Question

Calculate the KCl to be dissolved in 1 kg water. So that freezing point is dipresaed by 2 kelvin. Kf for water is 1/86 k /kg/mol

Answer 1

Here we used freezing point depression formula.
where,
wA = 1000g (given)
Kf=1.86 kf/mole (given)
delta Tf = 2k
Mb for KCl = 39.09+5.45 =75.54 per mol

So, Wb comes out to br  80.15 g

see attached image for calculation part

Answer 2

Heya..

Here is your answer...

Dear student!

We know that depression in freezing point,

ΔTf = Kf x m

Where m = molality i.e no. of moles of solute dissolved in per Kg solvent.

Here ,m = ΔTf /Kf =  2/1.86 = 1.07 

We know that molality of KCl (m) = no. of moles of KCl /solvent in Kg.

So, for 1 Kg of water, no . of moles of KCl = 1.07 x 1= 1.07 moles.

Hence, 1.07 moles of KCl is dissolved in the solution.

It may help you ....☺☺