Solutions

JEE Chemistry · 84 questions · Page 9 of 9 · Click an option or "Show Solution" to reveal answer

Q81
Which of the following binary mixture does not show the behaviour of minimum boiling azeotropes?
A CH3OH+CHCl3\text{CH}_3\text{OH} + \text{CHCl}_3
B C6H5OH+C6H5NH2\text{C}_6\text{H}_5\text{OH} + \text{C}_6\text{H}_5\text{NH}_2
C H2O+CH3COC2H5\text{H}_2\text{O} + \text{CH}_3\text{COC}_2\text{H}_5
D CS2+CH3COCH3\text{CS}_2 + \text{CH}_3\text{COCH}_3
Correct Answer
Option B
Solution

A binary mixture of C6H5OH \text{C}_6\text{H}_5\text{OH} and C6H5NH2 \text{C}_6\text{H}_5\text{NH}_2 exhibits negative deviation from Raoult's law.

This means that the vapor pressure of the solution is lower than the vapor pressures of the pure components, C6H5OH \text{C}_6\text{H}_5\text{OH} and C6H5NH2 \text{C}_6\text{H}_5\text{NH}_2 .

Consequently, the boiling point of the solution is higher than the boiling points of the pure substances.

Therefore, this mixture forms a maximum boiling azeotrope.

Q82
We have three aqueous solutions of NaCl\mathrm{NaCl} labelled as ' A\mathrm{A} ', ' B\mathrm{B} ' and ' C\mathrm{C} ' with concentration 0.1M0.1 \mathrm{M}, 0.01M0.01 \mathrm{M} and 0.001M0.001 \mathrm{M}, respectively. The value of van 't Hoff factor(i) for these solutions will be in the order :
A iA<iC<iB\mathrm{i}_{\mathrm{A}}<\mathrm{i}_{\mathrm{C}}<\mathrm{i}_{\mathrm{B}}
B iA<iB<iC\mathrm{i}_{\mathrm{A}}<\mathrm{i}_{\mathrm{B}}<\mathrm{i}_{\mathrm{C}}
C iA>iB>iC\mathrm{i}_{\mathrm{A}}>\mathrm{i}_{\mathrm{B}}>\mathrm{i}_{\mathrm{C}}
D iA=iB=iC\mathrm{i}_{\mathrm{A}}=\mathrm{i}_{\mathrm{B}}=\mathrm{i}_{\mathrm{C}}
Correct Answer
Option B
Solution

th, .header { background-color: #0000FF; color: white; } Salt Values of i (for different conc. of a Salt) NaCl 0.1 M 0.01 M 0.001 M 1.87 1.94 1.94 The van 't Hoff factor (i) is used to describe the number of particles a solute formula unit produces in a solution.

For an electrolyte like NaCl\mathrm{NaCl}, which dissociates completely in very dilute solutions, the theoretical value of ii is approximately 2, since NaCl\mathrm{NaCl} dissociates into Na+\mathrm{Na}^+ and Cl\mathrm{Cl}^- ions.In real scenarios, as the concentration of the solution decreases (making the solution more dilute), the interaction between the ions decreases, allowing more complete dissociation.

Therefore, for practical purposes, the van 't Hoff factor ii approaches its theoretical maximum value as concentration decreases.

Thus, for NaCl\mathrm{NaCl} solutions of concentrations 0.1M0.1 \mathrm{M}, 0.01M0.01 \mathrm{M}, and 0.001M0.001 \mathrm{M}, the fact that NaCl\mathrm{NaCl} dissociates more completely in more dilute solutions implies that ii increases with decreasing concentration.Hence, the order of ii based on the concentration would be iA0.01M>0.001M\mathrm{i}_{\mathrm{A}} 0.01 \mathrm{M} > 0.001 \mathrm{M}, respectively.

Thus, option B correctly describes the order of the van 't Hoff factors for these solutions.

Q83
A solution is made by mixing one mole of volatile liquid AA with 3 moles of volatile liquid BB. The vapour pressure of pure A is 200 mm Hg and that of the solution is 500 mm Hg . The vapour pressure of pure B and the least volatile component of the solution, respectively, are:
A 1400 mm Hg,A1400 \mathrm{~mm} \mathrm{~Hg}, \mathrm{A}
B 1400 mm Hg,B1400 \mathrm{~mm} \mathrm{~Hg}, B
C 600 mm Hg,A600 \mathrm{~mm} \mathrm{~Hg}, \mathrm{A}
D 600 mm Hg,B600 \mathrm{~mm} \mathrm{~Hg}, \mathrm{B}
Correct Answer
Option C
Solution

Given: 1 mole of volatile liquid A 3 moles of volatile liquid B Vapor pressure of pure A, PAo=200 P_A^o = 200 mm Hg Vapor pressure of the solution, PS=500 P_{S} = 500 mm Hg We apply Raoult's law, which states: PS=PAoXA+PBoXB P_{S} = P_A^o \cdot X_A + P_B^o \cdot X_B Where: XA X_A is the mole fraction of A XB X_B is the mole fraction of B PBo P_B^o is the vapor pressure of pure liquid B Calculate the mole fractions: XA=11+3=14 X_A = \dfrac{1}{1+3} = \dfrac{1}{4} XB=31+3=34 X_B = \dfrac{3}{1+3} = \dfrac{3}{4} Plug these into the equation: 500=200×14+PBo×34 500 = 200 \times \dfrac{1}{4} + P_B^o \times \dfrac{3}{4} Simplifying: 500=50+34PBo 500 = 50 + \dfrac{3}{4} P_B^o Subtract 50 from both sides: 450=34PBo 450 = \dfrac{3}{4} P_B^o Multiply both sides by 43\dfrac{4}{3} to solve for PBoP_B^o: PBo=600mm Hg P_B^o = 600 \, \text{mm Hg} Since PAoInconclusion:ThevaporpressureofpureB, P_A^o In conclusion: The vapor pressure of pure B, P_B^o $, is 600 mm Hg.

The least volatile component is A.

Q84
For which of the following parameters the structural isomers C2H5OH and CH3OCH3 would be expected to have the same values? (Assume ideal behaviour)
A Heat of vaporization
B Gaseous densities at the same temperature and pressure
C Boiling points
D Vapour pressure at the same temperature
Correct Answer
Option B
Solution

Gaseous densities of ethanol and dimethyl ether would be same at same temperature and pressure.

The heat of vaporisation ,

V.P.V.P.

and

b.ptsb.pts

will differ due to

HH

-bonding in ethanol.

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