94 THE THEORY OF IONIZATIONthrough transition shades to a clear yellow, the latter color being
reached before the neutral point is reached. The yellow color re-
mains the same in neutral solution and in the presence of hydroxyl
ions.
In five test tubes place respectively 10 cc. of liV HC1, 10 cc.
of liV HAc, 10 cc. of liV HAc, 10 cc. of pure water, 10 cc. of liV
NaOH, and to each add 2 drops of methyl orange solution. The
first tube shows the pink color imparted by strong acids, and the
fourth and fifth the yellow color. The second and third tubes
should, of course, show exactly the same color tone. Now drop
into the third tube about a gram and a half of crystallized sodium
acetate, NaC2H 3 O2-3H 2 O, and dissolve the salt by shaking. Now
compare the colors of the second and third tubes, still keeping
the other tubes for reference colors.
(6) The acid strength may be compared by the rapidity of the
reaction with calcium carbonate. In each of two small beakers
place 1 gram of powdered calcium carbonate and 10 cc. of water,
and stir until the powder is entirely wet. Have ready two solu-
tions as follows: one consists of 30 cc. of 1N acetic acid, the other
of 30 cc. of 1N acetic acid in which an equivalent amount, about
4 grams of sodium acetate, NaC2H 3 O2-3H 2 O, has been dissolved.
At the same instant add the two solutions to the respective
beakers containing calcium carbonate. The rapidity of efferves-
cence should be compared, also the time it takes for the solid to
dissolve entirely.
Notes and Problems
MEASUREMENT OF IONIZATION
Molal Lowering of the Freezing Point. The temperature at
which pure water is in equilibrium with ice is the standard fixed
point of thermometry and is designated as 0° on the centigrade
scale. This point, which is called the freezing point, is reproducible
to the greatest precision of thermometric measurements. This
point is reproducible, however, only when the water is pure.
Substances in solution in the water always lower the freezing point,
and not only that, the extent of the lowering of the freezing point
follows some very simple rules with a precision great enough to
make those rules apparent: For non-electrolytes, that is, sub-
stances whose solutions do not conduct electricity, the first rule