Chemistry salt preparation

Hmyatthazin SG

My school Chemistry teacher said that insoluble salt can as well be prepared by reacting acid with soluble salt. For eg, hydrochloric acid+silver nitrate------>sliver chloride+nitric acid. Is there such reaction? Because I have only heard of percipitation of two soluble salts to get insoluble salt.

UltimaOnline SG

Insoluble salts are best prepared (ie. for maximum yield) by mixing two suitable aqueous solutions that when combined, contains the desired cations and anions of the insoluble salt.

So it doesn't matter whether one of the solutions happens to be an acid or a salt, as long as the desired ion is present.

In other words, when mixing

(i) aqueous hydrochloric acid + silver nitrate solution,

(ii) sodium chloride solution + silver nitrate solution,

The ionic equation is exactly the same :

Cl-(aq) + Ag+(aq) ---> AgCl(s)

It's only the spectator ions which are different. The spectator ions from (i) are H+(aq) and NO3-(aq), hence the filtrate would be nitric(V) acid. In (ii), the spectator ions are Na+(aq) and NO3-(aq), hence the filtrate would be sodium nitrate solution.

But you don't really care about the spectator ions, coz as far as you're concerned, you really only want the insoluble silver chloride precipitate salt.

Hmyatthazin SG

Does it mean that all soluble salts and acids can react to from a different insoluble salts? I thought that only basic salts will react with acids…

UltimaOnline SG

Does it mean that all soluble salts and acids can react to from a different insoluble salts? I thought that only basic salts will react with acids…

As long as any cation from the 1st aqueous solution (you don't care whether it is an acid or salt solution) can combine with any anion from the 2nd aqueous solution (you don't care whether it is an acid or salt solution) to precipitate out an insoluble ionic compound (for this you will have to memorize the list of solubilities of the various ionic compounds), then that's what will happen - we label such 'reactions' as "ionic precipitation reactions".

The reason why you may be confused, is that you're confusing Bronsted-Lowry acid-base (ie. proton transfer) reaction with ionic precipitation reaction. The former occurs only between an Bronsted-Lowry acid (ie. proton donor) and a Bronsted-Lowry base (ie. proton acceptor). The latter occurs between any cation and anion for which the ionic compound is insoluble (ie. for sparingly soluble ionic compounds, the solid precipitate forms when ionic product > solubility product).

Note :

The term 'protons' as used in acid-base chemistry refer to H+ ions. For protium hydrogen (as opposed to deuterium hydrogen and tritium hydrogen), a H+ cation is simply a proton.

Edited :

(Stating the obvious, for any posts, eg. mine)

If you're 'O' levels and unfamiliar with some of these terms, you have the choice of checking them out (Wikipedia is the best thing that the Internet Age has brought forth) for a deeper understanding of Chemistry, or you can simply ignore these terms. It's fine either way, you just have to choose for yourself.