ACIDS AND BASES
· Define electrolyte and explain the association with weak and strong.
· Explain the difference between weak and strong acid and base.
· Explain and compare dilute and concentrated solutions of acid or base.
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).
Cl HH
O
H
H H
H
H
C C
+ +
δ+δ-
δ+
δ-++-
Electrolytes are classified as strong and weak. Strong: produces many ions in solution - dissociates 100% in water. (NaCl)
Weak: partially dissociates. Usually weak polar molecules. (household vinegar)
A (s) B+(aq) + C–
(aq)
ionic polar
ionic polar
Strong acids 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.
Weak acids incompletely ionize.
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 dissociate into OH¯, or oxide, (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.
Incompletely dissociate - 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
HA H+ + A-
HA + H2O H3O+ + A-
Strong Acid
Weak Acid
HA + H2O + A-
H+ H2O
H3O+
· 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.
CAN YOU / HAVE YOU?
· Define electrolyte and explain the association with weak and strong.
· Explain the difference between weak and strong acid and base.
· Explain and compare dilute and concentrated solutions of acid or base.