Chapter 14

Acids and Bases

Some Properties of Acids

Produce H+ (as H3O+) ions in water (the hydronium ion is a

hydrogen ion attached to a water molecule)

Taste sour

Corrode metals

React with bases to form a salt and water

pH is less than 7

Turns blue litmus paper to red “Blue to Red A-CID”

Some Properties of Bases

Produce OHProduce OH-- ions in water ions in water

Taste bitter, chalkyTaste bitter, chalky

Feel soapy, slipperyFeel soapy, slippery

React with acids to form salts and waterReact with acids to form salts and water

pH greater than 7pH greater than 7

Turns red litmus paper to blue “Turns red litmus paper to blue “BBasic asic BBlue”lue”

Acid/Base Definitions

• Brønsted – LowryBrønsted – Lowry

Acids – proton donorAcids – proton donor

Bases – proton acceptorBases – proton acceptor

A “proton” is really just a hydrogen A “proton” is really just a hydrogen atom that has lost it’s electron!atom that has lost it’s electron!

LecturePLUS Timberlake 5

Bronsted-Lowry Acids

Acids are hydrogen ion (H+) donors

Bases are hydrogen ion (H+) acceptors

HCl + H2O H3O+ + Cl-

donor acceptor + -

+ +

Reactions of acids

Copy the 7 reactions from pg 319

Conjugate pairs

acidconjugate

basebase conjugate

acid

An acid and a base which differ only by the presence or absence of a proton (H+ )are called a conjugate acid-base pair. One half of the pair is always on the left-hand side of the equation, the other on the right-hand side.

The stronger an acid, the weaker its conjugate base, and, conversely, the stronger a base, the weaker its conjugate acid.

Conjugate PairsConjugate Pairs

Example 3.1For each of the following acid/base reactions, link the conjugate acid/base pairs:

a) HCl (aq) + H2O (l) ----> H3O+ (aq) + Cl- (aq)b) H2SO4 (aq) + H2O (l) ----> HSO4

- (aq) + H3O+ (aq)c) NH3 (g) + H2O (l) ----> NH4

+ (aq) + OH- (aq)d) H3O+ (aq) + OH- (aq) -----> 2 H2O (l)

 

Learning Check!

Ans.

Solutionacid/base base/acid

 a) HCl (aq) / Cl- (aq) H2O (l) / H3O+ (aq)b) H2SO4 (aq) / HSO4

- (aq) H2O (l) / H3O+ (aq)c) H2O (l) / OH- (aq) NH3 (g) / NH4

+ (aq)d) H3O+ (aq) / H2O (l) OH- (aq) / H2O (l)

HNO3, HCl, HBr, HI, H2SO4 and HClO4 are the strong acids.

Strong and Weak Acids/BasesStrong and Weak Acids/Bases

The strength of an acid (or base) is determined by the amount of IONIZATION.

The strength of an acid (or base) is determined by the amount of IONIZATION.

Strong Acid Weak Acid

15.4

STRENGTH OF ACIDS AND BASES

The strength of an acid or base is determined by its percent dissociation/ionization in water.

All strong acids and bases dissociate/ionize completely, 100%.

• Hydrohalic acids: HCl, HBr, HI

• Nitric acid: HNO3

• Sulfuric acid: H2SO4

• Perchloric acid: HClO4

Strong AcidsStrong Acids

• *One of the best known is acetic acid CH*One of the best known is acetic acid CH33COCO22HH

Weak AcidsWeak Acids

•

Common strong bases Common strong bases include include NaOH ,NaOH ,KOH andKOH and Ca(OH)Ca(OH)22..

CaOCaO

Strong BasesStrong Bases

Strong bases areStrong bases are (—OH), oxides of 1A and 2A metals (except Mg and Be), H-, and .

One of the best known weak bases is ammoniaOne of the best known weak bases is ammonia

NHNH3 3 (aq) + H(aq) + H22O (l) O (l) ↔↔ NH NH44+ + (aq) + OH(aq) + OH- - (aq)(aq)

Weak BasesWeak BasesWeak BasesWeak Bases

Polyprotic and amphiprotic

• A polyprotic acid is one which is capable of donating more than one proton.

• A polyprotic base is one which is capable of accepting more than one proton.

• An amphiprotic (amphoteric) substance can act as either an acid or a base.

•  

Amphiprotic substances

• Examples

• Water acts as a base in its reaction with HCl and as an acid in its reaction with NH3.

• NH3(aq) + H2O(l) NH4(aq) + OH–(aq)➝• HCl(g) + H2O(l) H3O+(aq) + Cl–(aq)➝