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Solutions appeared 45 times across 3 years — 5.2% of Chemistry. This question is from Colligative Properties.

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Questions 14 20 11 45

Consider the following aqueous solutions. I. 2.2 g Glucose in 125 mL of solution. II. 1.9 g Calcium chloride in 250 mL of solution. III. 9.0 g Urea in 500 mL of solution. IV. 20.5 g Aluminium sulphate in 750 mL of solution. The correct increasing order of boiling point of these solutions will be: [Given: Molar mass in g mol⁻¹: H=1, C=12, N=14, O=16, Cl=35.5, Ca=40, Al=27 and S=32]

Solution & Explanation

Related Formula
Δ Tb = i · Kb · m

For dilute solutions, Molarity (M) ≈ Molality (m). Thus, Δ Tb ∝ i × M

Core Logic

SolutionMolarity (M = (W)/(Mw) × (1000)/(V))Effective Concentration (i × M)
(I) Glucose (i=1)(2.2)/(180) × (1000)/(125) = 0.098 M1 × 0.098 = 0.098
(II) CaCl₂ (i=3)(1.9)/(111) × (1000)/(250) = 0.068 M3 × 0.068 = 0.204
(III) Urea (i=1)(9)/(60) × (1000)/(500) = 0.3 M1 × 0.3 = 0.300
(IV) Al₂(SO₄)₃ (i=5)(20.5)/(342) × (1000)/(750) = 0.080 M5 × 0.080 = 0.400

Step 1: Compare Effective Concentrations

Comparing the values of i × M: 0.098 < 0.204 < 0.300 < 0.400 ⇒ Glucose (I) < CaCl₂ (II) < Urea (III) < Al₂(SO₄)₃ (IV)

Step 2: Final Conclusion

Order of boiling points corresponds directly to effective concentration. Thus: I < II < III < IV.

Pattern Recognition

For multiple salt mixtures, always multiply molarity by the Van't Hoff factor (i). Do not compare just raw mass or raw molarity.

Chapter Mix

Class 12 Chemistry: Solutions

Reference Study Guides

More Solutions Previous-Year Questions — Page 6

Q46 jee_main_2025_04_april_evening Concentration Terms
Sea water, which can be considered as a 6 molar (6 M) solution of NaCl, has a density of 2~g~mL⁻¹ . The concentration of dissolved oxygen (O₂) in sea water is 5.8~ppm . Then the concentration of dissolved oxygen (O₂) in sea water, is x × 10⁻⁴m . x = _______. (Nearest integer) Given: Molar mass of NaCl is 58.5~g~mol⁻¹ Molar mass of O₂ is 32~g~mol⁻¹
Numerical Answer. Answer: 1.9 to 2.1

Solution

Related Formula
ppm = mass of solutemass of solution × 10⁶ Molality (m) = moles of solutemass of solvent in kg
Core Logic
  • Consider 1000 ~mL of seawater solution:
Mass of solution = Volume × density = 1000 × 2 = 2000 ~g Mass of NaCl = 6 moles × 58.5 = 351 ~g Mass of solvent (water) = 2000 - 351 = 1649 ~g = 1.649 ~kg
  • Compute the mass and moles of dissolved O₂ using the ppm value:
ppm = 5.8 = mass of O₂2000 × 10⁶ mass of O₂ = 1.16 × 10⁻² ~g moles of O₂ = 1.16 × 10⁻²32 = 3.625 × 10⁻⁴ moles
  • Determine the molality (m) of oxygen:
molality = 3.625 × 10⁻⁴1.649 ≈ 2.19 × 10⁻⁴ ~m

Matching the pattern x × 10⁻⁴m, we get x ≈ 2.19. The nearest integer is 2.

Pattern Recognition

For high concentration saline solutions, the mass of the solvent drops significantly below the total mass of the solution. Be careful to subtract the solute weight (351 ~g) before computing molality.

Chapter Mix

Class 12 Chemistry: Solutions

Q26 jee_main_2025_04_april_morning Reverse Osmosis
XY is the membrane / partition between two chambers 1 and 2 containing sugar solutions of concentration c₁ and c₂ (c₁ > c₂) mol~L⁻¹. For the reverse osmosis to take place identify the correct condition (Here p₁ and p₂ are pressures applied on chamber 1 and 2):
Reverse Osmosis cell partition diagram for Q26 - JEE Main 2025 Morning
The diagram illustrates two chambers separated by a membrane XY containing sugar solutions of concentrations c1 and c2.
  • A. (B) and (D) only
  • B. (A) and (D) only
  • C. (A) and (C) only
  • D. (C) only

Solution

Related Formula

π = c R T

where π is the osmotic pressure of the solution.

Core Logic

Given that c₁ > c₂, chamber 1 has a higher concentration of solute than chamber 2. Under normal conditions, solvent molecules spontaneously flow from lower concentration (chamber 2) to higher concentration (chamber 1) via osmosis.

To achieve reverse osmosis, the solvent must flow in the opposite direction—from chamber 1 to chamber 2. This requires applying an external pressure on the higher concentration side (chamber 1) that exceeds its osmotic pressure π.

