202 ALKALI AND ALKALINE EARTH METALSSuggestion: Make use of the difference in solubility of barium
chloride and barium hydroxide.
Experiments
Very few of the chemical properties of the non-metals are dis-
played except in conjunction with the metals; in our study of the
non-metals in the preceding chapters, therefore, we already have
had revealed to us many of the chemical properties of the metals.
- Place a few small lumps of marble (calcium carbo-
nate) in a small porcelain crucible. Cover the crucible in
order to keep in the heat, and heat it strongly for 20 minutes
with a Bunsen flame. When the product has cooled, wet
each lump with a single drop or two of water and wait a few
minutes, if necessary, to observe the effect. The lumps
should grow very hot, and steam be driven off. Then wet
the product with somewhat more water, and test the reaction
of the moist mass towards litmus. The litmus is colored
strongly blue by the suspension.
It requires a bright red heat to decompose CaCO3 into CaO
and CO 2. The CaO is a strongly basic oxide and combines
strongly with water to form the base Ca(0H) 2 , as is evidenced by
the heat evolved. Ca(0H) 2 is sparingly soluble but enough dis-
solves to color litmus strongly blue.
- Place a few grams of magnesium carbonate in a 4-inch
porcelain dish and heat it rather moderately, testing to see if
carbon dioxide is being expelled. From time to time test the
residue for carbonate by removing a little from the dish,
thoroughly wetting it with about 5 cc. of hot water in a test
tube, adding acid, and watching for effervescence. Very
gentle heating suffices to change the magnesium carbonate
so that it no longer effervesces with dilute HC1.
In both calcium carbonate and magnesium carbonate, which
may be formulated CaO-CO 2 and MgO-CO 2 , we have the same
acid anhydride, CO 2. The tenacity with which the basic an-
hydrides CaO and MgO hold this acid anhydride is a measure of
their basic strength. Magnesium oxide is, therefore, less strongly
basic than calcium oxide.