LIVE Course for free

Rated by 1 million+ students
Get app now
0 votes
in Solutions by (47.9k points)
closed by

How would you determine molar mass from relative lowering of vapour pressure.

1 Answer

+1 vote
by (46.8k points)
selected by
Best answer

1. The measurement of relative lowering of vapour pressure can be used to determine the molar mass of a non-volatile solute. 

2. A known mass of the solute is dissolved in a known quantity of solvent. The relative lowering of vapour pressure is measured experimentally. 

3. According to Raoult’s law, the relative lowering of vapour pressure is

WA = weight of solvent 

WB = weight of solute 

MA = Molar mass of solvent 

MB = molar mass of solute

where, nA = number of moles of solvent 

nB = number of moles of solute.

For dilute solution, nA > > nB , nA + nB = nA

Then,  \(x_B=\frac{n_B}{n_A}\)

Number of moles of solvent and solute arc

From the above equation, molar mass of the solute MB can be calculated using the known values of WA , WB , MA and the measured relative lowering of vapour pressure.

Welcome to Sarthaks eConnect: A unique platform where students can interact with teachers/experts/students to get solutions to their queries. Students (upto class 10+2) preparing for All Government Exams, CBSE Board Exam, ICSE Board Exam, State Board Exam, JEE (Mains+Advance) and NEET can ask questions from any subject and get quick answers by subject teachers/ experts/mentors/students.