184 ALKALI AND ALKALINE EARTH METALSMaterials: anhydrous sodium carbonate, Na2CO 3 , 53 grams =
0.5 F.W.
slaked lime, Ca(OH)2, 50 grams.
Apparatus: 8-inch porcelain dish.
suction filter and trap bottle.
burette with standard HC1.
10-cc. pipette.
300-cc. Erlenmeyer flask.
iron ring and ring stand.
Bunsen burner.
500-cc. bottle with rubber stopper.Procedure: Dissolve the sodium carbonate in 300 cc. of water,
and stir the slaked lime into another 300 cc. of water, making milk
of lime. Bring the carbonate solution to boiling in the 8-inch
dish and pour the milk of lime slowly with stirring into the boiling
solution. Let the mixture boil 15 minutes and then filter, using
a suction bottle (see Note 4 (6)). Measure the volume of the solu-
tion of caustic alkali obtained and preserve it in the rubber-stop-
pered bottle.
Determine the Strength of the Solution. With a pipette measure
10 cc. of the preparation into a 300-cc. Erlenmeyer flask, add
100 cc. of distilled water, and titrate against standard HC1 using
phenolphthalein as the indicator. (See Experiment 6, page 75.)
Carry out a duplicate titration with a second 10-cc. sample, and
take the average of the results to give the normality of the solu-
tion. Label the bottle with the number of cubic centimeters of
the solution, with its normality, and with the actual amount in
grams of the hydroxide.
QUESTIONS- The calcium hydroxide used in causticizing is soluble only
to the extent of 1.7 grams per liter. Explain how, in spite of its
limited solubility, the required amount can enter into reaction. - Explain why the solution obtained contains practically no
calcium ions although an excess of calcium hydroxide, which is
appreciably soluble in pure water, has been used for causticizing.