182 ALKALI AND ALKALINE EARTH METALSapply suction and press out the last possible drops of liquid.
Repeat the washing with another 15 cc. of distilled water. The
product may now be considered to be "commercially pure"
although it still contains an appreciable amount of chloride.
Test the preparation for chloride by dissolving about 0.1 gram in
5 cc. of distilled water, adding an excess' of dilute nitric acid and a
few drops of silver nitrate solution. Transfer the product to
a 4-inch porcelain dish, taking care not to include any of the
filter paper, and allow it to air-dry completely if it is to be pre-
served as sodium bicarbonate. If it is to be converted to the
carbonate it is not necessary to wait for complete drying. Place
the dish on an iron wire gauze on a ring stand, and adjust a gas
flame 2 inches high the top of which is | inch below the wire gauze.
Continue the heating in this fashion until the product appears
dry. Then place a watch glass over the dish to retain the heat in
the upper layer of the powder and continue the heating with
frequent stirring until escape of gas (seething) ceases. One-half
hour's heating with the low flame as described should suffice to
decompose the bicarbonate (200°) and avoid melting the car-
bonate (851°) and causing it to cake together and stick to the dish.
Put up the preparation in a 2-ounce cork-stoppered bottle.
QUESTIONS- What is the purpose of washing the product with water?
How much sodium bicarbonate is lost in the mother liquor and
the wash water (see solubility table)? - Why must the solution be acidulated with nitric acid before
testing with silver nitrate? - Why cannot potassium bicarbonate be effectively prepared
from potassium chloride by the ammonia process? (Look up
the solubility of potassium bicarbonate.) What process may
be used to prepare potassium carbonate from this source? - Write the intersecting ionic equation for the recovery of
ammonia from the ammonium chloride liquors. - What becomes of the ammonium chloride still clinging to
the sodium bicarbonate preparation when the latter is heated to
convert it to the carbonate? - Define an acid salt. Compare the acidity of NaHSC>4 and
NaHC0 3. Write equations for reactions in which these acid salts
are showing their acid character.