ACIDS AND BASES

• Distinguish between strong and weak acids and bases.

Include: electrolytes and non-electrolytes

Additional KEY Termsconcentrated dilutemonoprotic diprotic

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 hydrogen in a very polar bond is ionizable

(H must be bonded to a very electronegative element)

Cl HH

O

H

H H

H

H

C C

+ +

δ+δ-

δ+

δ-++-

Electrolytes are classified as strong OR weak Strong: produces many ions in solution.

• dissociates 100% in water (NaCl)

Weak: partially dissociates (<<100%) in solution.• usually weak polar molecules (vinegar)

A (s) B+(aq) + C–

(aq)

ionic polar

ionic polar

• easily donate protons • completely dissociate or ionize

Strong acids are 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 weak electrolytes:

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.

• incompletely ionize• equilibrium reached between ions and acid

Indicate equilibrium using reversible arrow

Name of Weak Acid Formula

carbonic acid H2CO3

hydrofluoric acid HF

acetic acid HC2H3O2

phosphoric acid H3PO4

Strong bases are strong electrolytes:

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

(aq)

water

Indicate complete dissociation using single arrow.

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

• easily accept protons • completely dissociate into OH-, or oxide, (O-2)

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

NH3(g) + H2O (l) NH4+

(aq) + OH-(aq)

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

Weak bases are weak electrolytes: • incompletely ionize• equilibrium reached between ions and base

Indicate equilibrium using reversible arrow

Common weak bases are usually conjugate bases of strong acids.

In fact: The stronger the A/B, the weaker its conjugate.

The weaker the A/B, the stronger its conjugate.

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

THOUGHTS:

• 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

HA H+ + A-

HA + H2O H3O+ + A-

Strong Acid

Weak Acid

HA + H2O + A-

H+ H2O

H3O+

9.0 M 1.0 M 1.0 M[E]+x+ x- x[C]

0010 M[I]

0 2.5 M 2.5 M[E]

+x+ x- x[C]002.5 M[I]

CAN YOU / HAVE YOU?

• Distinguish between strong and weak acids and bases.

Include: electrolytes and non-electrolytes

Additional KEY Termsconcentrated dilutemonoprotic diprotic