Verified Solution • 2025–26 Session moderate

QJEEM07Chca23: JEE Main 2007 Chemistry - Class 12 JEEM07Chca23 Solution: A 5.25 % solution of a substance is isotonic with a 1.5%…

A 5.25 % solution of a substance is isotonic with a 1.5% solution of urea (molar mass = 60 g mol−1) in the same solvent. If the densities of both the solutions are assumed to be equal to 1.0 g cm−3, molar mass of the substance will be

Multiple Choice Options

  • A 90.0 g mol−1
  • B 115.0 g mol−1
  • C 105.0 g mol−1
  • D 210.0 g mol−1

Step-by-Step Verified Solution

TIPS/FORMULAE:

Osmotic pressure (π)\left( \pi \right) of isotonic solutions are equal.

For solution of unknown substance (π=CRT)\left( {\pi = CRT} \right)

C1=5.25/MV{C_1} = {{5.25/M} \over V}

For solution of urea,

C2  C{}_2\,\, (concentration) =1.5/60V= {{1.5/60} \over V}

Given, π1=π2{\pi _1} = {\pi _2}

as     π=CRT\,\,\,\,\pi = CRT

∴\therefore      C1RT=C2RT  \,\,\,\,\,{C_1}RT = {C_2}RT\,\, or   C1=C2\,\,{C_1} = {C_2}

or     5.25/MV=1.8/60V\,\,\,\,{{5.25/M} \over V} = {{1.8/60} \over V}

∴\therefore      M=210g/mol\,\,\,\,\,M = 210g/mol

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