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Chemistry IGCSE
Chemistry, 8: Acids, bases, and salts
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An
aqueous
solution is formed when a substance
dissolves
in water
It can be
acidic
,
alkaline
, or neutral
A
neutral
solution is neither acidic or
alkaline
Red litmus papers show
acidic
solutions
Blue
litmus paper shows
alkaline
solution
Phenolphthalein
indicator is
colourless
in acid, but pink in alkaline solutions
Methyl
orange is
pink
in acid, but yellow in alkaline solution.
Acids are
substances
that contains
replaceable hydrogen atoms
They can be replaced by
metal
atoms to form
salts
Acids
have a pH of
0-6
What are some common acids?
Hydrochloric
acid,
HCl
Nitric
acid,
HNO3
Sulfuric
acid,
H2SO4
Phosphorous
acid,
H3PO4
Acidic
properties are only seen when
water
is present
In water,
acids
form
hydrogen
ions
H+
ions create this
acidic
properties
Acids
are
proton
donors
E.g.
HCl
-> H+ +
Cl-
What happens when an acid and metal reacts?
Makes
salt
and
hydrogen
gas
What happens when an acid and carbonate reacts?
Makes salt
,
carbon dioxide
, and water
What happens when an
acid
and base
reacts
?
Makes salt and water
Bases are
oxides
and
hydroxides
of metals
Alkalis
form when oxides or hydroxides of a metal
dissolves
in water
E.g. sodium + oxygen ->
sodium oxide
sodium oxide +
water
->
sodium hydroxide
Sodium oxide is a base because it is the
oxide
of
sodium
It reacts with
water
to make
alkali sodium hydroxide
What happens when a base and acid reacts?
Forms
salt
and
water
What happens when a base and ammonium compound reacts?
Forms
ammonia gas
Alkalis only show
alkaline
properties in presence of
water
In
water
, alkalis form
OH- ions
These
OH-
ions reacts with H+ ions from acid to make
water
Alkalis are
proton acceptors
If soil is too
acidic
, it can be neutralised with
quicklime
Quicklime
is made from
limestone
It is heated in
lime
kilns at
1200°C
to make calcium oxide
When it is added to water, it makes calcium hydroxide, an alkali that
neutralizes
the
soil
Oxides
of elements are made by
heating
it in air or oxygen
Basic oxides that
dissolves
in water are
alkalis
Oxides that do not dissolve in water can be identified using
pH
Or tested to react with:
HCl
, a
basic oxide
NaOH
,
acidic oxide
If they do not react with either they are
neutral oxides
Most metals are
basic oxides
Basic oxides
react with
acids
Acid + base ->
salt
+
water
Most
non-metal oxides
are
acidic
Acidic oxides react
with bases (neutralisee) and dissolves in
water
to form acid
Metal oxides react
with acids to make salt +
water
Non-metal oxides
react with base to make salt +
water
Amphoteric
oxides are oxides of
less reactive
metals
They behave as both
acid
and
basic
oxides
Neutral
oxides
do not react with acids or
bases
Acids contain
replaceable hydrogen
atoms which is replaced by
metal
to form a salt
What are common acids and salts?
HCl
,
Cl-
HNO3
,
NO3-
H2SO4
,
SO4^2-
H3PO4
,
PO4^3-
Salts are
ionic compounds
which are found in the form of
crystals
Salts that don’t contain
water
are
anhydrous
All common sodium,
potassium
, and ammonium salts are
soluble
All nitrates are
soluble
Common chlorides,
bromides
, and
iodides
are soluble
Excluding silver chloride,
silver bromide
, and
silver iodide
Common sulfates
are
soluble
Except barium,
lead
, and
calcium
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