A helium balloon contains 0.26 g of helium. How many moles of helium does it contain?

...........1 mole

0.26g He * ------- = 0.065 moles He
...........4.0026g

(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 = ??

To find the number of moles of helium in the balloon, you need to use the molar mass of helium. The molar mass of helium is approximately 4.0026 g/mol.

To calculate the number of moles, you can use the formula:

Number of moles = Mass of substance (in grams) / Molar mass

Plugging in the values:

Number of moles = 0.26 g / 4.0026 g/mol

Number of moles ≈ 0.065 moles

Therefore, the helium balloon contains approximately 0.065 moles of helium.