[jjkwest1]

when 4.28 g of phosphorus was burned in chlorine the product was a phosphorus chloride. Its vapor took 1.77 times as long to effuse as the same amount of CO2 under the same conditions of temperature and pressure. what is the molar mass of the phosphorus chloride?

Would you set the problem up as (x/44)^.5= 1.77   and solve for the molar mass of phosphorus chloride? i'm kind of confused because i dont know if the 4.28 g of phosphorus has anything to do with the compuatation, whether it's useless info or not.

[Borek]

You are on the right track, and 4.28 doesn't matter - at least not in question as posted.