Synthetic Inorganic Chemistry

MEASUKEMENT OF IONIZATION 95

is that, with the same substance, the extent of the freezing point
depression is proportional to the quantity of substance dissolved
in a given weight of water. The second rule is that, for different
substances, equimolal amounts produce the same freezing point
lowering with the same amount of water. A statement com-
bining these two rules is as follows: The lowering of the freezing
point is proportional to the number of moles of dissolved sub-
stance in a given amount of water. The proportionality factor is
given by the moled lowering of the freezing point, which is 1.86°C.
and is the effect produced by one mole of dissolved substance in
1,000 grams of water. This rule holds only when the solid sepa-
rating from the solution is pure ice, but this is almost invariably
the case when the solution is fairly dilute.
It should be clear that the above statements show a method
of determining the molecular weight of a substance dissolved in
water provided that the substance is a non-electrolyte.
The same regularities hold for solutions in solvents other
than water except that there is a different proportionality factor;
i.e., the molal lowering of the freezing point is different for each
different solvent.
The following set of problems will allow the student to find
whether he has grasped the significance of the statements in the
foregoing paragraphs. For the present we will consider the be-
havior of electrolytes as irregular. In a later section we will try
to discover any regularity that may appear in the " irregularities "
and see if that too can be reduced to any significant rule.

1. At what temperature will a solution freeze that is made
   by dissolving 1 gram of sugar, C12H22O11, in 10 grams of
   water?


2. — one mole of urea, CO(NH 2 )2, in 10 liters of water?


3. How many grams of methyl alcohol, CH 3 0H, should be
   added to 1,000 grams of water to give a solution that will
   freeze at -10°?


4. What is the molecular weight of a substance, 3 grams of
   which dissolved in 50 grams of water gives a solution freezing
   at —0.93°? The solution does not conduct electricity.


5. Pure benzene freezes at 5.48°. What is the molecular
   lowering of the freezing point for benzene if a solution of
   6.4 grams of naphthalene, CioHs, in 100 grams of benzene
   freezes at 3.03°?