Lab Report Electrical Current in Water

[meisadam]

hi

i did an experiment about electrical current in water depending on the amount of ions for the g4p in physics.

for each water the intensity/voltage relation was proportional, but the graph never started at 0,0 but was shifted right by different values.

my teachers says this is no energy dissipation in the circuit or sth like that, but the nature of the process. he gave me hints, to start looking at recombination of ions and potential barrier, but I could not find any explanation. any help is very welcome

[Drake Glau]

What do you mean by amount of ions first of all? What did you do to test the water?

[meisadam]

we investigated the I/V relations in different mineral waters and then came up with a formula for I depending on V and amount of ions per 1 liter.

[Drake Glau]

You changed two variables though? I'm confused.

[meisadam]

yeah, we made the regular I/V measurement.

and repeated it in different kinds of mineral water.

the outcome was the formula for intensity depending on voltage and mineralization.

my question is in the first post

[Drake Glau]

There is no question in your first post

[meisadam]

the intensity/voltage relation was proportional, but the graph never started at 0,0 but was shifted right by different values.

my teachers says this is no energy dissipation in the circuit or sth like that, but the nature of the process. he gave me hints, to start looking at recombination of ions and potential barrier, but I could not find any explanation. any help is very welcome

question:

why the I/V graph never started at 0,0

[dessskris]

question:

why the I/V graph never started at 0,0

internal resistance, I guess?

V = E - Ir

Ir = -V + E

I = -V/r + E/r

if you look at it carefully, it's actually:

I = mV + c

which is

y = mx + c

the c is non-zero constant.. it's E/r. therefore the graph does not pass through the origin

[meisadam]

well, the voltages were read from the voltmeter in the circuit so I guess it's not the internal resistance.

AND my teacher, who is a genius says it is the nature of the process.

maybe some chemistry guys could solve it, he says that if you put even a carbon electrode into mineral water, some reaction takes place which creates p.d. between the electrode and water, yet still, thanks for the input!

[dessskris]

oh hahaha sorry I didn't read the question carefully

yeah it's electrolysis. if you put carbon electrodes into water and pass through electricity, the H+ and OH- ions will be discharged. if I am not mistaken, Hydrogen gas will be produced at the cathode and Oxygen gas will be produced at the anode.

Using the Nernst equation the electrode potential can be calculated for a specific concentration of ions, temperature and the number of electrons involved. For pure water ( pH 7):

• the electrode potential for the reduction producing hydrogen is −0.41 V
  
• the electrode potential for the oxidation producing oxygen is +0.82 V.

(http://en.wikipedia.org/wiki/Electrolysis)

I don't know if that helps, but perhaps it gives you some ideas of the process that actually takes place