Calculating percentage of mass in an alloy

K

kwikness

New member
Joined
Sep 12, 2007
Messages
4
I have this problem for a chemistry quiz. I can solve simple density equations easily (density = mass/volume) But this one is insane and I have no idea how to solve it. Here goes:

You have a piece of jewelry that has a mass of 9.35g(grams) and a volume of 0.654cc(cubic centimeters). Assuming that it is an alloy of silver and gold, which have densities of 10.5g/cc and 19.3g/cc respectively. Assume there is no change in volume when the metals are mixed. Calculate the mass by % of gold in the alloy.

Could someone please give me a detailed, step-by-step explanation on how to solve this type of problem? Thank you for any help!!

,Kyle
 
kwikness said:
I have this problem for a chemistry quiz. I can solve simple density equations easily (density = mass/volume) But this one is insane and I have no idea how to solve it. Here goes:

You have a piece of jewelry that has a mass of 9.35g(grams) and a volume of 0.654cc(cubic centimeters). Assuming that it is an alloy of silver and gold, which have densities of 10.5g/cc and 19.3g/cc respectively. Assume there is no change in volume when the metals are mixed. Calculate the mass by % of gold in the alloy.

Could someone please give me a detailed, step-by-step explanation on how to solve this type of problem? Thank you for any help!!

,Kyle
Click to expand...

Use

Assume

Volume of Gold in the jewelery = G

mass of Gold in the jewelery = 19.3 * G

Volume of Silver = 0.654 - G

Mass of Silver = 10.5 * (0.654 -G)

Then

9.35 = 19.3 * G + 10.5 * (0.654 -G)

Solve for 'G' from above and continue....
 
Thank you for your help. Now I understand how to get the mass/volume of each of the metals. I'm still stuck on solving the equation though. Could you help me with this? My guess on what to do first was to divide 9.35/10.5, but this doesn't come out evenly. Could you help me?
 
kwikness said:
My guess on what to do first was to divide 9.35/10.5, but this doesn't come out evenly. Could you help me?
Click to expand...
What are you dividing by 9.35/10.5? Why? And why must values "come out evenly"? Were you told that all answers could be whole numbers for this particular assignment?

Please reply showing your work and providing clarification. Thank you! :D

Eliz.
 
kwikness said:
Thank you for your help. Now I understand how to get the mass/volume of each of the metals. I'm still stuck on solving the equation though. Could you help me with this?

My guess on what to do first was to divide 9.35/10.5, No

First "break open" the parenthesis (inthe right-hand-side of the equation) by distributing 10.5 over the elements inside the parenthesis.

Then collect "similar" terms and further simplify and solve.


but this doesn't come out evenly. Could you help me?
Click to expand...
 
I tried the following, but the result I get is unexpected..

9.35 = 19.3 * G + 10.5 * (0.654 -G)

9.35 = 19.3G + 6.867 - 10.5G

9.35 = 8.8G + 6.867

2.483 = 8.8G

G = .282 (rounded)

I remember from class that the percentage of gold in the jewelry was somewhere around 50%. Judging my answer from this, .282grams is not the correct answer. Did I make a mistake somewhere?

In order for this to be correct, the jewelry would have to be 9.068grams silver (total jewelry weight - weight of gold)
 
lol Niiiiiiice.. that explains alot. Thank you guys so much, you really saved my ass on this one. This forum r0xx!
 
You must log in or register to reply here.
Top