Final answer:
The molecular formula of the gaseous compound that contains only sulfur and fluorine is SF4.
Step-by-step explanation:
The molecular formula of a gaseous compound that contains only sulfur and fluorine can be determined using the given information. The compound is 70.4% fluorine by mass, so the remaining percentage must be sulfur. We can assume we have 100g of the compound, which means we have 70.4g of fluorine and 29.6g of sulfur.
Next, we need to convert the mass of each element to moles. The molar mass of fluorine is 19g/mol and the molar mass of sulfur is 32g/mol. Using the molar mass, we can calculate the moles of each element. We have 70.4g of fluorine, so:
moles of fluorine = mass of fluorine / molar mass of fluorine = 70.4g / 19g/mol = 3.70 mol
We have 29.6g of sulfur, so:
moles of sulfur = mass of sulfur / molar mass of sulfur = 29.6g / 32g/mol = 0.925 mol
The ratio of sulfur to fluorine is approximately 0.25 moles of sulfur to 1 mole of fluorine. To simplify the ratio, we multiply both by 4:
sulfur:fluorine = 1:4
Therefore, the molecular formula of the compound is SF4.