Topic 7: Acids, bases and salts
7.1 THE CHARACTERISTIC PROPERTIES OF ACIDS AND BASES------------
ACIDS
● Aqueous solutions of acids contain H+ ions
○ When dissolved in water
● Formed from non-metal oxides
● Can neutralise a base, forming a salt and water
○ E.g HCl (aq) → H+ (aq) + Cl- (aq)
● pH < 7
Common acids:
● Sulphuric acid - H2SO4
● Hydrochloric - HCl
● Nitric - HNO₃-
SYLLABUS - Characteristics
Metals:
● Only metals above hydrogen in the reactivity
series will react with dilute acids
● Form a salt and hydrogen gas
● Acid + metal → salt + hydrogen
● The name of the salt is related to the name of the
acid used, as it depends on the anion within the acid
Bases:
● Metal oxides and metal hydroxides (alkalis) can
act as bases
● When they react with acid, a neutralisation
reaction occurs
● In all acid-base neutralisation reactions, salt
and water are produced
● Acid + base → salt + water
Carbonates:
● Acids will react with metal carbonates to form the
corresponding metal salt, carbon dioxide and
water
, ● Acid + metal carbonate → salt + carbon dioxide + water
SYLLABUS - Effect of acids
● Litmus is extracted from lichens
○ Not suitable for titrations, colour change is not
sharp and goes through a purple transition colour
in neutral solutions → difficult to determine
endpoint
● Synthetic indicators are organic compounds that are
sensitive to changes in acidity and appear different colours in acids and alkalis - Thymolphthalein and
methyl orange
○ Show endpoint in titrations as they have a very sharp change of colour when an acid has been
neutralised by alkali and vice-versa
BASES
● A base which is water-soluble is referred to as an alkali
● Aqueous solutions of bases contain OH- ions
○ When dissolved in water
○ The presence of the OH- ions is what makes the aqueous solution an alkali
● Formed from metal oxides
● Bases are usually oxides or hydroxides of metals
● Bases are oxides or hydroxides of metals
● Alkalis are soluble bases
● pH > 7
● Bases are substances which can neutralise an acid, forming a salt and water
● E.g NaOH (s) → Na+ (aq) + OH- (aq)
SYLLABUS - Characteristics
Acids:
● When bases react with an acid, a
neutralisation reaction occurs
● Acids and bases react together in a
neutralisation reaction and produce
a salt and water
● Acid + base → salt + water
Ammonium salts:
● Ammonium salts undergo decomposition when warmed with an alkali
● Ammonia is a weak base, but is very volatile + easily displaced from the salt by another alkali
● A salt, water and ammonia are produced
7.1 THE CHARACTERISTIC PROPERTIES OF ACIDS AND BASES------------
ACIDS
● Aqueous solutions of acids contain H+ ions
○ When dissolved in water
● Formed from non-metal oxides
● Can neutralise a base, forming a salt and water
○ E.g HCl (aq) → H+ (aq) + Cl- (aq)
● pH < 7
Common acids:
● Sulphuric acid - H2SO4
● Hydrochloric - HCl
● Nitric - HNO₃-
SYLLABUS - Characteristics
Metals:
● Only metals above hydrogen in the reactivity
series will react with dilute acids
● Form a salt and hydrogen gas
● Acid + metal → salt + hydrogen
● The name of the salt is related to the name of the
acid used, as it depends on the anion within the acid
Bases:
● Metal oxides and metal hydroxides (alkalis) can
act as bases
● When they react with acid, a neutralisation
reaction occurs
● In all acid-base neutralisation reactions, salt
and water are produced
● Acid + base → salt + water
Carbonates:
● Acids will react with metal carbonates to form the
corresponding metal salt, carbon dioxide and
water
, ● Acid + metal carbonate → salt + carbon dioxide + water
SYLLABUS - Effect of acids
● Litmus is extracted from lichens
○ Not suitable for titrations, colour change is not
sharp and goes through a purple transition colour
in neutral solutions → difficult to determine
endpoint
● Synthetic indicators are organic compounds that are
sensitive to changes in acidity and appear different colours in acids and alkalis - Thymolphthalein and
methyl orange
○ Show endpoint in titrations as they have a very sharp change of colour when an acid has been
neutralised by alkali and vice-versa
BASES
● A base which is water-soluble is referred to as an alkali
● Aqueous solutions of bases contain OH- ions
○ When dissolved in water
○ The presence of the OH- ions is what makes the aqueous solution an alkali
● Formed from metal oxides
● Bases are usually oxides or hydroxides of metals
● Bases are oxides or hydroxides of metals
● Alkalis are soluble bases
● pH > 7
● Bases are substances which can neutralise an acid, forming a salt and water
● E.g NaOH (s) → Na+ (aq) + OH- (aq)
SYLLABUS - Characteristics
Acids:
● When bases react with an acid, a
neutralisation reaction occurs
● Acids and bases react together in a
neutralisation reaction and produce
a salt and water
● Acid + base → salt + water
Ammonium salts:
● Ammonium salts undergo decomposition when warmed with an alkali
● Ammonia is a weak base, but is very volatile + easily displaced from the salt by another alkali
● A salt, water and ammonia are produced
