0620 Chemistry Topic 7 Notes - Acids, Bases, and Salts
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Course
Cambridge IGCSE Chemistry
Institution
Fourth Year / 10th Grade
These topic notes have been made in conjunction with the 0620 Cambridge IGCSE Chemistry syllabus, utilising diagrams and explanations from various study resources. They cover all the syllabus statements for Topic 7 of the syllabus - Acids, Bases, and Salts. The notes are written in concise bullet p...
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
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
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