College Chemistry/Lab Math
posted by James
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!

James
Sorry, in my 3rd step it should be "(.5ml)/(1)"

Devron
This is good, but mass/volume %= (g/mL)*100
So,
(0.10 % w/v)/100 = 0.001 g gold (in 1 ml)
And so,
(0.001g gold)/(1 ml + 9 ml) = 0.0001g of gold/mL
****Don't worry about mass/volume % at this point.
But now you have a solution that is 0.0001g of gold/mL
You remove 0.5mL of solution and add it to 0.10 mL of serum.
How much gold is in a total volume of 0.60 mL?
0.0001g of gold/mL *(0.10mL)=0.00001g of gold
Your new concentration will be
0.00001g of gold/total volume=0.00001g of gold/0.60mL=1.67 x 10^5 g of gold/mL
or 1.67 x 10^5 g of gold/mL*(100)=1.67 x 10^3 % m/v
So, each test uses 0.00001g of gold
0.00001g of gold*(1 troy ounce)/(33.8 g gold) = 2.96 x 10^7 troy ounces of gold in the final solution
(2.96 x 10^7)* ($380/oz) = $1.12 x 10^4
The test isn't that expensive. 
James
Why did you multiply 0.0001g of gold/mL by 0.10mL? Shouldnt it be .50 mL? I say this because .10 is the volume of serum added, which does not contribute to the total amount of gold in the final solution.

Devron
Thank you for catching that.
0.0001g of gold/mL *(0.50mL)=0.00005g of gold
Your new concentration will be
0.00005g of gold/total volume=0.00005g of gold/0.60mL=8.33 x 10^5 g of gold/mL
or 8.33 x 10^5 g of gold/mL*(100)=8.33 x 10^3 % m/v
So, each test uses 0.00005g of gold
0.00005g of gold*(1 troy ounce)/(33.8 g gold) = 1.48 x 10^5 troy ounces of gold in the final solution
(1.48 x 10^5)* ($380/oz) = $5.62 x 10^3 
James
Thanks for the help!

Kip
go back to basics and CHECK YOUR NUMBERS. There are only 31.1 grams in a troy ounce my friend...
Respond to this Question
Similar Questions

Physics
At the time this problem was written, the price of gold was $427 per ounce, while that of platinum was $866 an ounce. The "ounce" in this case is the troy ounce, which is equal to 31.1035 g. The density of gold is 19.3 g/cm^3 and that … 
Chemistry
I am trying to figure out how much 1.134 grams worth of gold will cost, if gold is at 380 dollars an ounce. I set up proportions like this: 380 doll./1.34 grams (how many grams are in an ounce) = BLANK/1.134 grams (mass of coins). … 
Distribution & probabilities
Fluctuation in the prices of precious metals such as gold have been empirically shown to be well approximated by a normal distribution when observed over short interval of time. In May 1995, the daily price of gold (1 troy ounce) was … 
MAT201
Fluctuation in the prices of precious metals such as gold have been empirically shown to be well approximated by a normal distribution when observed over short interval of time. In May 1995, the daily price of gold (1 troy ounce) was … 
Chem
The price of gold is $625 per troy ounce at this writing. How much heat (in J) is needed to raise the temperature of $5000.00 worth of gold from 29.5 oC to 70.5 oC? 
chemistry
platinum metal currently costs $1700 per troy ounce ( note: this is different than a regular ounce 1 troy ounce =31.1035 g. what would the costs be, in dollars , to purchase enough platinum to form a solid cone with maximum radius … 
chemistry
Rhodium metal currently costs $1251. per troy ounce (note this is different than a regular ounce! 1 troy ounce = 31.1035g). What would the cost be in dollars to purchase enough gold to form a solid square based pyramid with base dimensions … 
pre calc
A jeweler wants to make a 1 ounce ring composed of gold and silver, using $200 worth of metal. If gold costs $6000 per ounce and silver is $50 per ounce, how much of eat metal should she use? 
Science
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. Its concentration is .1% w/v. from this solution, 1 ml is placed in 9 ml of an isotonic, pH buffered … 
chemistry
A coin dealer offers to sell you an ancient nickel coin that is 3.1 cm in diameter and 4.65 mm in thickness. A) The density of nickel is 8.9 g/cm3. How much should the coin weigh if it is pure nickel?