206 ALKALI AND ALKALINE EARTH METALS
solubility of the hydroxide in grams per 100 grams of water at
25°; (6) the formula of the sulphate; (7) the solubility of the sul-
phate at 25°; (8) the formula of the carbonate; (9) the solubility
of the carbonate at 25°; (10) the formula of the chloride; (11) the
solubility of the chloride at 25°.
- Make a similar table of the elements of Group II, Family A,
including magnesium.
- Give the same information for ammonium. Discuss the
difference between ammonium and ammonia.
- Make a list of the percentage of ionization of the hydroxides
of the alkali metals, of ammonium, and of the alkaline earth
metals in 0.1 N solution if the substance is soluble to that extent.
Give figures for the hydroxyl-ion concentration in 0.1 N NH4OH
solution and in saturated solutions of Ca(0H) 2 and Mg(0H) 2.
Describe and discuss the results of Experiment 4 in the light of
these figures.
- An oxy-salt, such as CaC0 3 (= CaO-CO 2 ), can be broken
up by a sufficiently high heat into a basic oxide and an acid oxide —
for example, CaOC0 2 —> CaO + CO 2. The higher the tempera-
ture necessary to accomplish this, the greater is the chemical
affinity between the two oxides, that is, the more strongly basic
and acidic, respectively, are these two components; and therefore
in a series of salts, all containing the same acidic oxide — for
example, CaCO 3 , SrCO 3 , BaCO 3 — the greater the stability of the
salt, the stronger is the basic oxide. Compare the approximate
temperatures at which the alkaline earth carbonates are decom-
posed, and list the alkaline earth oxides in the order of their
basic strength.
The carbonates of the alkali metals are practically undecom-
posable by heat alone. Compare the basic strength of the alkali
metal oxides as a family with that of the alkaline earth oxides.
- More precise information as to the relative basic strength
may be given from the molal heats of formation in a series of
oxy-salts like the carbonates. In the thermochemical tables
sometimes the figure that we want is given, namely, the heat of
formation of the salt from the metal oxide and the non-metal oxide,
for example, MgO + CO 2 -• MgCO 3 + 28,850 calories. But
more often we will find only the heat of formation from the ele-
ments, for example, Mg + C + fO 2 —• MgCO 3 + 269,900 cal-
ories. We must then look up the heat of formation of mag-
