Acids and Bases

Ch 16

I. Properties of Acids and Bases

• A. Acids– 1. Taste sour (think

lemons: citric acid)– 2. React with metals to

produce hydrogen– 3. Conduct electricity

• B. Bases– 1. Taste bitter (think

Milk of Magnesia)– 2. Feel slippery (like

soap)– 3. Conduct electricity– 4. Can be caustic

C. The Arrhenius Model

• 1. Svante Arrhenius was 1st person to recognize the properties of acids and bases.– a. Arrhenius Acid- produces H+ ions in solution

• HCl(aq) → H+(aq) + Cl-(aq)– b. Arrhenius Base- produces OH- ions in solution

• NaOH(aq) → Na+(aq) + OH-(aq)

D. Brønsted- Lowry Model

• 1. Johannes Brønsted and Thomas Lowry developed a more general definition of acids and bases.– a. Brønsted- Lowry acid- a proton (H+) donor– b. Brønsted- Lowry base- a proton (H+) acceptor– c. Conjugate base- the remaining substance after

an acid has donated its proton– d. Conjugate acid- the remaining substance after a

base has accepted a proton.

Example• HCl(aq) + H2O(aq) → H3O+(aq) + Cl-(aq)

BL acid BL base Conj Conj acid base

• HSO4-(aq) +H2O(aq) → H2SO4(aq) + OH-(aq)

BL base BL acid Conj Conj acid base

H3O+ is called the hydronium ion.

Problems to try

• 1. Which of the following represent conjugate acid-base pairs?– a. HF, F- b. NH4

+, NH3 c. HCl, H2O

• 2. Write the conjugate base for each of the following:– a. HClO4 b. H3PO4 c. CH3NH3

+

C. Acid Strength

• 1. strong acids and bases: break apart 100% into their ions in solution

• 2. weak acids and bases: only 5% breaks down into ions in solution.

Hydronium Ion Concentration

• [H3O+]

– It’s sometimes written as [H+] as a short cut, because we are just concerned about the H.

• Tells how concentrated the acid/ base is in terms of MOLARITY!!!!!

pH

• pH gives the relative strength of an acid or base!

• pH = -log [H+]• pOH = -log [OH-]• pH + pOH = 14• [H+] • [OH-] = 1 × 10-14

• 3. Strong Acids– a. have weak conjugate bases– HClO4

– HI– HBr– H2SO4

– HCl– HNO3

– b. Diprotic acids- an acid that can give 2 protons• H2PO4(aq) → H+(aq) + HPO4

-(aq)

– HPO4-(aq) → H+(aq) + PO4

2-(aq)

– c. Triprotic acids- an acid that can give 3 protons• H3PO4(aq) → H+(aq) + H2PO4

-(aq)

– H2PO4-(aq) → H+(aq) + HPO4

2-(aq)

» HPO42-(aq) → H+(Aq) + PO4

3-(aq)

4. Strong BasesHave a weak conjugate acid

Alkali Metal Hydroxides• NaOH• KOH• LiOH• RbOH• CsOH

Alkaline Earth Metal Hydroxides

• Ca(OH)2

• Ba(OH)2

• Sr(OH)2

• While these 3 are strong bases, they are not very soluble in water.