Question

Sterling silver is a solid solution of silver and copper. if a piece of a sterling silver necklace has a mass of 105.0g and a volume of 10.12 ml, calculate the mass percent of copper in the piece of necklace. assume that the volume of silver present plus the volume of copper present equals the total volume.

Answer 1

Density for Cu: 8.96 g/ml 
Density for Ag: 10.5g/ml

First set up an equation: mass = density * volume 

8.96 * x + 10.5* (10.12 - x) = 105.0 

The density of the Cu (8.96) times x (the amount of copper) added to the density of Ag (10.5) times voume of silver (10.12 - the amount of copper) should equal the total weight. 

Solving for x:

x = 0.818 mL 

So 
mass of copper = 8.96 * .818 = 7.33 
mass percent of copper = 7.33/105 * 100% = 6.98%