MadSci Network: Chemistry

Re: How would i measure electrolytes in drinks?

Date: Sun Jan 18 05:53:28 2009
Posted By: Cesar Prado-Fdez, Secondary School Teacher, Science
Area of science: Chemistry
ID: 1230590095.Ch

The water is not a very conductive substance itself. The fact that we know
we should not mix water and electricity is that water can dissolve many

The substances that dissolve better in water are ionic compounds. These are
substances composed by ions, positive (cathions) and negatively (anions)
charged particles. These ions are separated when dissolved in the water.
This “ionic solution” is what we call an electrolyte and because it
contains positive and negatively charged particles it can now conduct
electricity. And it is an obvious idea to relate the behaviour of the
electrolyte to an electrical current with the concentration of these
particles in the solution.

First of all we have to model a circuit, where the electrolyte can be
pictured as a resistance. By measuring that resistance of the electrolyte
we can therefore calculate the concentration of ions in the solution.

But when we study the resistance given by the electrolyte we can see it
does not work as just a simple resistor but if we want to take accurate
mesures we have to take into account at least another element, a capacitor,
connected in series (the simplest model). The problem is that a capacitor
stops the current so we cannot use a dc current to make the measurements;
we need to use alternating current, ac, and the resistance is called
impedance instead (so we do not confuse with the simple one)

In order to measure the impedance or its inverse, conductivity, we need a
EnC (Electrical Conductivity) meter (

“The common laboratory conductivity meters employ a potentiometric method
and four electrodes. The electrodes are usually cylindrical and arranged
concentrically. The electrodes are usually made of platinum metal. An
alternating current is applied to the outer pair of the electrodes. The
potential between the inner pair is measured. Conductivity could in
principle be determined using the distance between the electrodes and their
surface area using the Ohm's law but generally, for accuracy, a calibration
is employed using electrolytes of well-known conductivity.”

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