Condition for Reverse Osmosis: p₁ > π

Cellophane and parchment paper both act as suitable semi-permeable membranes for this setup. Thus, statements (A) and (C) are correct.

Pattern Recognition

Reverse osmosis always requires external pressure applied on the concentrated solution side (chigh) such that Papplied > π.

Chapter Mix

Class 12 Chemistry: Solutions

Q34 jee_main_2025_07_april_evening Raoult's Law and Liquid-Vapour Composition
Liquid A and B form an ideal solution. The vapour pressure of pure liquids A and B are 350 and 750 mm Hg respectively at the same temperature. If xA and xB are the mole fraction of A and B in solution while yA and yB are the mole fraction of A and B in vapour phase then:
  • A. xAxB < yAyB
  • B. xAxB = yAyB
  • C. xAxB > yAyB
  • D. (xA - yA) < (xB - yB)

Solution

Related Formula
PA = yA Ptotal = xA P⁰A PB = yB Ptotal = xB P⁰B

Dividing both partial pressure formulations yields:

yAyB = ( P⁰AP⁰B) · xAxB
Core Logic

Given pure saturation thresholds:

P⁰A = 350 mm Hg, P⁰B = 750 mm Hg

Comparing pure component volatility profiles:

P⁰A < P⁰B P⁰AP⁰B < 1

Substituting this inequality into the ratio formula gives:

yAyB < 1 · xAxB yAyB < xAxB
Step 1: Rearranging Ratio Forms

Inverting the inequality expression fields safely yields:

xAxB > yAyB
Pattern Recognition

Konovalov's Rule Shortcut: The vapour phase is always enriched with the more volatile component. Since component B has a higher pure vapour pressure (750 > 350), it will be preferentially enriched in the vapour phase, meaning yB/yA > xB/xA. Reversing the fractions directly matches option (3).

Chapter Mix

Class 12 Chemistry: Solutions

Q38 jee_main_2025_07_april_evening Azeotropes and Liquid Mixtures
Match List-I with List-II
List-I List-II (A) Solution of chloroform and acetone (I) Minimum boiling azeotrope (B) Solution of ethanol and water (II) Dimerizes (C) Solution of benzene and toluene (III) Maximum boiling azeotrope (D) Solution of acetic acid in benzene (IV) Δ Vmix=0 Choose the correct answer from the options given below:
  • A. (A)-(III), (B)-(I), (C)-(IV), (D)-(II)
  • B. (A)-(II), (B)-(IV), (C)-(I), (D)-(III)
  • C. (A)-(III), (B)-(IV), (C)-(I), (D)-(II)
  • D. (A)-(II), (B)-(I), (C)-(IV), (D)-(III)

Solution

Related Formula
Negative Deviation from Raoult's Law Maximum Boiling Azeotrope Positive Deviation from Raoult's Law Minimum Boiling Azeotrope Ideal Solution Δ Vmix = 0
Core Logic

Evaluating molecular interaction behaviors: - (A) Chloroform and Acetone: Form intermolecular hydrogen bonds, showing negative deviation from Raoult's law, which forms a maximum boiling azeotrope arrow (III) - (B) Ethanol and Water: Exhibit hydrogen bond disruptions, leading to positive deviation, forming a minimum boiling azeotrope arrow (I) - (C) Benzene and Toluene: Highly structurally similar, forming a near-perfect ideal solution where Δ Vmix = 0 arrow (IV) - (D) Acetic acid in benzene: Acetic acid undergoes intermolecular hydrogen bonding inside the non-polar solvent, causing it to dimerize arrow (II)

Step 1: Alignment Selection

Combining the pairs gives: (A)-(III), (B)-(I), (C)-(IV), (D)-(II).

Pattern Recognition

Liquid properties shortcut: Acetic acid in benzene is a classic textbook example of dimerization (i=0.5). Benzene-toluene is the most famous ideal solution pair. Recognizing either instantly shortcuts the options list to the correct key.

Chapter Mix

Class 12 Chemistry: Solutions

Q46 jee_main_2025_24_jan_evening Abnormal Molar Masses and Van't Hoff Factor
The observed and normal masses of compound MX₂ are 65.6 and 164 respectively. The percent degree of ionisation of MX₂ is ____ %. (Nearest integer)
Numerical Answer. Answer: 75 to 75

Solution

Related Formula
i = Normal Molar MassObserved Molar Mass i = 1 + (n - 1)α
Core Logic
  • Calculate the van 't Hoff factor (i):
i = (164)/(65.6) = 2.5
  • Set up the dissociation equilibrium for the electrolyte MX₂:
MX₂ arrow M²⁺ + 2X⁻

Here, 1 molecule dissociates into n = 1 + 2 = 3 ions.

  • Relate i to the degree of ionization (α):
i = 1 + (3 - 1)α = 1 + 2α 2.5 = 1 + 2α 2α = 1.5 α = 0.75
  • Convert to a percentage:
Percent dissociation = 0.75 · 100 = 75%
Pattern Recognition

For a salt that dissociates into three ions (like MX₂), the relationship simplifies to i = 1 + 2α. Calculating i from the ratio of the molar masses lets you find α directly.

Chapter Mix

Class 12 Chemistry: Solutions

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