Reef Chemistry Question of the Day #55 Salinity Rise from Calcium

[Cory]

I just read this:

"Each carbon-12 atom weighs about 1.99265 × 10-23 g"

Shouldn't it be something like each carbon atom weighs .00000000000000001 grams?

 

[Randy Holmes-Farley]

I just read this:

"Each carbon-12 atom weighs about 1.99265 × 10-23 g"

Shouldn't it be something like each carbon atom weighs .00000000000000001 grams?

Each carbon 12 atom weighs exactly 12 g/Avagadros number where Avagadros number (the number of atoms in a mole) is about 6.02 x 10²³.

 

[Cory]

I'm sorry Randy I'm misunderstanding something here. It sounds like your saying each carbon atom weighs 12 grams? This can't be correct.

 

[Randy Holmes-Farley]

Twelve grams divided by Avagadros number, which is 6.02 x 10²³

So that is 1.99 x 10^-23 grams, or 0.0000000000000000000000199 grams.

 

[Cory]

Why do they use carbon 12 isotope and not hydrogen? Did avagrado just randomly pick carbon 12? Or is there something special about carbon 12 isotope?

Also after talking with my wife about moles, I understand it as a chemists word for measure, but that measure is in atoms, electrons etcetera, where a carpenters measure is in inches, feet or meters. And an electricians unit of measure is in watts, kilowatts, ohms. Something like this?

 

[Randy Holmes-Farley]

Yes, that's a reasonable explanation of moles.

I think the carbon 12 may have been arbitrary, but I'm not sure exactly why it was chosen.