(Disclaimer: This post is for purposes of creating fine artwork! We are not attempting to create bullion for profit.)
In my last post (pt I), I explored getting the zinc out of a penny intact while losing the copper. If you have not read that post first, I suggest you do now for background on the penny composition, etc.
In this post we are going to do the opposite, we will remove the zinc from the middle while trying to leave the fragile copper shell relatively intact.
In full disclosure, I attempted a method that I read about on the internet to remove the copper. I discovered after the fact that this meant removing the copper to keep, not removing to expose the zinc.
This turned out to be a great lesson in the reactivity series which lists the order that elements are likely to react. Zinc is generally more reactive than copper. So in this example the solution we create will attack the zinc instead of the copper.
We will soak the pennies in diluted hydrochloric acid (bought more often as muriatic acid, usually for swimming pools).
Now I honestly should have stopped and thought why the first step is to score the pennies around the edges. I just took at steel wirecutter and put four notches around each penny at 12, 3, 6, and 9 o'clock. The reason for this is obviously to give the solution some access to the zinc. Otherwise, the copper will just sit there protecting the pennies.
Into my beaker, I poured about 50ml of 20 baume (31.5%) HCl. Then I added roughly 100ml of water to dilute to around ~10%. Now drop the scored pennies into the diluted acid and watch the bubbles until the reaction is done.
I never got the reaction equation from the internet because I was reading about attacking copper, not zinc. So I will attempt to determine the equation here.
We know the reactants are Zn and HCl in H2O, so it should be something like...
Zn + HCl + H2O -> a vigorous gas, a compound of Zn, and water
I am fairly certain this reaction, balanced, is:
Zn + 2HCl -> ZnCl2 + H2
Once again, note this reaction forms hydrogen gas most likely, so please do this in a vented area and take all safety precautions. I made a lot of gas doing this!
ZnCl2 (zinc (ii) chloride) has no natural analogue. It is supposed to be a white powder, but I made a mess of blackish stuff. This could be for any number of reasons, but most likely that I did not fully react the zinc before finishing my experiment. The black is likely remaining powdered zinc and the white powder dissolved in the solution.
Copper does not react because hydrogen is more reactive than copper, so it would stay bound to the chlorine. Zinc does because it is more reactive than hydrogen and thus swaps places in what is known as a single replacement redox reaction.
The elemental zinc with a neutral charge loses two electrons (oxidation), and the hydrogens gain one each (reduction) so that it can bond and form hydrogen gas.
We can remember this as OIL RIG: Oxidation is loss, Reduction is gain (loss/gain of electrons)
When both oxidation and reduction happen together, we call it a redox reaction.
When the reaction had slowed down, I fished out the pennies. They were very lightweight and fragile. Recall the copper shell is only .06g. Mine weigh a bit more because I did not fully oxidize the zinc.
Thanks for reading,
Paul
p.s. It has come to my attention that some people would like to repeat these experiments without the hassle of finding the chemicals and/or having to buy too much, etc. I will try to keep an Ebay store alive (seller: cinnabarminerals) that offers low cost and related material for the purpose of enabling education. I will title offerings "Brave New Chemist Science Pack - (related Blog post name)." You can always comment and ask where to buy certain equipment too.
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