ACIDS AND BASES

HA + H2Obaseacid

H3O+ + A-

Con. baseCon. acid

B + H2Obase acid

BH+ + OH-

Con. baseCon. acid

For a solution to conduct an electric current, charged particles or ions must be present in the solution.

Electrolytes - conduct an electric current when in aqueous solution or when in a molten state.

All ionic compounds act as electrolytes (as do highly polar molecular compounds).

Most molecular compounds are non-electrolytes.

NaCl(s) Na+(aq) + Cl–

(aq)

C11H22O11(s) C11H22O11(aq)

non-electrolytes

electrolytes

Only hydrogens in very polar bonds are ionizable.

(H must be bonded to a very electronegative element).

Phosphoric acid

H

O

OHO

O

sp

Cl H

H

O

H

H H

H

H

C C

+ +

δ+δ-

δ+

δ-

δ+

δ-

+

+

+-

Electrolytes are classified as strong and weak. A strong electrolyte is one which produces many ions in solution - dissociate 100% in water. (NaCl)

A weak electrolyte only partially dissociates. Usually polar covalent molecules. (household vinegar)

A (s) B+(aq) + C–

(aq)

Strong acids are substances that easily donate protons - completely dissociate or ionize in water.

Strong acids are usually strong electrolytes.

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

(aq)water

Indicate complete dissociation using single arrow.

[HCl]i = [H+]e = [Cl-]e

Name of Strong Acid Formula

perchloric acid HClO4

hydrochloric acid HCl

sulfuric acid H2SO4

nitric acid HNO3

hydroiodic acid HI

hydrobromic acid HBr

Weak acids are poor or weak electrolytes.

Weak acids ionize incompletely.

This establishes an equilibrium between the ions and the molecules of acid.

HC2H3O2 + H2O H3O+ + C2H3O2-

acetic acid

The reverse reaction is favored over the forward one. The ions formed react very easily to reform the acid and the water.

Name of Weak Acid Formula

carbonic acid H2CO3

hydrofluoric acid HF

acetic acid HC2H3O2

phosphoric acid H3PO4

Strong bases are strong electrolytes.

Strong bases usually dissociate into OH¯, or oxide ions, (O-2).

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

(aq)water

Indicate complete dissociation using single arrow.

[NaOH]i = [Na+]e = [OH-]e

Basically, any hydroxide and Alkali (1A) or Alkali-Earth Metal (2A) would be a strong base because of 100% dissociation.

Name of Base Formula

barium hydroxide Ba(OH)2

strontium hydroxide Sr(OH)2

lithium hydroxide LiOH

Weak bases are poor proton acceptors.

Do not dissociate completely - form an equilibrium between the molecule and the ions formed.

NH3(g) + H2O (l) NH4+

(aq) + OH-(aq)

Does not produce hydroxide ions readily. The reverse reaction is favored.

Common weak bases are usually conjugate bases of strong acids.

In fact: The weaker the acid, the stronger its conjugate

base.The weaker the base, the stronger its conjugate

acid.

HA + H2Obaseacid

H3O+ + A-

Con. baseCon. acid

weak

Acid Strength Table

Any acid that contains only one ionizable hydrogen is called monoprotic.

Contains two ionizable hydrogens - diprotic

Three - triprotic

Cl H

H

O

O

HO

O

s

H

O

O

HO

O

sp

H

Sulfuric acid

Phosphoric acid

Acid Strength Table

The equilibrium reaction favours the strongest acid.

HCO3– + PO4

3–

Which direction is favoured and why?

HCO3– + PO4

3– CO32– + HPO4

2–

acid1 base2 C base1 C acid2

fwd reaction is favouredHCO3

– is the stronger acid

Don't confuse weak and strong with dilute and concentrated.

Weak and strong indicates the proportion of an acid or base which ionized.

Dilute and concentrated refer only to the volume of acid and base dissolved in a total solution volume.

It is possible to have a concentrated weak acid/base or dilute strong acid/base

· Strong acids and bases are strong electrolytes. · Weak acids and bases are weak electrolytes.

· Weak acids and bases partially ionize in water.

· The stronger the acid, the weaker its conjugate base. · The stronger the base, the weaker its conjugate acid.

· When acids and bases react, the stronger acid donates its proton and the stronger base accepts the proton.