posted by pip .
A helium balloon contains 0.26 g of helium. How many moles of helium does it contain?
0.26g He * ------- = 0.065 moles He
(you divide how many grams you have by the atomic mass [which is the # below the element symbol on the periodic table])
(Sorry about the spacing, the formatting gets messed up when you post a message)
Yes, spacing is a problem. We work around it by doing it this way.
# mols = g/molar mass.
# mols = 0.26/4.00 = ??