Question

How many moles of molecules are in 40g of H2O?

Answer 1

40/18 moles,since one mole of water weighs 18 grams.

Answer 2

thanks

Answer 3

:)

Answer 4

that is a bit over 2 times Avogadro's number of molecules

Answer 5

40g / 18 =2.22 gmole H2O

Answer 6

@ScottWu
That should be
\[\frac{40~(g~H_2O)}{18~(g~H_2O/mol)}=2.2~mol \]
the unit of mass has cancled out

Answer 7

Oh, but i think the gmole means the dimension depends on grams.
Take water for instance, we say the molecular weight is 18 and the unit can be g mol, lb mol, kg mol ...etc.
The molecular weight is dimensionless in some sense.
Am I right? (Maybe we should ask our prof. for check.)

Answer 8

we say the molecular weight is 18 grams per mole