Question

benzene at a certain temperature is 0.850bar. A non- ute solid weighing 0.5 g when added to 39.0 g of benzene 1.). Vapor pressure of the solution, then, is 0.845 bar. 4. The vapor pressure of pure benzene at a volatile, non-electrolyte solid weigh (molar mass 78 g mol-1). Vapor press (0) What is the molar mass of the solid substan 39g + 5g= 39.5 g pwm = ,ASU bar

Answer 1

from Rould's law of relative lowering of vapour pressure we know that when a non volatile solute is added to a sowent its vapour pressure i decreased and relative lowering of vapour pressure is equal to the mole fraction of solute. so - where PA = Vapour pressure of sowent NB I PA = Vapour pressure of solution Xo = Mole fraction of solure 7 Putting the values 0 0.850 bar -0.845 bar. bar. X8 0.850 bar 0.050 Oreille 0.8 so Ete = 1246 +1x62 789fra? We know Moles of soute Total moles 0.5g/Msonte weight of soluta 0.059 -- Msolute = Molecular oosg + 39.0g Msowe 78.09mo nostroisg = o.sg ro.059 +0.059 x 340g Isolute solute Msonte wat d a te 78.0g/mol 0.(1-0.059) = 0.0295 mol - Msowe 0:50 x 0.941 g/mol 7 . Msolute = 0.0295 =) Msoewe = 15.95 g/mol. which is the required molar mass of solute