we need to make sensors at school for physics coursework...?

Question

we have to make a sensor on our own for our physics coursework. the teacher gave us loads of ideas and i chose (now i'm wondering why i chose it) a concentration sensor. I decided to use CuSO4 as my salt whose concentration i'd measure using the sensor. I need to use a potential divider and a voltmeter in my sensor. what formulas would i need for calculating concentration of a salt from current, voltage and resistance? and how could i set my sensor up? any ideas at all as to any websites on sensors or anything helpful will be appreciated.

Answer 1

The molar conductivity of 1/2 CuSO4 at 25 degrees C is 133.6 at infinite dilution, and for higher concentrations (mol/L^3):
conc conductivity
.0005 121.6
.001 115.2
.005 94.02
.01 83.08
.02 72.16
.05 59.02
.1 50.55

Be sure to use inert electrodes. Gold or platinum would be best, but don't spend the money just for homework. Keep the currents small so you're not disturbing the solution. Note how the conductivity is defined and try to think of a setup that would help improve your measurement accuracy and ease of calculations. Like, have your electrodes completely cover both ends of a filled soda straw, since your measurement of length will be more accurate than your measurement of cross-section area.

You're probably better off NOT looking at websites on sensors. Rather, think about how you could invent one and how you could maximize its accuracy.

Answer 2

Take 1 liter of distilled water. Insert the voltmeter probes and measure the resistance. (Since it's distilled I would think it would be infinite)

Add x grams of your salt and measure the resistance each time you add the salt. If you can calculate the PPM (parts per million) all the better or just make a graph showing the change in resistance for each amount of salt you enter. Be sure each addition of salt is equal.

Do the same with NaCl (table salt) and you can compare the NaCl curve to the CuSO4. The higher the concentration of the salt, the lower the resistance should be. Your teacher can then put some CuSO4 in a beaker and you should be able to tell him/her the concentration by measuring the resistance and using your graphs.

Anyway, that's my suggestion.

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