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). - Chemistry

Advertisements
Advertisements
Numerical

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 mol1

Mass of benzoic acid, ws=3.9 g

Mass of benzene, W=49 g

Molar mass of benzoic acid, Ms=122 g mol1

Substituting the values, we get

`1.62 = (ixx4.9xx(3.9xx1000))/(122xx49)`

`rArri=(1.62xx122xx49)/(4.9xx3.9xx1000)`

        = 0.51

As the value of 1, benzoic acid is an associated solute.

  Is there an error in this question or solution?
2014-2015 (March) Delhi Set 1

Video TutorialsVIEW ALL [1]

RELATED QUESTIONS

Derive van’t Hoff general solution equation 


The substance ‘X’, when dissolved in solvent water gave molar mass corresponding to the molecular formula ‘X3’. The van’t Hoff factor (i) is _______.

(A) 3

(B) 0.33

(C) 1.3

(D) 1


Define van’t Hoff factor.


Calculate the amount of benzoic acid (C6H5COOH) required for preparing 250 mL of 0.15 M solution in methanol.


19.5 g of CH2FCOOH is dissolved in 500 g of water. The depression in the freezing point of water observed is 1.0°C. Calculate the van’t Hoff factor and dissociation constant of fluoroacetic acid.


Define the term Abnormal molar mass


How van’t Hoff factor is related to the degree of dissociation?


How will you convert the following in not more than two steps:

Benzoic acid to Benzaldehyde


Give reasons for the following

Elevation of the boiling point of 1 M KCl solution is nearly double than that of 1 M sugar solution.


The Van't Hoff factor (i) for a dilute aqueous solution of the strong elecrolyte barium hydroxide is (NEET) ______.


The freezing point depression constant for water is 1.86° K Kg mol-1. If 5 g Na2SO4 is dissolved in 45 g water, the depression in freezing point is 3.64°C. The Vant Hoff factor for Na2SO4 is ______.


Phenol dimerizes in benzene having van’t Hoff factor 0.54. What is the degree of association?


We have three aqueous solutions of NaCl labelled as ‘A’, ‘B’ and ‘C’ with concentrations 0.1 M, 0.01 M and 0.001 M, respectively. The value of van’t Hoff factor for these solutions will be in the order ______.


The values of Van’t Hoff factors for KCl, NaCl and K2SO4, respectively, are ______.


Van't Hoff factor I is given by expression.


What is the expected each water van't Hoff factor for and K4[F4(CN6)] when it completely dissociated in waters.


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]


When 9.45 g of ClCH2COOH is added to 500 mL of water, its freezing point drops by 0.5°C. The dissociation constant of ClCH2COOH is x × 10−3. The value of x is ______. (Rounded-off to the nearest integer)

[\[\ce{K_{f(H_2O)}}\] = 1.86 K kg 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.


Consider the reaction

\[\begin{bmatrix}\begin{array}{cc}
\phantom{.......}\ce{CH3}\\
\phantom{....}|\\
\ce{CH3CH2CH2 - \overset{⊕}{N} - CH2CH3}\\
\phantom{....}|\\
\phantom{.......}\ce{CH3}
\end{array}\end{bmatrix}\]\[\ce{OH^- ->[Heat] ?}\]

Which of the following is formed in a major amount?


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]


Why is the value of van't Hoff factor for ethanoic acid in benzene close to 0.5?


Calculate Van't Hoff factor for an aqueous solution of K3 [Fe(CN)6] if the degree of dissociation (α) is 0.852. What will be boiling point of this solution if its concentration is 1 molal? (Kb = 0.52 K kg/mol)


Share
Notifications



      Forgot password?
Use app×