Additional Science
C2- Chemistry
Analysing substances, making
salts, acids and bases
Instrumental methods of
analysing substances such as
elements and compounds are;
accurate, rapid and sensitive
Paper chromatography can be
used to detect additives in
food.
Artificial colours can be
identified.
Lid to prevent
evaporation of
the solvent.
Unknown sample.
Solvent; dissolves the
colours and is absorbed
through the paper.
Known samples.
Pencil line; starting
point, pencil does
not dissolve in the
solvent.
The colour dots from the unknown sample which match the known
samples can be identified as to whether the additive is safe or not.
Gas chromatography linked to mass spectroscopy (GC-MS) is an
example of an instrumental method:
Gas chromatography separates mixtures of compounds, it uses a
column packed with solid.
The substance to be analysed is carried
through the column using a gas
The time taken for a substance to travel through the column can be
used to help identify the substance
The number of peaks corresponds to the number of compounds
present
The position of the peak is the ‘retention time’, in other words how
long they have spent in the column
The gas chromatography column can be linked to a mass spectrometer
which can identify substances quickly and accurately and in very small
quantities.
The mass spectrometer can give the relative molecular mass of the
substances (you look at the molecular ion peak on a graph)
H+(aq) + OH-(aq)  H2O
(l)
State symbols are shown after substances in reactions
(s)= solid
(l)= liquid
(aq) = aqueous (dissolved in water)
(g) = gas
Soluble salts can be made by reacting acids with:
1. metals – not all metals are suitable; some are
too reactive and others are not reactive enough
(MASH)
2. insoluble bases – the base is added to the acid
until no more will react and the excess solid is
filtered off (copper sulphate)
3. alkalis – an indicator can be used to show when
the acid and alkali have completely reacted to
produce a salt solution. (neutralisation)
Soluble salts can be made by reacting acids with:
1. metals – not all metals are suitable; some are
too reactive and others are not reactive enough
(MASH)
Metal + Acid  Salt + Hydrogen
• Hydrochloric acid produces metal chlorides
e.g. Sodium chloride
• Sulphuric acid produces metal sulphates
e.g. Sodium Sulphate
• Nitric acid produces metal nitrates
e.g. sodium nitrate
Soluble salts can be made by reacting acids with:
2. insoluble bases – the base is added to the acid
until no more will react and the excess solid is
filtered off (copper sulphate)
Soluble salts can be made by reacting acids with:
3. alkalis – an indicator can be used to show when
the acid and alkali have completely reacted to
produce a salt solution. (neutralisation)
Acid + Alkali  Salt + Water
Hydrochloric + Sodium
acid
hydroxide
Sodium
Chloride
H+(aq) + OH-(aq)  H2O
+ Water
(l)
Salts solutions (aq) can be crystallised to produce
solid salts (s)
Insoluble salts can be made by reacting two soluble salts
together. This is called a precipitation reaction.
Soluble except when with silver,
mercury or lead.
All soluble
Soluble except when with silver,
lead, mercury, barium, strontium
and calcium.
Insoluble salts can be made by reacting two soluble salts
together. This is called a precipitation reaction.
All insoluble except for NH4+,
barium and those of group 1
elements
All insoluble except for calcium,
barium and group 1
All insoluble except when with
NH4+ and group 1 elements
An example precipitation reaction
Silver + Sodium
nitrate
chloride
Sodium
nitrate
+
Silver
chloride
AgNO3(aq) + NaCl(aq) → NaNO3(aq) +AgCl(s)
Precipitation reactions are used to remove unwanted
ions from solutions, for example to treat drinking water
or treating effluent
Metal oxides and metal hydroxides are bases e.g.
sodium hydroxide, copper oxide.
If the hydroxides are soluble they are called alkalis
Hydrochloric + Sodium
acid
hydroxide
Sodium
Chloride
+ Water
The name of the salt produced when an acid and alkali
react depends on the acid used and the metal in the base
Ammonia (NH3) dissolves in water to form an alkali
solution, NH3 (aq).
It is used to produce ammonium salts
These salts are used as fertilisers
The presence of H+ ions makes solutions acidic.
The presence of OH- ions make solutions alkali.
1 2 3 4 5 6 7 8 9 10 11 12 13 14
Strong acid
Neutral
Weak acid
Strong alkali
Weak alkali
More acid
More alkali
More H+ ions
More OH- ions
In neutralisation reactions, hydrogen ions react with
hydroxide ions to produce water.
Acid + Alkali  Salt + Water
nitric + potassium
acid
hydroxide
potassium
nitrate
H+(aq) + OH-(aq)  H2O
+ Water
(l)