chemistry
posted by kiril .
You wish to increase the carbon content of a slab of steel by exposing it to a carburizing atmosphere at elevated temperature. The carbon concentration in the steel before carburization is 165.0 ppm and is initially uniform through the thickness of the steel. The atmosphere of the carburizing furnace maintains a carbon concentration of 7715.0 ppm at the surface of the steel. Calculate the time required to carburize steel so that the concentration of carbon at a depth of 61.5 x 102 cm is one half the value of the carbon concentration at the surface. The diffusion coefficient of carbon in steel is 3.091 x 107 cm2/s at the carburizing temperature. Express your answer in hours.
DATA: Error Function Values
erf(ξ < 0.6), use the approximation erf ξ = ξ
erf(1.0) = 0.84
erf(2.0) = 0.998

777.78

could you please write how you've got your numbers? I'm trying to calculate it on my own and the result is not different

I am having trouble to and BRA state this on Odesa question
Use:
concentration of carbon at a depth
___________________________________
4*(3.091*10^7)*0,26277 
it doesnt work for me, in my question i have 38.0 x 102 and when i put it into the pattern above the calculations are wrong. Could you please explain it in a simple way? why there is 4 and 0.26277 there?

DO NOT ANSWER THIS QUESTION, IT IS FOR A MIDTERM ON AN ONLINE CLASS

We know that. You're not MIT. Now kindly go away and stop spamming this site with your nonsense.

What do you gain by cheating? A little chart that says 100% but means nothing? What is the point?
Unless you are about 4 years old, you should know better. And you are spoiling it for everyone. 
Step 1:
(0.5*7715.0  7715.0)/ (165.0  7715.0)= erf(ξ)
Step 2:
erf(ξ < 0.6), use the approximation erf ξ = ξ
Step 3:
t= d^2/4*D*ξ^2
d=61.5 x 102 cm
D=3.091 x 107 cm2/s
Step 4:
t in sec > hours
Conversion seconds to hours is total/(60x60) 
I Can't get the correct answer with the above method. !!!

ξ= (0.5 * carbon concentration at the surface of the steel  carbon concentration at the surface of the steel)/ (carbon concentration in the steel before carburization  carbon concentration at the surface of the steel)