Ask A Scientist Chemistry Archive

name         Laura S.
status       student
age          14

Question -   In my science class, we did this experiment with salt,
water, a long small beaker, two connecter wires, a beaker, a battery, and
a paper clip. You put salt in a beaker, and then out some water in. Take
one wire, and attach a P.C. (paper clip) to the end of it. Do the same
for the other wire. Then take the small beaker and fill it all the way
with some of the salt water in your big beaker. put your thumb over it,
and submerge it in the water, so the water is still in it, and then take
one of the P.C attached to the wire and put that in the small beaker so
it will not float out. Then, take the second P.C./wire and just put that
anywhere in the water. Connect the wire that is in the small beaker to
the positive side of the battery, and the one that is just hanging around
in the water to the negative side of the battery. The one inside the
small beaker should be bubbling, and the small beaker should be catching
most of them. The water will start to turn yellow, then orange, then kind
of green, and then it will be sort or brownish. What I would want to
know, actually, is what is in salt, and what makes the brown color?
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Your detailed description of the experimental setup is to be commended. It
is your attention to detail that often is lacking in young scientists-to-be.

The culprit here is not the salt (NaCl). It is the paper clips and also
possibly the wire. Paper clips are usually made of iron, with often a chrome
or nickel plating to inhibit corrosion. The wire, I assume is copper. The
yellow ---> orange ---> brown sequence of colors is very likely due to the
electrolytic oxidation of the iron in the paper clips (rust). The color
change is due to the increasing concentration. The green could be due to the
formation of Ni(+2), Cr(+3) and/or Cu(+2) all of which are green or blue,
depending upon the concentration and other details.

Vince Calder
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