Unit 3 Acids and Bases

UNIT 3 ACIDS AND BASES

Marissa LevyBoyi Zhang

Shana Zucker

WHAT IS AN ACID? WHAT IS A BASE?

ArrheniusAcid- An acid is a substance that when dissolved increases

H+ concentrationBase- A base is a substance that when dissolved increases

OH- concentration

Bronsted-LowryAcid- An acid is a substance that donates a protonBase- A base is a substance that accepts a proton

LewisAcid- An acid is a substance that is an electron-pair acceptorBase- A base is a substance that is an electron-pair donor

Brönsted - Lowry

Arrhenius

Lewis

CONJUGATE ACIDS AND BASES

What’s an acid and what is a base?NH3 + H20 ⇆ NH4+ + OH- Base Acid Conjugate Acid Conjugate Base

WHAT IS THE DIFFERENCE BETWEEN WEAK AND

STRONG?

Strong1. Disassociate2. Ionize completely

Weak1. Disassociate2. Ionize Partially3. Have Ka or Kb

values

STRONG SOLUTIONS AT EQUILIBRIUMHow do you calculate pH of a strong solution at equilibrium?

1.Write the equilibrium equation2.Whatever concentration you start

with is the concentration you end with

3.Calculate the pH

STRONG SOLUTIONS AT EQUILIBRIUMHow do you calculate pH of a strong solution at equilibrium?

0.25 M of HClO3 in water.

KOH(aq) + H20 (l) K⇆ + (aq) + OH- (aq)

.25 M 0 0-.25 M +.25 M +.25 M

0 .25 M .25 M

pOH= -log(.25)= .602 pH= 14- pOH= 13.40

WEAK SOLUTIONS AT EQUILIBRIUM

How do you calculate pH of a weak solution at equilibrium?

1.Write the equilibrium equation2.Write the ICE equation3.Solve for X4.Calculate the pH

WEAK SOLUTIONS AT EQUILIBRIUM

How do you calculate pH of a solution at equilibrium?’A 0.25 M Phosphoric solution is prepared in water.

Ka = 7.5 x 10-3

1. H3PO4 + H₂O (l) ⇆ H+ + H2PO4- Ka = 7.5 x 10-3

2.

3. 7.5 x 10-3 = x2/ .25 x= .0433

4. pH= -log(.0433)= 1.36

.25 M 0 0-x +x +x

.25 -x x x

TITRATION FORMULA

N1C1V1= N2C2V2

If 15.0 mL of HCN is completely titrated with 25.0 mL of 0.100 M NaOH calculate the concentration of HCN.

1(C1) (15.0)= 1(.100)(25.0)C1= .167 M

WRITING TITRATION EQUATIONSStrong Acid Strong BaseH+ + OH- ⇆ H₂O (l)

WRITING TITRATION EQUATIONS

Weak Acid Strong BaseH3PO4 + OH- ⇆ H₂O (l) + H2PO4

-

Weak Acid Weak BaseHF + N2H4 HN⇆ 2H4

+ + F-

WHAT IS A BUFFER?

Buffer1. A weak-acid base conjugate pair2. They resist changes in pH

CALCULATING PH OF A BUFFER

pH= pKa + log (base)/(acid)pOH= pKb + log (acid)/(base)

Sources http://chemistry.about.com/od/acidsbase

1/ss/titrationcurves_2.htm http://www.chemistry.wustl.edu/~

edudev/LabTutorials/Buffer/Buffer.html http://www.quickmeme.com/meme/36jbu

2/