Solubility
Super-saturated
solutions of the respective compounds were prepared by adding
ACS reagent grade salts into deionized water in 500 mL glass
bottles that were approximately at the selected experimental
temperature. Addition continued until an excess of solid appeared
which completely covered the bottom of the container. The bottles
were closed with teflon stoppers and immersed in constant temperature
baths whose temperatures were adjusted to the respective experimental
value at which the salt's solubility was to be determined.
The bottles were kept in the constant temperature baths for
3-4 days. At the end of this period, a pipette that was warmed
with a heat gun to slightly above the experimental temperature
was inserted and a portion of the saturated solution was withdrawn
and analyzed.
For the analytical methods using weight
analysis and AA spectroscopy, A grade, 1 mL pipettes
were used. For analysis by titration, A grade 25
mL pipettes were used.
Weight analysis:
1 mL of saturated solution was transferred
to a clean, dry, container whose tare weight was determined.
The container plus solution were weighed and the mass of solution
determined. The solution was evaporated to dryness in an oven
at 105-110 oC and the mass of the dry salt determined.
Analysis
of lithium chloride (LiCl) by titration:
A 25 mL aliquot of the saturated lithium
chloride solution was pipeted into a 500 mL voulmetric
flask and diluted with deionized water to 500 mL.
Samples were titrated with standard silver
nitrate solution using 5% Potassium Chromate as an indicator
(10 drops per sample).Titrant was added until a pinkish
yellow persisted at the end point. (Potassium chromate
indicates the end point for the silver nitrate titration
of chloride by the formation of silver chromate, which
is red. Silver chloride, which is a white precipitate is
quantitatively produced before the red silver chromate
is formed.)
Analysis of copper(II) sulfate by
atomic absorption spectroscopy (AA):
AA
methodology:
1 mL of saturated solution was transferred
to a 1 L volumetric flask and diluted to 1000 mL with deionized
water.1 mL of this stock solution was diluted once again
to 100 mL with deionized water in a volumetric flask to
bring the concentration of Cu into a suitable cocncentration
range for analysis.
AA spectroscopy data were obtained by using
a Perkin Elmer Atomic Absorption Spectrometer, model 100
at standard atomic absorption conditions for Cu: wavelength:
324.8 nm, slit 0.7 nm, relative noise: 1.0, characteristic
concentration check: 4.0 mg/L, linear range: 5.0 mg/L;
flame: air-acetylene, oxidizing (lean, blue).
Experimental
Rapid-Growth Apparatus
Adaptation of Dr. Zaitseva's method for
fast-growing KDP crystals produced single crystals of potassium
chloride and copper(II) sulfate pentahydrate.
Several experiments were
successfully conducted using the apparatus illustrated
in the following images. A pyrex coffee pot was placed
on a heating plate and heated. Saturated solutions of the
respective salts were prepared in the coffee pot at a temperature
selected from the salt's solubility curve. A student fabricated
lucite platform with a hexagonal bolt having a seed crystal
of the salt fastened to its surface was placed in the bottom
of the coffee pot. A mechanical stirred slowly agitated
the solution which was sealed with aluminum foil. As the
crystal grew, the temperature was lowered.
Potassium Chloride
(KCl) Crystals
Copper(II)
Sulfate pentahydrate- monoclinic crystal
