To understand two models of acids and bases

Section 16.1

Properties of Acids and Bases

1. To understand two models of acids and bases

2. To understand how acids and bases ionize/dissociate in water

Learning Goals

Section 16.1


Acidic solutions have sour taste (tartness).

Ex.: citric acid in lemons, limes, oranges; acetic acid in vinegar

Basic (alkaline) solutions have bitter taste and are slippery.Ex.: soaps, “draino,” many

household cleaning products

Section 16.1


Acid, Base or Salt?

NaCl

NaOH

Ba(OH)2

HNO3

H2SO4

CaO

HCl

Mg(OH)2

NH3

LiOH

LiF

Section 16.1


Remember that… (add this to your notes)

Acid + Base Water + Salt

Ex.: HCl + NaOH H2O + NaCl

Acid-Base Reactions (review)

This is a double replacement reaction

Because H+ and OH- H2O

This is a neutralization reaction

Section 16.1

Properties of Acids and Bases Naming Acids (review)

If anion does NOT contain oxygen If anion contains oxygen

Prefix hydro-

Suffix –ic

attached to root name of element

suffix –ic if anion ends with –ate

suffix –ous if anion ends with –ite

attached to name of central element of anion / anion name

The following compounds dissolve in water to form acids:

HCl (hydrogen chloride) hydrochloric acid

HCN (hydrogen cyanide) hydrocyanic acid

H2S (dihydrogen sulfide) hydrosulfuric acid

Acid Anion Name

H2SO4 sulfate sulfuric acid

H3PO4 phosphate phosphoric acid

H2SO3 sulfite sulfurous acid

HNO2 nitrite nitrous acid

Section 16.1


A. Acids and Bases – Two Models

• Acid – produces hydrogen ions (H+) in aqueous solution

H2O

HCl(s) H+(aq) + Cl- (aq)

• Base – produces hydroxide ions (OH-) in aqueous solution H2O

NaOH(s) Na+(aq) + OH-(aq)

The Arrhenius Model (older) – Dissociation Reactions

Section 16.1


A. Acids and Bases – Two Models

• Acid – proton donor • Base – proton acceptor • The general reaction for an acid dissolving in water is

The Bronsted-Lowry Model (newer) – Dissociation & Reaction with Water

Section 16.1


A. Acids and Bases

The Bronsted-Lowry Model

• Water acts as a base accepting a proton from the acid.

• Forms hydronium ion (H3O+)

Section 16.1


A. Acids and Bases


• Water acts as an acid, donating a proton to the base. • Forms water molecule

NaOH + H2O Na+ + OH- + H2O

H+

Section 16.1


Ammonia is a base because it accepts a proton and becomes the ammonium ion:

NH3 + H+ NH4+

Ammonia ammonium, a polyatomic cation

Section 16.1


A. Acids and Bases


• Conjugate acid-base pairs

Section 16.1


The Bronsted-Lowry Model - Identifying Acid-Base Pairs

Do the two substances differ by a single proton?

HF, F- conjugate pair:HF H+ + F-

NH4+, NH3 conjugate pair:

NH4+ H+ + NH3

HCl, H2O not a conjugate pair:

Conj. base of HCl: Cl-

Conj. acid of H2O: H3O+

Section 16.1


The Bronsted-Lowry Model - Writing Conjugate Bases

The acid and its conjugate base must differ by a single proton.

Acid proton + conjugate base

1. HClO4 H+ + ClO4-

2. H3PO4 H+ + H2PO4-

3. CH3NH3+ H+ + CH3NH2

Section 16.1


Try to show the dissociation of each acid below into a proton and a conjugate base.

Acid proton + conjugate base

1. H2CO3 H+ + HCO3-

2. H3BO3 H+ + H2BO3-

3. H3PO3 H+ + H2PO3

-

4. HNO2 H+ + NO2-

Section 16.1


To understand the concept of acid strength

Learning Goals

Section 16.1


B. Acid Strength

• Strong acid – completely ionizes / dissociates• Forward reaction predominates

• Weak acid – most of the acid molecules remain intact

Section 16.1


B. Acid Strength

Section 16.1


B. Acid Strength

• A strong acid contains a relatively weak conjugate base.

• Water molecules compete with the base for the protons: a weak base loses (dissociation happens, strong acid), a strong base wins (little dissociation, weak acid)

Section 16.1


B. Acid Strength

• Common strong acids are

– Sulfuric acid, H2SO4

– Hydrochloric acid, HCl

– Nitric acid, HNO3

– Perchloric acid, HClO4

* Strong acids are strong electrolytes

good conductivity *

Section 16.1


B. Acid Strength / Acid Types

• Oxyacid – acidic proton is attached to an oxygen atom

– Typically a weak acid

• Organic acid – have a carbon atom backbone and commonly contain the carboxyl group

Section 16.1


Acid Strength / Acid Types

• Monoprotic acids can furnish only one proton.Ex.: HCl H+ + Cl-

• Diprotic acids can furnish two protons.Ex.: H2SO4 2H+ + SO4

2-

• Hydrohalic acids contain H attached to a halogen.Ex.: HCl (strong), HF (weak)

Section 16.1


B. Acid Strength

To understand two models of acids and bases

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