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Acids and Bases. Arrhenius Acids and Bases
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PREVIEW

2. Show the chemical reaction to which Ka applies for H2PO41-

4. Determine the Kb value for HPO42-.

5. Which direction is the reaction favored?

Slide 38

Acid-Base Reactions of Salts (Ions as Acids and Bases)

Acid-Base Reactions of Salts (Ions as Acids and Bases)

A. Salts

1. Ionic compounds (salts) formed from acid-base reaction.

HA + MOH  M+A- + H2O

acid base salt

2. The salt (MA) could leave the resulting aqueous solution to be neutral, acidic, or basic.

Slide 39

B. Hydrolysis of Salts

B. Hydrolysis of Salts

Salts may react with water (hydrolysis reaction involving the splitting of a water molecule) to produce acidic or basic solutions.

For hypothetical ionic compound MA, consisting of

Mx+ cation and Ax- anion, consider possible

hydrolysis reactions and possible consequences:

Mx+ + H2O  M(OH)(x-1)+ + H+ acidic solution

Ax- + H2O  HA(x+1)- + OH- basic solution

If both cation and anion hydrolyze, compare Ka and Kb

Slide 40

C. Predicting If Hydrolysis Occurs

C. Predicting If Hydrolysis Occurs

1. Write the hypothetical hydrolysis rxns for salt.

(one for cation and one for anion)

2. Look at the hypothetical hydrolysis products.

3. If a strong acid or strong base was hypothetically

produced, these hydrolysis reactions DO NOT

occur. No acid or base properties upon

hydrolysis. Recall Table of Strong Acids and Bases

4. If a weak acid or base was produced, these hydrolysis reactions DO occur and produce acid or base properties. For hydrolysis products:

H+ : acidic OH- : Basic

Slide 41

D. Example Problems

D. Example Problems

Will an aqueous solution of the salt be acidic,

basic, or neutral?

1) NaCl

2) NH4Cl

3) NH4CN

Slide 42

Cumulative Example Problem

Cumulative Example Problem

The cyanate ion, OCN-, is a weak base. The Ka for HOCN (cyanic acid) is 3.4 x 10-8. Calculate the pH of a 0.200 M solution of NaOCN.

Slide 43

Lewis Acids and Bases

Lewis Acids and Bases

A. Some Acid-Base Reactions Do Not Fit

Either Arrehenius or Bronsted –Lowry

Definitions.

Consider:

HCl + NaOH  NaCl + H2O

Al3+ + 6 H2O  Al (H2O)63+

Slide 44

B. Lewis Acids and Bases

B. Lewis Acids and Bases

1. Lewis Acid: electron pair acceptor

(Accepts a pair of electrons to form a new bond)

** Usually has an incomplete octet of electrons

2. Lewis Base: electron pair donor

(Donates a pair of electrons to form a new bond)

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