewis acid or base?Is water a Lewis acid or base?

Can water be a ….◦Brønsted acid?◦Lewis acid?◦Brønsted base?◦Lewis base?

Lewis Acid ExamplesLewis Acid Examples

Nonmetal oxides are unusual Lewis Nonmetal oxides are unusual Lewis acidsacidsCarbon dioxide in water

consumes OH-, leaving water acidic (H3O+ > OH-)

Which of the following mixtures are buffers?

◦ HCl + NaCl

◦ CH3CO2H + NaCH3CO2

◦ NH3 + NH4Cl

◦ NaOH + HCl

A buffer is a mixture of a weak acid A buffer is a mixture of a weak acid and its conjugate baseand its conjugate base

Buffers resist changes in pH by Buffers resist changes in pH by “soaking up” H“soaking up” H++ or OH or OH-- ions ionsExample:

NH4+/NH3 buffer

◦when acid is added:

◦when base is added:

Review Session:Wednesday at 10am

Final Exam:Friday at 8am

Good luck on finals!