Chemistry, Third edition

IONIC EQUATIONS

Solubilities of ionic compounds

Table 6.2 shows the solubilities of common ionic compounds. If an ionic compound

is insoluble, then that substance will fall out of (or precipitatefrom) solution when

the appropriate ions are present. For example, if copper(II) sulfate solution is added

to sodium carbonate solution, Table 6.2 shows that the combination of

copper(II) and carbonate ions forms a precipitate of copper(II) carbonate:

Cu^2 (aq)CO 32 (aq)CuCO 3 (s)

copper carbonate

Where the compound is listed in Table 6.2 as slightly soluble, the precipitate may

appear only as a milkiness in the solution.

85

Zn

Zn

Zn

Zn

Cu2+ Cu2+

Cu2+ Cu2+

(b)

Cu Cu Cu Cu

Zn2+ Zn2+

Zinc rod

SO 4 2–

Zn

Zn

Zn

Zn

SO 4 2–

SO 4 2–

SO 4 2–

Cu2+

Cu2+

Cu2+

Cu2+

(a) Composition of the
starting mixture

Copper

SO 4 2–

Zn2+

SO 4 2–

SO 4 2–

SO 4 2–

Cu

Composition of the

mixture at the end

Cu Cu Cu

Zn2+

Zn2+

Zn2+

Zn2+ Zn2+

Fig. 6.1The reaction of copper(II)

sulfate solution with zinc metal.

Table 6.2The colours of common cations and the solubilities of common

salts. With three exceptions, all the cations are colourless in solution. All

the anions are colourless in solution.

Cation Cl,SO 42  CO 32  S^2  OH NO 3  CH 3 C0O

Br, I

Na, K, NH 4 

Mg^2  ● d ●

Ca^2  ●●d

Ba^2  ●●d

Al^3  –d●

Zn^2  ●● ●

Cu^2  (blue) ●● ●

Fe^2 (pale green) ●     ●

Fe^3 (yellow brown) – d ●

Pb^2  ●●●●●

Ag ●   ●●–

A blank indicates that the salt is soluble, ●salt is insoluble, salt is slightly soluble,

ddecomposes in water, – does not exist