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chimie · Nov 14, 2009, 07:07 AM

Question:
Result of Silicon crystal analyzation had shown that there is an amount of arsenic As atoms in silicon crystal at Concentrate percentage which is 0.0002%. Conductivity concentration which promote by heat is an eliminated amount.
Find out the electrical conducting (electrons) density?
Where Molarity of silicon = 12.1cm3/mole.
Answer:
We get N-type semiconductor
Density= w/v... (1)
V= Moles#/Molarity... (2)

1/Calculation of moles number:
Moles#=w/M.wt... (3)
= .0002*100/28.1
=7.117*10^-4 mole

2/ Calculation of volume:
back to equation #2
V=7.117*10^-4/12.1
=5.88*10-5 cm3

3/W of Si =moles#/atomic mass
= 7.117*10^-4/28.086
= 2.534*10^-5gm

Back to density
D = 2.534*10^-5/5.88*10^-5
= 0.4309 gm/cm3

Question: where could the previous answer take me to?

Information:
I'm already known that it's N-type SC which means the electrical conductive is electron.
Question:
Did I need to find the electron numbers?

I had another idea about molar mass could answer the problem

I need to draw the valance and conductive band.

Unknown008 · Nov 14, 2009, 08:21 AM

Just got your PM. Sorry, I don't know about conductance :(

I'm not even sure what w and v means in your first formula :o

chimie · Nov 14, 2009, 08:38 AM

I meant Molarity and weight. Where could I have an answer for the previous question. My professor award two mark to solve this problem. I need it tomorrow.
I love you Jerry
Thanks anyway

Unknown008 · Nov 14, 2009, 08:46 AM

Well, if I knew some of the theory behind it... :o

I don't even understand how you can calculate the amount of moles when you don't know the size or weight of the material.

For 1, you used the percentage for As, and used atomic mass of Si? :confused:

chimie · Nov 14, 2009, 08:53 AM

I don't know this is how it set in my mind. And I'm sure about moles calculus. It could be why not?

chimie · Nov 14, 2009, 09:02 AM

Jerry where can I go for an answer?
I tried Brainemass, tutorvista but with no benefit. If you can help me to find professional help, I'll be so glad.

Unknown008 · Nov 14, 2009, 09:10 AM

Sorry, I don't know any site :(

I can try with my teacher, but he's not yet a fast typer, he hates to say it, but he takes more than an hour to type a single short paragraph...

chimie · Nov 14, 2009, 09:15 AM

Merci Infiniment !

Unknown008 · Nov 14, 2009, 09:21 AM

De rien :)

Malgre le fait que je n'ai pas vraiment repondu a ta question :o

chimie · Nov 17, 2009, 08:31 AM

Hello Jerry,
Guess what?
I have the answer
12.1 cm of the power 3…….. 6.02*10of the power 23
1 cm of the power 3 ……… ?

= 6.02*10 of the power 23/ 12.1 = 4.98* 10 of the power 22 cm of the power 3
AS atoms in one cm of the power 3 :
4.98* 10 of the power 22 * 0.0002/100 = 9.95 * 10 of the power -16 As atoms/cm of the power 3

Electrons number's 9.95 * 10 of the power -16 electrons since it's N-Type semiconductor.
Ce n'est pas la mer à boire
Easy huh! But why it's not reveal right away?
Thank You Jerry.

Unknown008 · Nov 17, 2009, 08:39 AM

Hmm, but why is the question 'the number of moles'? It should have been the number of atoms, don't you think so? :rolleyes:

Well, I'm happy to know that it was easy after all. Do you have the other answers too?

chimie · Nov 17, 2009, 09:29 AM

No Thanks
I'll go out for dinner would you join me Monsieur?

Unknown008 · Nov 17, 2009, 09:32 AM

Lol! Si vous insistez! :cool:

chimie · Nov 17, 2009, 09:36 AM

Oui,I'm.

chimie · Nov 17, 2009, 09:44 AM

Wish me luck!
Au revoir!

Unknown008 · Nov 17, 2009, 09:45 AM

Good Luck! A bientot!