An aqueous solution of 2% non-volatile solute exerts a pressure of 1.004 bar at the normal boiling point of the solvent. What is the molar mass of the solute?
Answers
Molar Mass: It is defined as the mass of a given chemical element or chemical compound in gram, divided by the amount of substance (mol).
The molar mass of a compound can be calculated by asthmatically adding the standard atomic masses of the individual elements present in the compound(in g/mol) of the constituent atoms.
Calculation: Here,Vapour pressure of the solution at normal boiling point (p1) = 1.004 bar (Given).
Vapour pressure of pure water at normal boiling point (p10) = 1.013 barMass of solute, (w2) = 2 g.
Mass of solvent (water), (w1) = 100 - 2 = 98 g.
Molar mass of solvent (water), (M1) = 18 g mol – 1.
According to Raoult's law,:(p10 - p1) / p10 = (w2 x M1 ) / (M2 x w1 ):(1.013 - 1.004) / 1.013 = (2 x 18) / (M2 x 98 ):0.009 / 1.013 = (2 x 18) / (M2 x 98 ):M2 = (2 x 18 x 1.013) / (0.009 x 98):M2 = 41.35 g mol – 1.
Hence, the molar mass of the solute is 41.35 g mol - 1.