# Chemistry

posted by on .

Gold is alloyed with other metals to increase its hardness in making jewelry.

Consider a piece of gold jewelry that weighs 9.85 g and has a colume of 0.675 cm cubed. The jewelry contains only gold and silver, which have densities of 19.3 g/cm cubed and 10.5 g/cm cubed, respectively. Assuming that the total colume of the jewelry is the sum of the columes of the gold and silver that it contains, calculate the percentage of gold (by mass) in the jewelry.

The answer is 61.5% Au, but I have no idea whatsoever how to find that answer...

massgold + massmetal= totalmass

you are given the total mass.
Volumegold + volumemetal= total volume
you are given the total volume

from the first...
massgold + massmetal= totalmass
densitygold*volumegold + densitymetal*volumemetal=9.85

So now you have two equations:

Volumegold + volumemetal=.675
19.3*volumegold + 10.5*volumemetal=9.85

solve for the volume of gold (any method you choose..I recommend substution)
Then, solve for the mass of gold from volume and density, then finally, percentage.

Repost if you get stuck. Nice problem