# Measuring the Resistance of a Solution

#### Vikas06

Joined Jun 7, 2005
2
Hey,

I am trying to measure a solution's (electrolyte) resistance, but I am not sure how to do it with small error. If I insert a multimeter's probes into the solution, the probes will essentially create a capactitive polarization effect which would create error in my measurement. I have seen some devices that measure electrolytic resistance, but they are beyond my price range. Any help, or suggestions would be greatly appreciated.

Vikas

#### beenthere

Joined Apr 20, 2004
15,819
Hi,

You are trying to measure conductivity, since this is current flow in a solution. The effect you would see if using something like the DC current frm an ohmmeter is the ions plating onto the positive meter probe. This will affect the reading by removing ions from the solution and lowering conductivity, and also plating a non-conducting material onto the positive probe which will put an increasing error into the reading.

You have to use AC to measure conductivity. Any small transformer with an output in the 6 - 12 volts range will work. Place a known resistance in series with one of the measuring electrodes, and measure the current in the total circuit. One variable is the area of electrode exposed in the beaker. Conductivities are expressed as siemens/cm3.

Conductivity, especially in water, is interesting to measure.

#### Vikas06

Joined Jun 7, 2005
2
Thanks for the advice, but I still have one quick question. Since I only want the resistive component (I am not interested in the reactance) could I use a high frequency source to essentially remove any reactance? And I would imagine I would take the Vrms / Irms to get the resistance value?

Once again thanks,

Vikas

#### _Raven_

Joined Jun 3, 2005
10
Originally posted by beenthere@Jun 7 2005, 08:41 PM
Hi,

You are trying to measure conductivity, since this is current flow in a solution. The effect you would see if using something like the DC current frm an ohmmeter is the ions plating onto the positive meter probe. This will affect the reading by removing ions from the solution and lowering conductivity, and also plating a non-conducting material onto the positive probe which will put an increasing error into the reading.

You have to use AC to measure conductivity. Any small transformer with an output in the 6 - 12 volts range will work. Place a known resistance in series with one of the measuring electrodes, and measure the current in the total circuit. One variable is the area of electrode exposed in the beaker. Conductivities are expressed as siemens/cm3.

Conductivity, especially in water, is interesting to measure.
[post=8304]Quoted post[/post]​

Plating will only occur at high current rated at around 1mA/cm2. Forcing at around 1uA at the probe. I don't advice AC coz all AC parameter from the solution will arise.
Capacitance is on of the issue here.

I advice to force 1uA at the solution connected with 500K. and measure the voltage drop across 500K and subtract it from the total voltage force at both probe and divide it with 1uA. With a known molality of solute you can determine also the resistance /molar.