Question

20. A compound of sulfur and fluorine was analyzed and found to contain 70.3% fluorine by mass. What is the empirical formula of the compound and its empirical formula mass?

Answer 1

we have mass of each elements as:
S: 29.7 g
F: 70.3 g


Divide by molar mass to get number of moles of each:
S: 29.7/32.07 = 0.9261
F: 70.3/19.0 = 3.7


Divide by smallest to get simplest whole number ratio:
S: 0.9261/0.9261 = 1
F: 3.7/0.9261 = 4

So empirical formula is:SF4

Empirical formula mass of SF4,
MM = 1*MM(S) + 4*MM(F)
= 1*32.07 + 4*19.0
= 108.07 g/mol

Answer:
SF4
108.07 g/mol