Wash and dry the "gold" penny. Clean the pennies in concentrated HCl. Watch zinc filled pennies (after 1983) to make sure the HCl doesn’t get to the zinc and dissolve it. Stir NaOH/Zn mixture with a ...

relative atomic mass of Zn = 65.4 relative formula mass of HCl = 1.0 + 35.5 = 36.5 total relative formula mass of reactants = 65.4 + (2 × 36.5) = 138.4 total relative formula mass of desired ...