Chemistry
 

i'm having trouble remembering conversions and google is just killing me does anyone off hand remember how to switch from moles to atoms to grams and some unmber im supposed to remember something that starts with an A any help would be appreciated thank you

I think the number you're looking for is called Avogadro's Number. It is 6.02 x 10^23.

General Link

Hopefully you'll be able to figure out the conversions with this, if this is the number you need.

Basically 1 mole of something means you have as many grams as its mass number - ie 1 mole of O2 (oxygen molecule) is 32g (16x2). It also means you have 6.02 x 10^23 of them...

That site explains everything pretty well. The trickiest part of what you want to know is molar mass, which isn't too tough.

On a periodic table, each element has as small number at the bottom of its box. That's the molecular weight. If you have 1 mole of that element, then that mole will weigh the molecular weight in grams.

That means a mole of hydrogen atoms weighs about 1g. If you only have half of mole of hydrogen atoms, they'll only weigh about half a gram. Just remember that most elements aren't found in single atoms, so you have to take into account the number of atoms in each molecule, like cliche's example.

To add confusion:

The AMU number on the periodic table gives the "average" mass of 1 mole of element.

Consider that ~75% or so of Carbon in nature is "C-12" [ie. 6 protons and 6 neutrons, hence mass of ~12g/mol] however, if you look on the periodic table, Carbon has a mass of 12.011.

Why?

Because the remaining ~25% of Carbon is in the form of isotopes such as "C-13" [ie. 6 protons, 7 neutrons, which gives a mass of ~13g/mol].

The AMU given on the periodic table accounts for these isotopes.

cool thanks