Posted by **Jasmine** on Friday, October 20, 2006 at 3:08pm.

calculate the molar mass ofthe substance. divide it by Avogadros number (6.02x10 to 23 power)

.)Hydrogen2

2/(6.02 x 10^23) = ??

hun i don't get it the teacher said first H2x1.00 and then (6.02xio^23) but i still don't get it can you help?

I assume you don't understand where the number two comes from and why 6.02 x 10^23 is used. Look on the periodic table and see that the element H has an atomic mass of 1.0, if we round to the nearest tenth. A mole of hydrogen atoms will weigh 1.0 grams. Hydrogen is a gas and normally occurs as the diatomic molecule, meaning that there are two hydrogen atoms, H2, in one molecule. So the molar mass is 2 x 1.0 = 2.0 g per mole as opposed to the atomic mass of 1.0 g per mole. There are 6.02 x 10^23 molecules in a mol of H2 molecules; therefore, the 2.0 grams represents 6.02 x 10^23 molecules. I assume your teacher is dividing 2.0g/6.02 x 10^23 molecules/mole = 3.32 x 10^-24 g for the mass of 1 molecule of hydrogen. The mass of 1 atom of H would be just 1/2 that or 1.66 x 10^-24 g. I hope this helps.

thanks it helps.

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