Chemistry people....come here

[ViEtGuRL]

Help??? I can't find this answer ANYWHERE!!!

Why does the specific amount of 12 g of 12C (carbon-12) selected as the basis for defining 1 mole? (Why not 13g, for example? Did some law of nature require this exact mass? Or was it picked for convenience? if so, why is 12 g convenient?)

 

[n7of9]

cause 12 is a much nicer number..just look at the 2 numbers next to eachother and you will see that 13 starts to get annoying after a while, but 12 just keeps shining on [ i've actually got no idea of what you are talking about OR or what i'm talking about ]

 

[ViEtGuRL]

stochiometry

 

[syd]

I'm not 100% sure what you mean as I haven't done any chem in over 2 years.

But I hope this can help somehow:

http://www.ausetute.com.au/moledefs.html

"1 mole contains the same number of particles as there are in 12g of carbon-12 atoms by definition.
This number is called Avogadro's number or Avogadro's constant (NA) and is equal to 6.022 x 1023 particles. "

 

[Wojtek]

Originally posted by ViEtGuRL
Help??? I can't find this answer ANYWHERE!!!

Why does the specific amount of 12 g of 12C (carbon-12) selected as the basis for defining 1 mole? (Why not 13g, for example? Did some law of nature require this exact mass? Or was it picked for convenience? if so, why is 12 g convenient?)

Humm,

I don't know, but I guessed something is mixed up now.

1 mol = 1 mol of a given substance, 1 mol DOES NOT equal 12g.

Lets say you got this NaCl.
Atomic weight of Na = 22.99
Atomic weight of Cl = 35.45
Total weight = 22.99+35.45=58.44
1 mol of NaCl = 58.44g

Now if you have to lets say calculate the number of moles in 500g of NaCl, you do 500/58.44 and you get 8.56.

That's how do you do.


Now, as for the Cobalt12 thing, let me explain.

To construct the periodic table of elements, Mandeliev weighted all substances and wrote their weights. He then choosed the lighest one (Hydrogen, H) and created a 'symbolical' weight.

Ex: Hydrogen is 1.01 and Calcium is 40.07. This means Calcium is 40.07 times heavier then Hydrogen. During history of Chemistry, 3 elements were used to compare. Hydrogen, Oxygen and now Cobalt12.

Why Cobalt12? Simply because it's atomical structure if the most stable of all elements.


I hope this answers your question




Btw, n7of9, stopp skipping school :biggrin2:

 

[Gayowulf]

carbon 12 is the most common and most stable isotope of carbon. It also happens to be exactly 12x as massive as Hydrogen. It's the only isotope of any element to add up so nicely. That's why it's used thus the governing bodies of checmistry chose to measure all things based on carbon.

1 mol really has nothing to do with mass; its all about atoms. 1 mol of carbon contans 6.022x10^23 atoms and 1 mol of bannans contains 6.022^23 bananas.

avogadro's number is also the amount of molecules in 1 cc of a gas.