Question

if any solute A dimersies at water 1 atm pressure nd boiling pointof this solution is 100.52celsius.If two moles of A is added to 1 kg of water is 0.52 celsius/ molal. calculate the % association of A

Answer 1

hii ,

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Formula for calculating i (vant haff factor) using given data is :
ΔT = i Kb m .....(1)
ΔT = elevation in boiling point = observed boiling point-original boiling point

     = 100.52° C - 100° C​
      = 0.52° C​
Kb = 0.52° C​ kg mol-1

m = moles of solute in per kg of solvent = 2 mol kg-1

Putting the values in given equation (1)

i = ∆T/Kb× m

 =0.52° / C0.52°C kg mol-1× 2 mol kg-1

=0.5
 
 Let α be the degree of association.

At equilibrium the concentration of A would be 1-α

Concentration of dimerised form will be α/2 mole

Total number of moles in solution =  1-α + α/2
                                          = 1-α/2

i = total moles in solution
0.5 = 1-α/2
α/2= 1/0.5
α = 1
It indicates that percentage of association of A is 100 %


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Hope it helps u :))

# Nikky



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