34 . 05 mL of phosphorus vapours weigh 0.0625 g at `546 .^(@)C` and 0.1 bar pressure . What is the molart mass of phosphorus ?

Explanation

According to gas equation,
`PV = nRT`
or `PV =w/M RT`
Given : `P = 0.1 " bar," V = 340.5 mL = 340.5 xx 10^(-3) dm^3, W = 0.0625 g, R = 0.0831 " bar " dm^3 K^(-1) mol^(-1)`
`T = 546^@C = 819 K, M` = ?
`:. M=(W.R.T)/(P.V)= (0.0625 xx0.0831 xx 819)/(0.1 xx 340.5 xx 10^(-3))`
= `124.92 g mol^(-1)`
Hence, molar mass of phosphorus is `124.92 g mol^(-1)`.