If you take a sample of the coin and mix it with aqua reqia (a 5:1 solution of HCl and conc. HNO3) the metals will dissolve. Gold is oxidised by the nitric acid to Au3+, which is complexed by the chloride to Au(Cl4)- (can’t do subscripts). This drives an equilibrium forward, causing more gold to dissolve.
Gravimetric method: By boiling with hydrogen peroxide, the gold will precipitate out, but I’m not sure what other metals will. Copper definitely will not. By filtering the solution and igniting to dryness, the amount of gold can be determined gravimetrically.
Atomic absorption: A more selective test, dilute the gold solution and use in an AA apparatus. Compare to a calibration curve and compensate for dilution factors.
April 2nd, 2009 at 6:06 pm
Jesse
If you take a sample of the coin and mix it with aqua reqia (a 5:1 solution of HCl and conc. HNO3) the metals will dissolve. Gold is oxidised by the nitric acid to Au3+, which is complexed by the chloride to Au(Cl4)- (can’t do subscripts). This drives an equilibrium forward, causing more gold to dissolve.
Gravimetric method: By boiling with hydrogen peroxide, the gold will precipitate out, but I’m not sure what other metals will. Copper definitely will not. By filtering the solution and igniting to dryness, the amount of gold can be determined gravimetrically.
Atomic absorption: A more selective test, dilute the gold solution and use in an AA apparatus. Compare to a calibration curve and compensate for dilution factors.
Hope this helps.