ACIDS AND BASES. HA + H 2 O base acid H 3 O + + A - Con. baseCon. acid B + H 2 O base acid BH + + OH...
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Transcript of ACIDS AND BASES. HA + H 2 O base acid H 3 O + + A - Con. baseCon. acid B + H 2 O base acid BH + + OH...
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.