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Laboratory work
Experiment 1: Determination of Ca
2+
ions by using ion exchange.
Attention! During the experiment with cation exchanger, it is necessary
to constantly monitor that there is a liquid layer of 1–2 mlabove the cation
exchanger.
A column was prepared with the cation resin in the H+–form (the cation
exchange resin was pretreated with a solution of hydrochloric acid)for doing
the experiment. Opening the tap, drain excess fluid. About 2 ml is left over the
cation exchanger. Then 20 ml of a CaCl2 solution of unknown concentration
are passed through the column in small portions. The liquid passing through the
column is collected in a large flask. After this, the beaker is washed with 20 ml
of distilled water, which is also passed through the cation exchanger. Wash wa-
ter is also collected in a large flask.
The entire solution collected in the flask is titrated with a 0.1 M solution of
NaOH in the presence of phenolphthalein until a slightly pink coloration appears.
The analyzed solution of CaCl
2
passes through the cation exchanger in
the H
+
-form, the calcium ions replace the hydrogen ions. The number of
hydrogen ions is equivalent to the amount of calcium ions. Mass of Ca
2+
(in g)
in the analyzed solution of CaCl
2
is calculated by the formula:
(
)
2
2+
(NaOH) (NaOH)
(Ca )
1000
eq
eq
C
V
M Ca
m
+
⋅
⋅
=
Answer the questions: what are the processes of exchange and regeneration
of the cation exchanger? To which types of chromatography on the technique of
execution and on the mechanism of the process is this work?
Experiment 2. Separation of a mixture of Cu
2+
and Fe
3+
cations by
chromatography on paper.
Application of a separated mixture of ions. Apply a drop of a solution
containing Cu
2+
and Fe
3+
ions on a narrow strip of filter paper at a distance of
1–1.5 cm from the bottom edge. After applying a drop of solution, the strip of
paper should be slightly dried in air.
Separation of a mixture of ions. A strip of filter paper is fixed in the holder
and lowered into a glass with water. Herewith the bottom edge of the paper
strip should touch the surface of the water only (depth of immersion of a strip
of paper 2–3 mm). Separation of ions ends when the water rises to the top edge.
A strip of paper is taken out of the glass and dried in air.