October 6, 2015

Homework Help: College Chemistry/Lab Math

Posted by James on Sunday, March 17, 2013 at 1:46pm.

I think I have this problem figured out correctly, but is there anyone who can tell me if I'm doing something wrong.

The question is...

"One troy ounce of gold is worth $380. There are 33.8 grams per troy ounce. You have a stock colloidal solution of a very fine gold dust. It's concentration is .10% w/v. From this solution 1.0 ml is placed in 9.0 ml of an isotonic, pH buffered solution to make a working stock. An assay calls for .50 ml of this working stock to which is added .10 ml of serum. What is the cost of gold used for each test?

My work:

.10 % w/v gold = .10 g gold (in 1 ml)

(.10 g gold)/(1 ml + 9 ml) = .01% w/v gold (or .01 g gold)

(.01 g gold)/(1 ml) x (5 ml)/(1) = .005 g gold in final solution

.005 g gold x (1 troy ounce)/(33.8 g gold) = .0001479 troy ounces of gold in the final solution

.0001479 x $380 = about $.06 per test

Any guidance would be greatly appreciated. Thanks!

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