Hello all -
I am trying to design a lab that will show my students some concepts of chemical conservation, percent yield, and the differences between metals and metal ions. To do so, I have them react copper with an oxidizing agent to yield copper ion. Then I react this copper ion solution with zinc metal in order to return copper ion to copper metal. In the final reaction, I react any remaining zinc metal with 6M HCl. I am having two problems with the lab.
1) Oxidizing Agent. Typically, this reaction is done with silver nitrate in order to produce silver metal and copper (II) nitrate. It reacts quickly enough and completely. However, the cost for silver nitrate (about $250/100g, and I need ~75g/lab) has lead me to look for another agent. I tried 6M Nitric acid, but the reaction has many problems, not the least of which is the NO gas that is released and converted to NO2 (it is also slow and acid tends to be left over). So my question is what soluble oxidizing agent would work quickly, completely, and do so relatively inexpensively and safely?
2) Assuming I make nice copper (II) ion in water - evidenced by a deep blue color - I add 20 mesh zinc metal (probably from the 80's, so there is likely a coating of zinc oxide). Very exothermically, copper metal appears (much of it stuck on the excess zinc metal) and the solution goes clear as zinc ion in water is clear. I filter the copper out and immediately wash it down with 6M HCl to react the remaining zinc. To speed drying, I rinse the product with acetone and dry it in a 60?C oven. The product, however, is much more red-brown than copper metal would be, suggesting incomplete reduction to copper (I) oxide. Why is this happening?
Thanks so much for your thoughts and ideas!