Question

Elemental sulfur occurs as octatomie molecules, `S_8`. What mass of fluorine gas is needed to react completely with 28.6 g of sulfur to form sulfar hexafluoride?

Answer 1

Approx. `100*g`.

Explanation:

We need (i) a stoichiometric equation:

`S(s) + 3F_2(g) rarr SF_6(g)`.

And (ii) the molar equivalence of sulfur and fluorine `=`

`(28.6*g)/(32.06*g*mol^-1)` `=` `0.892*mol`.

And thus `0.892xx3xx38.00*g*mol^-1` `~=` `100*g` fluorine gas are required.

Just a note on the molecularity of sulfur, of course I could have treated it as `S_8` as you did. The arithmetic is a bit easier if I give the equation as written above: 3 equiv of fluorine gas react with 1 equiv of sulfur. Note that fluorine, like all the other elemental gases (SAVE FOR THE NOBLE GASES), is binuclear, i.e. a diatomic molecule.