8.1 EXPLAINING THE PROPERTIES
OF ACIDS & BASES
SCH4U - Chemistry, Gr. 12, University Prep
Mr. Dvorsky
Common Properties of Acids & Bases
Property
Acid
Base
Taste
Sour
Bitter
Texture of Solution
No characteristic texture
Slippery
Aqueous Property of Oxides
Non-metal oxides form acidic solutions:
CO2(g) + H2O(l)  H2CO3(aq)
Metal oxides form basic solutions:
CaO(g) + H2O(l)  Ca(OH)2(aq)
Reaction with Phenolphthalein
Colourless
Pink
Reaction with litmus paper
Blue litmus  Red
Red litmus  Blue
Reaction with Metals
Acids react with metals above H in the
activity series to displace H2(g)
Bases react with certain metals (i.e.
Al) to form H2(g)
Reaction with CO32-
Form CO2(g)
No reaction
Reaction with NH4Cl
No reaction
Form NH3
Reaction with Fatty Acids
No reaction
React to form soap
(saponification reaction)
Neutralization Reactions
Acid + Base  Water + Salt
Arrhenius Theory of Acids & Bases
(Arrhenius, 1887)


Acids & bases are defined in terms of their structure and
the ions produced when they dissolve in water.
Explains acid-base reactions and neutralization.
 ACID:
 HCl
 BASE:
dissociates in water to form H+(aq)
(hydrochloric acid), H2SO4 (sulphuric acid)
dissociates in water to form OH-(aq)
 NaOH

(sodium hydroxide), KOH (potassium hydroxide)
LIMITATIONS:
 hydrogen
H (aq)  H 2O(l )  H 3O(aq)
ion combines with water to form hydronium ion
 does not explain some bases (i.e. ammonia, salt solutions)
 does not explain acid-base reactions without water (i.e. gas)
Brønsted-Lowry Theory
(Johannes Brønsted & Thomas Lowry, 1923)

Recognizes an acid-base reaction as chemical
equilibrium, have a forward and reverse reaction
involving the transfer of a proton
proton = nucleus of a hydrogen atom (H+ ion)
 ACID:
substance from which a proton can be removed
 “proton-donor”
 BASE:
substance that can accept a proton
 “proton-acceptor”

( aq)
HCl( aq)  H 2O(l )  H3O
acid
base
conjugate
acid

( aq)
 Cl
conjugate
base
Conjugate Acid-Base Pairs
NH 3( aq)  H 2O(l )  NH
base

acid

4 ( aq )
 OH
conjugate
acid

( aq )
conjugate
base
dissociation is an equilibrium reaction because it
proceeds in both directions
donates a proton in forward rxn  acid
 OH- accepts a proton in reverse rxn  conjugate base
 H2O

If a substance acts as a proton donor
and a proton accepter,
it is termed “amphoteric” (i.e. water)
Strong Acids

Completely dissociates in water
(equilibrium favours products, lies to the right)

Binary acids
[HX(aq) where X = Cl, Br, I (not F)]

Factors:



Oxoacids (contain oxygen atoms)
where the # [O] > # H (by 2 or more)

Factors:


Number of oxygen atoms
Monoprotic


Across period: electronegativity
Down a group: bond strength
only have single H atom that dissociates
Polyprotic


have more than 1 H atom that dissociates
Strength decreases as number of hydrogen
atoms that have dissociated increases
HCl( aq)  H 2O(l )  H3O(aq)  Cl(aq)
Strong Bases

Completely dissociates in water
(equilibrium favours products, lies to the right)
 Oxides
& Hydroxides of alkali metals (Group 1) and of
of alkali earth metals (Group 2) below beryllium
[e.g. NaOH sodium hydroxide, MgO magnesium oxide]

Factors:

Metals with low electronegativity form ionic bonds with oxygen
 easily break bond with oxygen which reacts with water to form
hydroxide ions
Na2O( aq)  H 2O(l )  2 Na(aq)  2OH (aq)
Na2O( aq)  2 Na(aq)  O(2aq )
O(2aq )  H 2O(l )  2OH (aq)
Calculations that involve
strong acids & bases

Strong acids/bases (and strong electrolytes)
completely dissociates into ions in water
 [H3O]+(aq)
is equal to the [strong acid]
 [OH]-(aq) is equal to the [strong base]

You cannot determine the concentrations of ions of
weak acids/bases/electrolytes this way because
they do not completely dissociate in solution (more
next class)