Acids & BasesChapter 14

2

Arrhenius Concept: Acids produce H+ in solution, bases produce OH ion. In aqueous solutions.

Brønsted-Lowry: Acids are H+ donors, bases are proton acceptors. This is the more general definition and can include solids and gases.

There are two ways to view Acids & Bases:

The Two Views

ArrheniusArrhenius - In aqueous solution…

HCl + H2O H3O+ + Cl–

• Acids form hydronium ions (H3O+)

H

HH H H

H

ClClO O

–+

acid

ArrheniusArrhenius - 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

Brønsted-LowryBrønsted-Lowry

HCl + H2O Cl– + H3O+

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

conjugate acidconjugate base

baseacid

Lewis Acid and BasesLewis

• Acids are electron pair acceptors. • Bases are electron pair donors.

Lewis base

Lewis acid

Properties

electrolytes electrolytes

turn litmus red

sour taste

react with metals to form H2 gas

slippery feel

turn litmus blue

bitter taste

ChemASAP

vinegar, milk, soda, apples, citrus fruits

ammonia, lye, antacid, baking soda

StrengthStrong Acid/Base

100% ionized in waterstrong electrolyte

- +

HCl

HNO3

H2SO4

HBr

HI

HClO4

NaOH

KOH

Ca(OH)2

Ba(OH)2

StrengthWeak Acid/Base

• does not ionize completely

• weak electrolyteHF

CH3COOH

H3PO4

H2CO3

HCN NH3

Strength

Ka =[H3O+][A-] [HA]

Acid Dissociation Constant (Ka): expression for the dissociation of an acid (larger value = stronger acid)

Kb = [HB+][OH-]

[B]

Base Dissociation Constant (Kb): expression for the dissociation of an base (larger value = stronger base)

Strength

Polyprotic AcidsSome compounds have more than 1 ionizable hydrogen.HNO3 nitric acid - monoproticH2SO4 sulfuric acid - diprotic - 2 H+

H3PO4 phosphoric acid - triprotic - 3 H+

Having more than one ionizable hydrogen does not make the acid stronger!

Hydrogen Ions from WaterWater naturally ionizes, or breaks into ions:

H2O ® H+ + OH-

This is the “self ionization” of water, and occurs to a very small extent:

[H1+ ] = [OH1-] = 1 x 10-7 M

Brackets [ ] mean “concentration of”

Hydrogen Ions from WaterH2O ® H+ + OH-

Since the [H+] and [OH-] equal, a neutral solution results from water

[H+] x [OH-] = 1 x 10-14 M2

Molarity is squaredThis is true of ALL solutions.As [H+] increases, [OH-] decreases

pH & pOH

pH = -log[H+] pOH = -log[OH-]

pH + pOH = 14.00

Acid – Base Neutralization

Rules for Acid-Base Reactions

1. List the species present in the combined solution and decide what reaction will take place (remember solubility!)

2. Write the balanced equation3. Calculate the moles of reactants (for solutions use

the volumes to convert to moles)4. Determine a limiting reactant if necessary5. Calculate the moles required of reactant or product

(in this case H+ or OH-)6. Convert to grams or volume as required

TitrationTitration: delivery of a measured volume of solution of a known concentration (titrant) to a substance being analyzed (analyte).

Equivalence Point: where enough titrant has been added to react completely with the analyte (marked by an indicator)Endpoint: point where the indicator changes color