Really confused about this one?

Question

I always thought that 1 mole of anything = 6.02x10^23 particles (whether they be atoms, ions etc.) until today. A question came up in class which said 'How many atoms in 1 mole of Fe2O3?' I figured it would just be 6.02x10^23 but apparently I was wrong: the teacher said it was 1.02x10^24 or something like that. Am I wrong? Also, how do I figure out the avergae weight (in kg) of 1 atom of hydrogen?

Answer 1

A mol is a mol is a mole.  The question asks the # of atoms in a mol of Fe2O3 (molecules!).  There are 6.02 x 10^23 molecules in one mol of this and since there are 5 atoms per mol you just need to mulitply avagoadros # by 5.

1 atom of H?  The molar mass of H is 1.008 g/mol.  So to get the average wt in Kg you would use

1.008 g/mol  * 1mol/6.02 x 10^23 *1kg/1000g = 1.674 x 10 ^-27 kg

Answer 2

ok. in 1 mole of Fe2O3, there are basically 5 atoms (2 iron and 3 oxygen) so, you need to take 6.02x10^23 x 5 to get the correct answer3.01x10^23.

If the answer is 1.02x10^24, then perhaps the full question was how many atoms of iron? then it would be 6.02x10^23 x 2 to get 1.02x10^24.

next part,

1 atom of hydrogen = 1/6.02x10^23 moles of hydrogen.

so, the relative atomic mass of hydrogen is 1

mass=moles x atomic mass

therefore, the mass would be 1.66x10^-27kg