Question

Determine the empirical formula for a compound that is found to contain 10.15 mg P and 34.85 mg Cl.?

So I got the answer by dividing

10.15 mg P / 30 g P = .328

.328 / .328 = 1

34. mg Cl / 35.453 g Cl = .983 Cl

.983 Cl / .328 =3
PCl3

But I'm confused because I thought I had to convert 10.15 mg to grams but then I get a huge number if I do that. Why do I leave it as mg?

Answer 1

if you get a large number converting mg to g, then you're moving the decimal in the wrong direction. 10.15mg is 0.01015g. Then convert to moles