8/18/2019 Methods of Preparing Salts
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Dr. Mohammad Salleh Abid Page 1
SALTS – ASSUME SALTS ARE SOLUBLE AND LEARN THE
EXCEPTIONS
The common salts are chlorides, sulphates and nitrates.
ALL sodium and potassium salts are soluble.
ALL ammonium salts are soluble.
ALL nitrates are soluble.
ALL chlorides/halides are soluble except sil ver and l
ead (PbCl2 dissolves in hot water)
ALL sulphates are soluble except barium, l ead and
calcium (although calcium sulphate is very sparingly
soluble – rather borderline!)
8/18/2019 Methods of Preparing Salts
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Dr. Mohammad Salleh Abid Page 2
Methods of Preparing Salts
Soluble salts
Salts from soluble metals and bases
(sodium, potassium and ammonium)
Titrat ion method u sing an
indicator
Measure a known volume of acid into aflask or beaker.
Add a suitable indicator.
Add alkali a little at a time from aburette until the
indicator justchanges colour.
Note the volume of alkali used.
Mix the known volumes of acid and alkaliBUT with NO
indicator (indicator would make the salt impure)
Salts from insoluble metals and bases
(magnesium, copper, zinc)
Measure out some of the appropriate acid intoa beaker.
Add the solid base (metal oxide, metalhydroxide or metal
carbonate) a little at a timeuntil no more will dissolve. (This
tells you
that all the acid has been neutralised)Warm if necessary to
speed up the reaction
Filter the mixture to remove the unreactedbase.Collect the
filtrate (solution of the desired salt)
HYDRATED ---Concentrate the solution by heating over a Bunsen,
tripod and gauze or overa hot water bath to evaporate some water
and make the solution saturated.
Allow it to cool and crystallise slowly at room
temperature –forms Crystal with water ofcrystallisation
ANHYDROUS --Evaporate all the water to get dry, anhydrous
powder instead of
crystals
Insoluble salts
e.g. Barium Sulphate
Take samples of solutions of twocompounds each containing one
ofthe ‘halves’ (ions) in the required saltandMix together (two
soluble salts)
e.g. Barium nitrate – Ba2+ andpotassium
sulphate – SO4
2-
Filter the mixture to separate the solidprecipitate of the
required salt from thesolution. The precipitate is the residue
in
the filter paper
Wash the solid with distilled water to
remove any traces of the other substanceleft in
solution.(Dry )Spread the filter paper out to allow the
solid to dry, either in the open lab. or in a
