STANDARDIZATION OF SOLUTIONS 79the normality of the HC1. Calculate also the exact normality of the
NaOH.
Preserve these standardized solutions for the later determina-
tion of the yield of NaOH in the electrolysis of brine (page 185)
and in the preparation of NaOH (page 183).
Specific Gravity. The specific gravity of a liquid is the ratio of
its weight to the weight of an equal volume of pure water at the
temperature of its maximum density (4°C). This applies alike
to pure liquids such as acetic acid and to solutions.
Substances dissolved in water change the specific gravity, and
since specific gravity is one of the properties of a liquid most easily
measured with great precision, it is much used by chemists for
determining the concentration of solutions which are known to
contain only a single dissolved substance.
Tabulations have been prepared for many common substances
such as hydrochloric acid, sodium hydroxide, ammonia, and al-
cohol, in which the specific gravity and the corresponding percent-
age by weight of the solution have been placed in parallel columns
covering the whole range from pure water to saturated solution.
For example, if we wish to find the concentration of a given solu-
tion of NaOH, we measure its specific gravity which proves to be
1.390. Opposite this specific gravity in the table we find (inter-
polating if necessary) the percentage composition by weight, and
we derive the concentration as follows:
SOLUTION OF NaOH
Specific gravity 1.390 Percentage by weight 36.00
Weight of 1 liter = 1,000 X 1.390 = 1,390 grams
Grams NaOH per liter = 1,390 X 0.3600 = 500.4
F.W. of NaOH per liter = 500.4/40 = 12.5
Normality of NaOH solution = 12.5
The Use of the Formula Weight Method in Chemical Arithmetic.
A chemical equation tells not only what substances, but also how
much of these substances, are involved in a chemical reaction.
For example, the equation
Na 2 CO 3 + Ca(0H) 2 -» CaCO 3 + 2NaOHreads: 1F. W., or 106 grams, of sodium carbonate reacts with 1F. W.,
or 74 grams, of calcium hydroxide to give 1 F.W., or 100 grams, of
calcium carbonate and 2 F.W., or 80 grams, of sodium hydroxide.