Advertisements
Advertisements
Question
3.9 g of benzoic acid dissolved in 49 g of benzene shows a depression in freezing point of 1.62 K. Calculate the van't Hoff factor and predict the nature of solute (associated or dissociated).
(Given : Molar mass of benzoic acid = 122 g mol−1, Kf for benzene = 4.9 K kg mol−1)
Advertisements
Solution
We know that the depression in freezing point is given by
`DeltaT_`
Here,
van't Hoff factor = i
Depression in freezing point, ΔTf=1.62 K
Kf for benzene=4.9 K kg mol−1
Mass of benzoic acid, ws=3.9 g
Mass of benzene, W=49 g
Molar mass of benzoic acid, Ms=122 g mol−1
Substituting the values, we get
`1.62 = (ixx4.9xx(3.9xx1000))/(122xx49)`
`rArri=(1.62xx122xx49)/(4.9xx3.9xx1000)`
= 0.51
As the value of i < 1, benzoic acid is an associated solute.
APPEARS IN
RELATED QUESTIONS
Calculate the amount of benzoic acid (C6H5COOH) required for preparing 250 mL of 0.15 M solution in methanol.
How van’t Hoff factor is related to the degree of dissociation?
The van’t Hoff factor (i) accounts for ____________.
Van’t Hoff factor i is given by the expression:
(i) i = `"Normal molar mass"/"Abnormal molar mass"`
(ii) i = `"Abnormal molar mass"/"Normal molar mass"`
(iii) i = `"Observed colligative property"/"Calculated colligative property"`
(iv) i = `"Calculated colligative property"/"Observed colligative property"`
Maximum lowering of vapour pressure is observed in the case of ______.
Geraniol, a volatile organic compound, is a component of rose oil. The density of the vapour is 0.46 g L–1 at 257°C and 100 mm Hg. The molar mass of geraniol is ______ g mol–1. (Nearest Integer)
[Given: R = 0.082 L atm K–1 mol–1]
A storage battery contains a solution of H2SO4 38% by weight. At this concentration, Van't Hoff Factor is 2.50. At the battery content freeze temperature will be ______ K.
(Kf = 1.86 K Kg mol−1)
The degree of dissociation of Ca(NO3)2 in a dilute aqueous solution containing 7 g of the salt per 100 g of water at 100°C is 70%. If the vapour pressure of water at 100°C is 760 mm. The vapour pressure of the solution is ______ mm.
A molecule M associates in a given solvent according to the equation \[\ce{M <=> (M)_n}\]. For a certain concentration of M, the van't Hoff factor was found to be 0.9 and the fraction of associated molecules was 0.2. The value of n is ______.
When 19.5 g of F – CH2 – COOH (Molar mass = 78 g mol−1), is dissolved in 500 g of water, the depression in freezing point is observed to be 1°C. Calculate the degree of dissociation of F – CH2 – COOH.
[Given: Kf for water = 1.86 K kg mol−1]
