Synthetic Inorganic Chemistry

288 ELEMENTS OF GROUP IV

nearly if not quite coincide with the light mark). Shake

the tube vigorously for 60 seconds, then place the mouth

of the tube under water in the pan, remove the thumb, and

mark the level to which the water rises, calling this mark 2.

Now measure with a graduate, first, the volume between the

closed end of the tube and mark 1, thus giving the volume

of carbon dioxide taken; second, the volume between marks

1 and 2, thus giving the volume of carbon dioxide, measured

under atmospheric pressure, dissolved by the water; third,

the volume between mark 1 and the open end of the tube,

thus giving the volume of water in which the carbon dioxide

was dissolved. Take the temperature of the water in the

pan. The undissolved gas was under a pressure less than

atmospheric just before the thumb was removed from the

end of the tube. Calculate this pressure according to Boyle's

law from the volume. Then calculate the volume of carbon

dioxide that would be dissolved at the temperature of the

experiment in 1 volume of water if the gas were at atmos-

pheric pressure, applying Henry's law that the quantity of

a gas dissolved in a liquid is proportional to the pressure.

At 15° 1 volume of water will dissolve 1 volume of carbon
dioxide under 1 atmosphere pressure.

(c) Take a third tube of the gas, introduce 5 cc. of IN

NaOH, and shake as in (6). Note that except for a small

bubble, which is doubtless air introduced when the NaOH was

poured in, the gas is entirely dissolved by the solution.

The carbonic acid, which in (6) comes to equilibrium with the
carbon dioxide in the gas phase, is in this experiment neutralized
by the base,

H 2 CO 3 + 2NaOH -»• Na 2 CO 3 + 2H 2 O

and since 5 cc. of 1N NaOH reacts, according to the equation, with
carbonic acid equivalent to 56 cc. of carbon dioxide, all the gas
is dissolved.

(d) Repeat (c) using 5 cc. of liV Na 2 CO 3 instead of

NaOH. Note that the gas is nearly if not all dissolved. If

the experiment is repeated and the shaking is continued for

a longer time the gas is entirely dissolved.