Properties of Acids and Bases
Topic 8.2
But first, a review!
Acid
Arrhenius Definition
Base
An acid is any chemical
compound which when dissolved
A base is an aqueous substance
in water gives a solution with a
that can accept hydrogen ions.
hydrogen ion activity greater
than in pure water.
An acid is an substance which
donates a proton.
Less than 7.0
Blue litmus paper turns red
Remains colorless
A base is any substance which
accepts a proton.
Greater than 7.0
red litmus paper turns blue
Makes the solution pink
Dissociation (in water)
Acids free hydrogen ions (H+)
when mixed with water.
Bases free hydroxide ions (OH-)
when mixed with water.
Chemical Formula
An acid has a chemical formula
A base has a chemical formula
with H at the beginning of it. For
with OH at the end of it. For
example, HCl (Hydrochloric Acid).
example, NaOH (Sodium
There is one exception to his rule,
Hydroxide).
CH3COOH = Acetic Acid (vinegar).
Bronstead Lowry Definition
pH value
Litmus paper
Phenolphthalein
Practice problems
Identify the acid, base, conjugate acid,
conjugate base, and conjugate acid-base pairs:
HC2H3O2(aq) + H2O(l)  C2H3O2–(aq) + H3O+(aq)
acid
base
conjugate base conjugate acid
conjugate acid-base pairs
OH –(aq) + HCO3–(aq)  CO32–(aq) + H2O(l)
base
acid
conjugate base conjugate acid
conjugate acid-base pairs
(a) HF(aq) + SO32–(aq)  F–(aq) + HSO3–(aq)
acid
base
conjugate base conjugate acid
(b)
conjugate acid-base pairs
CO32–(aq) + HC2H3O2(aq)  C2H3O2–(aq) + HCO3–(aq)
base
acid
conjugate base conjugate acid
(c)
conjugate acid-base pairs
H3PO4(aq) + OCl –(aq)  H2PO4–(aq) + HOCl(aq)
acid
base
conjugate base conjugate acid
conjugate acid-base pairs
8a) HCO3–(aq) + S2–(aq)  HS–(aq) + CO32–(aq)
acid
base conjugate acid conjugate base
conjugate acid-base pairs
8b) H2CO3(aq) + OH –(aq)  HCO3–(aq) + H2O(l)
acid
base conjugate base conjugate acid
conjugate acid-base pairs
11a) H3O+(aq) + HSO3–(aq)  H2O(l) + H2SO3(aq)
acid
base
conjugate base conjugate acid
conjugate acid-base pairs
11b) OH –(aq) + HSO3–(aq)  H2O(l) + SO32–(aq)
base
acid conjugate acid conjugate base
conjugate acid-base pairs
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Properties of (some) Acids
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taste sour
cool to use in movies
corrode metals (produce H2 gas)
react with bases to form a “salt” (ionic compounds that
can result from the neutralization reaction of an acid
and a base) and water
• pH is less than 7
• turns blue litmus paper to red
• strong acids are strong electrolytes, weak acids are
weak electrolytes
Properties of (some) Bases
• produce OH- ions in solution (Arrhenius definition)
• taste bitter
•
•
•
•
•
•
feel soapy, slippery
dissolve oil and grease
react with acids to form a salt and H2O
pH is greater than 7
turns red litmus paper to blue
strong bases are good electrolytes, weak bases
weak electrolytes
Bases in Solution
• a soluble base is called an alkali
– when added to water release an OH- ion
• base(aq) = alkali
– K2O(s) + H2O(l)  2K+(aq) + 2OH-(aq)
– NH3(aq) + H2O(l) ⇌ NH4+(aq) + OH-(aq)
– CO32-(aq) + H2O(l) ⇌ HCO3-(aq) + OH-(aq)
– HCO3-(aq) ⇌ CO2(g) + OH-(aq)
The 5 Reactions of Acids
“swap the
hydrogen for
the metal”
Salt +
Water
(NH4)Salt
Water
METAL OXIDE
(base)
BASES
(without OH)
Salt +
Water
(base)
METAL
CARBONATE or HYDROGEN
CARBONATE
(base)
ACIDS
METAL
HYDROXIDE
Salt +
Water
+ CO2
METAL
(if more reactive than
hydrogen)
Salt +
H2
1. Acids reaction with metals
• most dilute acids react with metals above
hydrogen in the reactivity series (Topic 9) to
produce H2 gas and a solution of a salt
– in general:
• reactive metal + acid  “salt” + hydrogen
» Mg(s) + 2HCl(aq)  MgCl2(aq) + H2(g)
» Mg(s) + 2HNO3(aq)  Mg(NO3)2(aq) + H2(g)
» Mg(s) + H2SO4(aq)  MgSO4(aq) + H2(g)
» Mg(s) + 2CH3COOH(aq)  (CH3COO)2Mg(aq) + H2(g)
Reactivity series (Topic 9)
2. Acid reaction with metal hydroxides
• acids react to give salt and water when a
metal hydroxide(OH) or aqueous ammonia is
added
• in general:
– metal hydroxide + acid  “salt” + water
• NaOH(aq) + HNO3(aq)  NaNO3(aq) + H2O(l)
• KOH(aq) + H2SO4(aq)  K2SO4(aq) + H2O(l)
3. Acid reaction with metal carbonates or
hydrogen carbonates
• acids react to give CO2(g) when a metal
carbonate or metal hydrogen carbonate is added
• in general
– (metal)CO3 + acid  salt + water + carbon dioxide
• CaCO3(s) + 2HCl(aq)  CaCl2(aq) + H2O(l) + CO2(g)
– (metal)HCO3 + acid  salt + water + carbon dioxide
• NaHCO3(s) + HCl  NaCl(aq) + H2O(l) + CO2(g)
4. Acid Reaction with metal oxides
• acids react to give salt and water when a
metal oxide is added:
• in general:
– metal oxide + acid  “salt” + water
• CuO(s) + H2SO4(aq)  CuSO4(aq) + H2O(l)
• CuO(s) + 2HNO3(aq)  Cu(NO3)2(aq) + H2O
• CuO(s) + 2HCl(aq)  CuCl2(aq) + H2O(l)
• CuO(s) + 2CH3COOH(aq)  Cu(CH3COO)2(aq) +
H2O(l)
5. Acid reactions with bases (even
ones without an OH)
• a base is a substance that reacts with an acid to form
water and a salt only, this is known as neutralization
– most have an OH, however some do not
• in general:
– base + acid  salt + water
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•
•
•
•
NaOH(aq) + HNO3(aq)  NaNO3(aq) + H2O(l)
NH3(aq) + HNO3(aq)  NH4NO3(aq) (water is “assumed”)
NH3(aq) + H+(aq)  NH4+(aq) (water is “assumed”)
H3PO4(aq) + 3NaHCO3(s)  Na3PO4(aq) + 3H2O(l) + 3CO2(g)
CaCO3(s) + 2HCl(aq)  CaCl2(aq) + H2O(l) + CO2(g)
Salt +
Water
(NH4)Salt
Water
METAL OXIDE
(base)
BASES
(without OH)
Salt +
Water
(base)
METAL
CARBONATE or HYDROGEN
CARBONATE
(base)
ACIDS
METAL
HYDROXIDE
Salt +
Water
+ CO2
METAL
(if more reactive than
hydrogen)
Salt +
H2
Acids and bases effects on indicators
• indicators
– substances that change color in an acid or base
(concentration of hydrogen ions changes)
Color changes for different indicators
are on page 22 of the IB Data booklet