C. Johannesson

I. Introduction toAcids & Bases

(p. 453 - 473)

I. Introduction toAcids & Bases

(p. 453 - 473)

Ch. 15 & 16 - Acids & BasesCh. 15 & 16 - Acids & Bases

C. Johannesson

A. PropertiesA. Properties

electrolytes electrolytes

turn litmus red

sour taste

react with metals to form H2 gas

slippery to touch

turn litmus blue

bitter taste

ChemASAP

vinegar, milk, soda, apples, citrus fruits

ammonia, lye, antacid, baking soda

C. Johannesson

B. DefinitionsB. Definitions

Arrhenius - In an aqueous solution:

HCl + H2O H3O+ + Cl–

• Acids form hydronium ions (H3O+) (by releasing hydrogen ions into the water)

H

HH H H

H

ClClO O

–+

acid base

C. Johannesson

B. DefinitionsB. Definitions

Arrhenius - In aqueous solution…

• Bases form hydroxide ions (OH-)

NH3 + H2O NH4+ + OH-

H

H

HH H

H

N NO O–+

H

H

H H

base acid

C. Johannesson

B. DefinitionsB. Definitions

Brønsted-Lowry Definitions:

HCl + H2O Cl– + H3O+

• Acids are proton (H+) donors. • Bases are proton (H+) acceptors.

conjugate acidconjugate base

baseacid

C. Johannesson

B. DefinitionsB. Definitions

H2O + HNO3 H3O+ + NO3–

CBCAAB

C. Johannesson

B. DefinitionsB. Definitions

NH3 + H2O NH4+ + OH-

CA CBB A

C. Johannesson

B. DefinitionsB. Definitions

Amphoteric - can be an acid or a base. Monoprotic- an acid that can only donate

one H+

Polyprotic - an acid that can donate more than one H+

C. Johannesson

C. StrengthC. Strength

Strong Acid/Base• 100% ionized in water• strong electrolyte

- +

HCl

HNO3

H2SO4

HBr

HI

HClO4

NaOH

KOH

Ca(OH)2

Ba(OH)2

Acid StrengthAcid Strength

Ternary:• Strong if # oxygen - # hydrogen ≥ 2

• H2SO4

• HNO3

• Weak if not!• H2SO3

• HNO2

LPChem:Wz

Acid StrengthAcid Strength

Binary:• Strong if HCl, HBr, HI• Weak if not!

• H2O

• HF

LPChem:Wz

Base StrengthBase Strength

Bases generally have the formula MOH, where M is a metal:• Strong if M is from Group 1 or “heavy

Group 2” (bottom of Gr2)

• Li, Na, K, Rb, Cs, Fr & Ca, Sr, Ba• Weak if not!

• Mg(OH)2

• AgOHLPChem:Wz

C. Johannesson

C. StrengthC. Strength

Weak Acid/Base• does not ionize completely• weak electrolyte

- +

HF

CH3COOH

H3PO4

H2CO3

HCN

NH3

Strong vs. WeakStrong vs. Weak

Electrolyte:• Conductive in aqueous solution.

Why do we need electrolytes?• Muscle contractions are controlled by

electrical messages of the nervous system. • You sweat out electrolytes during a workout. • They need to be replaced to keep things

working. • And to prevent muscle cramps (from

insufficient electrolyte levels).

LPChem:Wz

- +

Strong vs. WeakStrong vs. Weak

“Strong” substances (both acid and base) dissociate strongly.Dissociate = break into ions

• Acid: HA H+ + A-

• Base: MOH M+ + OH-

Notice the arrows!• These reactions go to completion.

LPChem:Wz

Strong vs. WeakStrong vs. Weak

These reactions go to completion.• This means that a solution of the

“strong acid” HCl doesn’t actually contain any HCl molecules.

• HCl H+ + Cl-

• All the HCl molecules dissociated.• Now it is a solution of H+ and Cl- ions.

(We still label it “HCl” but it’s really H+ + Cl-)

LPChem:Wz

Strong vs. WeakStrong vs. Weak

“Weak” substances (both acid and base) dissociate weakly.

• Acid: HA H⇌ + + A-

• Base: MOH M⇌ + + OH-

Notice the arrows!• These reactions DO NOT go to completion. They are at equilibrium.

LPChem:Wz

Strong vs. WeakStrong vs. Weak

Weak DO NOT go to completion.• This means that a solution of the

“weak acid” HF contains a mixture of HF molecules and H+ and F- ions.

• HF ⇌ H+ + F-

• Only a fraction of the HF molecules dissociated. Now the solution is a mixture of HF molecules, H+ ions and F- ions.

LPChem:Wz

Strong vs. WeakStrong vs. Weak

End result:Strong Acids & Bases dissociate all the

way (making all ions)• and are therefore strong electrolytes

Weak Acids & Bases dissociate part way ⇌ (making only some ions)

• And are therefore weak electrolytes.

LPChem:Wz