EXPERIMENTS 291possible, using the flame spreader, and note if now any gas
issues from the delivery tube which is not absorbed by the
NaOH. Test the gas for its combustibility.Carbon dioxide is reduced by hot carbon to carbon monoxide
which is not an acidic oxide because it does not react with the base.
Carbon monoxide is combustible.
- Carbides, (a) The aluminum nitride made in Prepa-
ration 13 contains a considerable amount of carbide AI4C3.
Treat some of this product, or some commercial aluminum
carbide, with 6 N NaOH in a test tube with a delivery tube.
Collect some of the gas over water, which will dissolve all the
ammonia. Test the combustibility of this gas and find that
it burns with a nearly colorless flame.
(6) Drop a little calcium carbide, CaC 2 , into water in a test
tube; note that a gas is evolved and that this gas will burn
with an intensely luminous and very smoky flame.
Nearly all the metals form carbides which will hydrolyze more
or less readily. The hydrolysis products of aluminum carbide are
methane and aluminum hydroxide
A1 4 C 3 + 12H 2 O ->4A1(OH) 3 + 3CH 4from which it is concluded that in aluminum carbide the carbon
is acting as a simple negative radical with a valence of 4. Note
that the maximum negative valence of carbon is 4 as well as the
maximum positive valence (in CO2) and the arithmetical sum of
the maximum positive and negative valences is 8. No element
is known for which this sum exceeds 8, and, with a large number,
the value of 8 is equaled.
The hydrolysis product of calcium carbide is acetylene
CaC 2 + 2H 2 O -» Ca(OH) 2 + C 2 H 2
The weight of 22.4 liters of acetylene is 26 grams, which is equal
to the formula weight of C 2 H 2. It thus appears that there is
present in calcium carbide the complex carbon radical C 2 with a
negative valence of 2 for the whole radical.
- Silicon Dioxide and Silicic Acid, (a) Wet a little silicon
dioxide (very finely powdered quartz, or better the product
of Preparation 41), test with litmus, and note that litmus is not