A 0.411g sample of powdered copper mixed with an inert, soluble additive was fully consumed by 23.4ml of 0.602M nitric acid, producing copper(II) nitrate, water and nitric oxide (NO) gas. What was the percent copper (by mass) in the sample?
3Cu + 8HNO3 ---> 3Cu(NO3)2 + 2NO + 4