Galvanic Cell exp

[Sassi]

Hi people,

We are having massive problems with this experiment, it never works We have tried different concentrations from 0.1M to 1M, still doesn't work... So thinking that it might be a problem with the salt bridge, we use a bit of filter paper (2 x 15 cm) soaked in KNO3 solution, what do you reckon and what do you use for the salt bridge??? Also could there be a problem with the electrodes? They are quite old, tried sanding them, still no better... HELP

[lada]

We use saturated KNO3 for the bridge, yes, use filter paper,
electrodes must have very clean terminals and we use graphide, Zn, Ni, Cu and for the solution 0.1 M NaCl, CuSO4, ZnSO4.
Make sure your voltmeter is VERY sensitive, maybe use galvanometer, or mV, as the voltage produces is tiny.
Good luck
Lada

[smiley]

We use KCl on our salt bridge, and a multimeter, coz they're more sensitive.

[Ocker]

Yes use digital multimeters, because they don't draw any power from cell to give reading, they operate with a comparator, that adjusts voltage from internai battery, till it equals source

[rae]

Sorry to side track the subject, but Graeme where did you get the digital multimeters??

Lorrae

[Ocker]

Jaycar or Dick Smiths for a few dollars more
You can get them for about $15 each but do yourself a favour get auto off version for about $30 save it in batteries they also give a discount for 3, 6 or more

[Sassi]

Hi all,

Thanks for your replies they were most helpful. The teacher and I have decided to do the saturated KNO3 salt bridge, we used 0.1M and try with both multimeters and galvanometer to see what works best for us. A good clean of the electrodes & terminals too might help us solve our problem, problem is, when will I find the time to clean them

Sassi

[Loopy]

The 25th hour of the day?

Lou.

[J]

Or hand the kids some sandpaper and get them to do it!

Julie

[Tina]

Very funny! 25th hour of the day! Just think what you could get done in the 26th and 27th hours as well!!

Another question about galvanic cells (and lemon batteries).

I can get voltage readings but not current.

My teacher wants a galvanic cell to run a light bulb to show changes from chemical to electrical energy. I saw on u-tube a video of how to make a lemon battery (set up in series) with enough voltage to run an LED light. Tried that and again got voltage but no current and therefore no light in the bulb. Tried galvanic cells in series. Again no current. only voltage. The bulb works when attached to battery. Can get 7 volts if I connect enough cells or lemon wedges in series. Someone suggested sprinkling bicarb soda on the lemon to get the current?

My galvanic cell had zn and cu electrodes, zn and cu sulfate solutions and a KNO3 salt bridge. Used copper coins and galvanised nails as electrodes in the lemon battery. I'll have to set it all up again (tried last friday) but don't think it is the terminals. Will try cleaning them though. any other ideas?

Thanks
Tina

[Ocker]

Did you try reversing leads on led thats light emitting diode and diodes are polarity sensitive

[Tina]

Yes. I tried it both ways
thanks
Tina