Everything Science Grade 10

18.4 CHAPTER 18. REACTIONS IN AQUEOUS SOLUTION

It is important to understand what happened in the previous demonstration. We will look

at what happens in each reaction, step by step.

Forreaction 1you have the following ions in your solution: Cu2+, Cl−, Na+and CO^23 −.

A precipitate will form if any combination of cations and anions can become a solid. The

following table summarises which combination will form solids (precipitates) in solution.

Salt Solubility

Nitrates All aresoluble

Potassium, sodium and ammonium salts All aresoluble

Chlorides, bromides and iodides All aresolubleexcept silver, lead(II) and mercury(II)

salts (e.g. silver chloride)

Sulphates All aresolubleexcept lead(II) sulphate, barium sul-

phate and calcium sulphate

Carbonates All areinsolubleexcept those of potassium, sodium

and ammonium

Compounds with fluorine Almost all aresolubleexcept those of magnesium, cal-

cium, strontium (II), barium (II) and lead (II)

Perchlorates and acetates All aresoluble

Chlorates All aresolubleexcept potassium chlorate

Metal hydroxides and oxides Most areinsoluble

Table 18.1: General rules for the solubility of salts

Tip

Salts of carbonates,
phosphates, oxalates,
chromates and sul-
phides are generally
insoluble.

If you look under carbonates in the table it states that all carbonates areinsolubleexcept

potassium sodium and ammonium. This means that Na 2 CO 3 will dissolve in water or

remain in solution, but CuCO 3 will form a precipitate. The precipitate that was observed

in the reaction must therefore be CuCO 3. The balanced chemical equation is:

2 Na+(aq)+CO 32 −(aq)+Cu2+(aq)+ 2Cl−(aq)→CuCO 3 (s)+ 2Na+(aq)+ 2Cl−(aq)

Note that sodium chloride does not precipitate and we write it as ions in the equation. For

reaction 2we have Cu2+, Cl−, Na+and SO^24 −in solution. Most chlorides and sulphates

are soluble according to the table. The balanced chemical equation is:

2 Na+(aq)+SO^24 −(aq)+Cu2+(aq)+2Cl−(aq)→ 2 Na+(aq)+SO^24 −(aq)+Cu2+(aq)+2Cl−(aq)

Both of these reactions are ion exchange reactions.

322 Chemistry: Chemical change