How much would the freezing point of water decrease if 4 mol of NaCl were added to 1 kg of water (Kf = 1.86°C/(mol/kg) for water and i = 2 for NaCl)?
depression in freezing point is given by formula : iKfm
m=molality=moles of solute/mass of solvent in kg = 4/1 =4 mol/kg
put in formula . WE get dT= 21.864 = 14.88
this is the required solution.
some extra knowledge. concept if i comes because u can see that NaCl breaks to Na+ and Cl- ions . This makes one mole of solute behave as two mole of it .
That is the reason the value of i=2 .( beacuse one molecule behaves as two after dissociation)