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In this experiment, an electrochemical cell is used
to remove copper from a dilute copper sulfate feed solution. The copper is
plated onto a cathode bed of stainless steel balls.
The effluent copper level
is determined by spectrophotometry, while a potentiometer and digital displays
are used to set the cell voltage and current. Cell current is supplied by a dry
cell battery. The basic data are steady state values of current, voltage, and
the feed and effluent copper levels. From these data the current efficiency can
be determined, and the onset and magnitude of hydrogen evolution can be studied
as a function of voltage.
At a given flow rate the students
can determine the current, effluent copper concentration, and current
efficiency as functions of cell voltage. If this is done for several flow
rates, significant information on the process can be obtained. Alternately the
effect of flow rate on voltage, current and copper level, for a fixed
potentiometer setting, may be determined.
The time constant of the process
is two to ten minutes, so that a number of steady state runs can be made in a
typical laboratory period. At higher voltages hydrogen evolution is evident,
but at rates entirely compatible with safe operation.
The experiment is also supplied in a computer controlled version, where
continuous monitoring of effluent provides feedback for continuous control of
feed rate and cell current, as well as data recording.
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