Synthetic Inorganic Chemistry

60 WATER AND SOLUTION

is the first to separate spontaneously. However, below 33° the

heptahydrate is more soluble than the dekahydrate, and, therefore,

with the seed crystals added, and equilibrium established with the

latter salt, the heptahydrate again dissolves.

Materials: anhydrous sodium carbonate, Na 2 CO 3 ; 106 grams

= 1 F.W.

Apparatus: 500-cc. flask.

5-inch funnel.

8-inch crystallizing dish.

8-inch glass plate to cover dish,

porcelain filter plate.

Bunsen burner,

iron ring and ring stand.

Procedure: Place the sodium carbonate and 250 cc. of water in
the flask and warm it to just short of the boiling point until the
salt is dissolved. See Note 7, page 13. Filter the hot solution
into the crystallizing dish, keeping the dish covered with a glass
plate except where the stem of the funnel enters. When the solu-
tion has cooled below 33° add a few crystal fragments of the deka-
hydrate. Set the dish, completely covered, in your desk. After
6 hours or longer separate the crystals from the remaining liquid by
pouring the contents of the dish into a funnel in the bottom of
which is placed the perforated porcelain filter plate without any
paper. It may be possible to get additional crystals from the
mother liquor by cooling it still more. After the crystals have
drained dry them on paper towels. See Note 9 (6), page 15. The
crystals should not be left more than over night wrapped in the
paper towels. When they are dry place the crystals in an 8-ounce,
cork-stoppered bottle.

QUESTIONS

1. What reasons have you for believing that the water in crystal
   hydrates is in chemical combination with the salt?


2. How could anhydrous sodium carbonate be prepared from
   the hydrate?


3. How could the monohydrate, Na 2 CO3-H 2 O, be prepared?