-2
$\begingroup$

I am revisiting the concept of mole and I decided to figure out random values (for instance: mass of 1 molecule of water) to see how much I understand the concept of moles and how it relates to amu. So here is how I started:

There is 1 mole of C atoms in 12g of C and 1 C atom is 12 amu. Therefore, there is 1 mole of 1 amu in 1g. That means there are 6.02e23 nucleons in 1 gram. So, 1 nucleon is 1g/6.02e23= 1.66e-24g. A molecule of water has 14 nucleons (6 neutrons and 6 protons from oxygen and 2 protons from both H); thus, 1.66e23 x 14 should be the g of a water molecule, which turns out to be 2.33e-23. However, this is not the correct mass of water molecule (2.992 x 10¯23 grams).

Improve this question
$\endgroup$
3
  • 2
    $\begingroup$ Who said oxygen contains 6 neutrons and 6 protons? $\endgroup$
    – Ivan Neretin
    Commented Jan 31, 2018 at 7:09
  • $\begingroup$ 8............ wow. I had the valence electrons number in mind.Thanks $\endgroup$
    – Singh
    Commented Jan 31, 2018 at 7:19
  • $\begingroup$ Note that the atomic mass unit (amu) is deprecated, and instead the newer definition should be used, which is the unified atomic mass unit (u). Also note, that the molar masses of atoms and compound reflect their relative abundance, too. There are different isotopes and it is generally not true to say one carbon atom has the mass 12 u (and especially not 12 amu). $\endgroup$
    – Martin - マーチン ♦
    Commented Jan 31, 2018 at 8:20

1 Answer 1

Reset to default
4
$\begingroup$

As Ivan pointed out in the comments, I had the molar mass of water incorrect. By fixing the molar mass to 18g/mol, I get the correct answer.

Improve this answer
$\endgroup$

Not the answer you're looking for? Browse other questions tagged or ask your own question.