textbook F13

[Nan_Guan_1L]

In an experiment, 4.14 g of phosphorus combined with chlorine to produce 27.8 g of a white solid compound. (a) What is the empirical formula of the compound? (b) Assuming that the empirical and molecular formulas of the compound are the same, what is its name?

I had trouble getting the right answer for a, which is PCl5.
Instead I got P2Cl5 by doing the following:
moles of P: 4.14/30.973=0.1333
moles of Cl: (27.8-4.14) / 35.5x2 = 0.333
0.333/0.1333=2.5 --> and that's how I got P2Cl5.
I figured the textbook did 35.5 for molar mass of chlorine instead of 35.5x2. I though chlorine is Cl2. can somebody tell me where I did wrong or is this an error in the textbook. thank you!!

[Lindsey_Su_3A]

Chlorine is only diatomic (Cl2) when it is standing alone, like O2. So for the molar mass, you would just use 35.5.

Hope that helps!

[Natalie Do 3F]

First you devide 4.14 g by the molar mass to get .134 moles. You then find the moles of Cl by subtracting 4.14 from 27.8 and dividing by the molar mass to get .667. Divide both by the smaller (.134) to get the ratio 5:1