Titration
When the desired salt is soluble, and can be prepared by using an
aqueous acid and an aqueous alkali. eg. Sodium chloride from sodium
hydroxide and hydrochloric acid. Titration allows for exact
neutralization and hence you get a pure salt without contaimination
from acid or alkali.
Ionic Precipitation
When the salt is insoluble, and can be prepared by using two
aqueous solutions, that can either be salts, acids or alkalis. Eg.
lead(II) sulphate from sulphuric acid or sodium sulphate, and
lead(II) nitrate. Filter, the desired salt is the residue, the
filtrate solution consists of leftover ions – in this case,
HNO3 or NaNO3. Because one salt obtained is
aqueous and the other (the desired salt) is solid, you can use
filtration to easily separate the salts and prevent contamination
of your desired salt (eg. PbSO4) by either the other salt (eg.
NaNO3), or any acid (eg. H2SO4 or
HNO3) if such is used or produced.
Acid with excess insoluble base/carbonate.
When the salt is soluble, and can be prepared by using an aqueous
acid and an insoluble base/carbonate. Eg. copper(II) sulphate from
sulphuric acid and copper(II) carbonate or copper(II) oxide.
Basically, neutralization occurs, same as titration. Reason for
difference between this method and titration is, since the base
copper(II) oxide is not soluble and you cannot obtain aqueous
copper(II) hydroxide, you use excess of the solid (either the oxide
or the carbonate) with limited acid, so that you can easily
separate (using filtration) the desired pure aqueous salt, and the
excess solid. Hence, like titration, this method has its own way of
preventing contaimination of the salt (by using
excess solid here).
“These are the salts which I am not able to decide their
solubility”.
Google for a list of salts and their solubilities.
“Lastly, are silver nitrate and magnesium sulphate soluble can
can be prepared by the acid with excess insouble base/carbonate
method?”
If these salts were insoluble, you CANNOT use acid with base/carbonate method. Why
not? This is a common exam question. Think about it. (hint : the
yield will be low; the reaction will cease very quickly).
“Oh, i forgot to ask, is titration ONLY
meant for getting back sodium, potassium and ammonium salts?”
Never be a dogmatic student who memorizes notes
without understanding. Do not merely memorize
“titration ONLY meant for getting back
sodium, potassium and ammonium salts”, but UNDERSTAND WHY (why this is given as a useful
guideline, NOT a rule to be
followed unthinkingly merely for the sake of obeying rules!).