Physical Chemistry

relation between molarity and molality

rak

12 Years agoGrade

2 Answers

bharat bajaj

12 Years ago

Molarity/Molality = (moles of solute/volume of solution) × (mass of solvent/moles of solute)
           = mass of solvent (in kg)/volume of solution (in litre)
           = mass of solvent (in grams)/volume of solution = W/V  
Let the density of the solution be d.   Unit= g mL−1 
Mass of solution = V × d 
Mass of solute = number of moles × molecular mass of solute 
          = n mA
Mass of solvent, W = mass of solution – mass of solute 
          = V × d – n × mA 
Thus,  Molaity/Molality (M/m) = V×d–n×mA/V
  Molaity (m) = molarity×V/V×d–n×mA 
                    =molaity/d–n/V×mA 
                  m =molaity/d–molaity×mA 
where wZ, wBare masses of solvent and solute respectively xAand xBare mole fractions of solvent and solute respectively mAis molecular mass of solvent.

Thanks
Bharat Bajaj
Askiitians faculty

Arun Kumar

12 Years ago

$\\m={n \over W}={ M \over {1000d-M*M_o \over 1000}}={1000M \over {1000d-M*M_o}} \\$where m is molality$ \\$M is no. of moles$ \\$M_o is the molecular mass$ \\$d is density in g/cc$$