Australia's Science Forum

Does anyone know what the plating is on these items? Is it nickel, tin, chrome or other?
A teacher here freaked out because kids were doing a conductivity prac, putting leads with alligator clips attached to the banana plugs into a beaker of dilute acid then rinsing them in a beaker of water. He decided that the rinse water had become yellowish because the clips/plugs were chrome plated and the acid was stripping this off and producing hexavalent Chrome in solution... a real nasty!
Supplier didn't have a clue - anyone? How can you tell between the coatings?

I am answering my own query...
Supplier got back to me and the alligator clips and banana plugs are NICKEL plated...
pheww..

Thanks, Sunray

Ok I said 'phew' before I realised the full situation...

Nickel(II) is nastier than chrome(III). cause severe skin problems, so avoid any skin contact ... look it up!
SO - all of those times when students and teachers dunk the alligator clips and/or banana plugs into an acid solution, they are potentially dissolving the nickel and forming Ni(II) compounds...

perhaps all those who use RiskAssess should ask about this hazard - perhaps should be incorporated into the Risk assessment protocol.

[By the way - you can precipitate nickel and chrome from the solution using NaOH - at the right pH , and then it can be stored as a hazardous waste solid for disposal later]

What pracs require putting them in acid?

in a perfect world - none! but often teachers will just be lazy and tell the students to just attach the leads to transformer and dip the ends into the solution, or the alligator clips attached to the banana plugs into the solution. I have had the teacher of senior Science get students to just use the banana plugs to dip into cosmetics, like face cream etc, to test the conductivity. alligator clips are seen as the disposable item, and because of that I seem to be always buying them. I don't think anyone had twigged to the dangers before this - or hadn't mentioned it.
Paper clips are similarly dangerous - they are either chrome or nickel plated. teachers use them for all sorts of things in the labs.
Just be aware and careful.

Can you give them a telling off (the teachers) for mis-using equipment?

Its akin to taking a spatula to stir a solution, but dipping your fingers in instead