ACIDS
ACIDS
An acid → H+ in water
Some strong acids are
HCl
hydrochloric
HNO3
nitric
perchloric
HClO4
H2SO4
sulfuric
HCl(aq) → H+(aq) + Cl-(aq)
HNO3
Screen 5.8 on the CD-ROM.
Just as with strong electrolytes, strong acids ionize
(dissociate) very well in H2O.
May 5, 2006
May 5, 2006
Acids in water
Weak Acids
WEAK ACIDS are also weak electrolytes
acetic acid
• CH3CO2H
carbonic acid
• H2CO3
phosphoric acid
• H3PO4
• HF
hydrofluoric acid
HCl
CD-ROM screen 5.8
Cl-
+
H 2O
hydronium
ion
+
H 3O+
Acetic acid
May 5, 2006
May 5, 2006
Page 1
CD-ROM screen 5.8
1
Nonmetal oxides can form acids with water
Acid naming conventions
CO2(aq) + H2O(liq) →
H2CO3(aq)
SO3(aq) + H2O(liq) →
H2SO4(aq)
2 NO2(aq) + H2O(liq) →
HNO2(aq) + HNO3(aq)
For simple acids, with anion names ending in -ide, the
acid starts with hydro- and ends in -ic.
For oxoacids, with an anion containing oxygen and a
central, different atom, the anion naming convention
extends to the acid naming convention:
»
»
»
»
These are produced during the
burning of fossil fuels such as
coal and oil, and are a major
source of acid rain.
-ate anion makes -ic acid
-ite anion makes -ous acid
per- -ate anion makes per- -ic acid
hypo- -ite anion makes hypo- -ous acid
Note that sulfur and phosphorus are slight exceptions:
sulfate anion goes to sulfuric acid and sulfide anion
goes to hydrosulfuric acid.
May 5, 2006
May 5, 2006
Acid naming conventions
compound
HCl
H 2S
HCN
H3PO4
H2SO4
HClO4
HClO3
HClO2
HClO
acid
hydrochloric acid
hydrosulfuric acid
hydrocyanic acid
phosphoric acid
sulfuric acid
perchloric acid
chloric acid
chlorous acid
hypochlorous acid
BASES
Base → OH- in water
anion
chloride
sulfide
cyanide
phosphate
sulfate
perchlorate
chlorate
chlorite
hypochlorite
NaOH(aq) → Na+(aq) + OH-(aq)
NaOH is a
strong base,
that is, it
completely
ionizes in water.
May 5, 2006
May 5, 2006
Page 2
Screen 5.9 on the CD-ROM
2
Ammonia, NH3,
a weak base
BASES
Metal oxides are bases
in the presence of
water
NH3(aq) + H2O(liq)
→ NH4+(aq) + OH-(aq)
CaO(s) + H2O(liq)
→ Ca(OH)2(aq)
Screen 5.9 on the CD-ROM
May 5, 2006
May 5, 2006
CaO in water. pH
indicator shows that the
solution is basic.
Mg(s) + 2 H+(aq) + 2 Cl-(aq) →
H2(g) + Mg2+(aq) + 2 Cl-(aq)
Net Ionic
Equations
The two Cl- ions are SPECTATOR
IONS — they do not participate in the
reaction. The net ionic equation (NIE)
does not include them:
NIEs involve only the ions
that directly participate in a
reaction. Non-participants
Screen 5.11 on the CD-ROM are called spectator ions.
Mg(s) + 2 H+(aq) → H2(g) + Mg2+(aq)
Mg(s) + 2 HCl(aq) → H2(g) + MgCl2(aq)
The presence of spectator ions can be determined in
two ways:
• the same ion appears with the same stoichiometry
on both sides of the equation
• replacing the spectator with a different spectator ion
May 5, 2006not alter the reaction (i.e. Cl- → NO -)
does
3
We really should write
Mg(s) + 2 H+(aq) + 2 Cl-(aq) →
H2(g) + Mg2+(aq) + 2 Cl-(aq)
May 5, 2006
Page 3
3
Precipitation reactions follow balanced NIEs:
Acid-base reactions follow balanced NIEs
Add lead nitrate to sodium sulfide:
Pb(NO3)2 + Na2S → ?
A strong acid plus a strong base:
HNO3(aq) + KOH(aq) → ?
The lead nitrate forms Pb2+(aq) and NO3-(aq) and
the sodium sulfide forms Na+(aq) and S2-(aq).
The nitric acid and potassium hydroxide both
readily ionize to form H+(aq), NO3-(aq), K+(aq)
and OH-(aq). Neither the nitrate nor the potassium
ions participate; they are spectators.
Neither NO3-(aq) nor Na+(aq) participate in
forming the precipitate, so they are the spectators.
The NIE is
NIE:
Pb2+(aq) + S2-(aq) → PbS(s)
May 5, 2006
May 5, 2006
Page 4
H+(aq) + OH-(aq) → H2O(l)
4