Question

how to find vant hoff factor loke for ex of NaCl CaCl2... plz reply

Answer 1

★Vant Hoff factor is the ratio of observed colligative properties and normal colligative properties.
★It is represented by (i).

# There are two cases to find vant Hoff factor

1) Dissociation
2) Association

Case #01--› Dissociation

AxBy ------> xA^+y + yB^+x

Initial moles of reactant = 1 and that of product = 0
After a time't',
Reactant = 1 - ß and of products for first it is xß and for second it is xß

Total mole after Dissociation = 1 - ß + xß + yß
= 1 - ß(x + y - 1)...........(1)

Here x and y are stoichiometry coefficient and ß represents Dissociation coefficient.

x + y = Stoichiometry mole of the product [N]

Total mole after Dissociation = 1 - ß(N - 1)........ from (1)

And since,
i = Observed colligative properties/Normal colligative properties

So, i = 1 + ß(N - 1)/1
i = 1 + ß(N - 1)

ß =( i - 1) / (N - 1)

If ß = 100℅

i = 1 + ß(N - 1)
i = 1 + N - 1
i = N

Now example ---›
NaCl --› Na^+ + Cl^-

So, N = 2

CaCl2 --› Ca^+ + 2Cl

So, N = 3

Case #02---› Association
nA ---› (A)n
Initial moles of reactant = 1 and that of product = 0

After time 't' --> Moles of reactant = 1 - nx and that of the product = x

[nx = aß
here n = stoichiometry coefficient
a = initial moles = 1
x = ß/n]

So, moles of reactant = 1 - ß and that of the product = ß/n

Total moles after Association = 1 - ß + ß/n
= 1 + ß(1/n - 1)

here n = stoichiometry coefficient of reactant

i = 1 + ß(1/n - 1)/1

ß = i - 1/(1/n)-1

If ß = 100℅
i = 1/n

Example --›

2A ----› (A)2 .......(Dimer)
here i = 1/2

3A ----› (A)3........( Trimer)
here i = 1/3

Thank you
#shati
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