Whether in the UK or in the US, the mass of the copper in a copper alloy penny can be determined. If you are in the US, just note that on the lab sheet, a penny is identified as a "1p piece." The penny is dissolved by young chemists in nitric acid. They treat the resulting solution in order to form an iodide precipitatet. Finally, they titrate the solid with sodium thiosulphate and then use the amount to calculate the mass of copper. This is a top-notch lab to challenge your chemists with!