Negative Deviation from Raoult's Law Maximum Boiling Azeotrope$$\text{Negative Deviation from Raoult's Law} \implies \text{Maximum Boiling Azeotrope} $$Positive Deviation from Raoult's Law Minimum Boiling Azeotrope$$\text{Positive Deviation from Raoult's Law} \implies \text{Minimum Boiling Azeotrope} $$Ideal Solution Δ Vmix = 0$$\text{Ideal Solution} \implies \Delta V{\text{mix}} = 0 $$
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$\rightarrow$ (III)
- (B) Ethanol and Water: Exhibit hydrogen bond disruptions, leading to positive deviation, forming a minimum boiling azeotrope arrow$\rightarrow$ (I)
- (C) Benzene and Toluene: Highly structurally similar, forming a near-perfect ideal solution where Δ Vmix = 0$\Delta V{\text{mix}} = 0$arrow$\rightarrow$ (IV)
- (D) Acetic acid in benzene: Acetic acid undergoes intermolecular hydrogen bonding inside the non-polar solvent, causing it to dimerize arrow$\rightarrow$ (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$i=0.5$). Benzene-toluene is the most famous ideal solution pair. Recognizing either instantly shortcuts the options list to the correct key.
Keywords:#maximum boiling azeotrope example#JEE Main 2025 Evening Q38#acetic acid dimerization benzene#ideal solutions delta V mix
More Solutions Previous-Year Questions — Page 3
Q54jee_main_2026_24_january_eveningVapour Pressure of Liquid Solutions
Two liquids A and B form an ideal solution at temperature T K. At T K, the vapour pressures of pure A and B are 55 and 15kNm⁻²$15\mathrm{kNm}^{-2}$ respectively. What is the mole fraction of A in solution of A and B in equilibrium with a vapour in which the mole fraction of A is 0.8?
When dealing with equilibrium between liquid and vapour states, taking the ratio (YA)/(YB) = (PA)/(PB)$\frac{Y_A}{Y_B} = \frac{P_A}{P_B}$ bypasses finding the total pressure Ptotal$P_{\text{total}}$ directly and simplifies fraction algebra.
Chapter Mix
Class 12 Chemistry: Solutions
Q68jee_main_2026_24_january_eveningHenry's Law
At 298 K, the mole percentage of N₂(g)$N_{2}(g)$ in air is 80%. Water is in equilibrium with air at a pressure of 10 atm. What is the mole fraction of N₂(g)$N_{2}(g)$ in water at 298 K? ( KH$K_{H}$ for N₂$N_{2}$ is 6.5 × 10⁷$6.5 \times 10^{7}$ mm Hg)
Always align the pressure units. Since KH$K_H$ dictates the unit ecosystem, convert Pgas$P_{\text{gas}}$ to match KH$K_H$ (e.g., atm to mm Hg via × 760$\times 760$).
Chapter Mix
Class 12 Chemistry: Solutions
Q53jee_main_2026_28_january_morningRaoults Law for Binary Mixtures
At T(K), 2$2$ moles of liquid A and 3$3$ moles of liquid B are mixed. The vapour pressure of ideal solution formed is 320~mm~Hg$320\mathrm{~mm~Hg}$. At this stage, one mole of A and one mole of B are added to the solution. The vapour pressure is now measured as 328.6~mm~Hg$328.6\mathrm{~mm~Hg}$. The vapour pressure (in mm~Hg$\mathrm{mm~Hg}$) of A and B are respectively:
Consider the following aqueous solutions.
I. 2.2 g$2.2\text{ g}$ Glucose in 125 mL$125\text{ mL}$ of solution.
II. 1.9 g$1.9\text{ g}$ Calcium chloride in 250 mL$250\text{ mL}$ of solution.
III. 9.0 g$9.0\text{ g}$ Urea in 500 mL$500\text{ mL}$ of solution.
IV. 20.5 g$20.5\text{ g}$ Aluminium sulphate in 750 mL$750\text{ mL}$ of solution.
The correct increasing order of boiling point of these solutions will be:
[Given: Molar mass in g mol⁻¹$\text{g mol}^{-1}$: H=1, C=12, N=14, O=16, Cl=35.5, Ca=40, Al=27 and S=32$H=1, C=12, N=14, O=16, Cl=35.5, Ca=40, Al=27\text{ and }S=32$]
A.(1) I < II < III < IV$(1)\text{ I < II < III < IV}$
B.(2) III < I < II < IV$(2)\text{ III < I < II < IV}$
C.(3) II < III < I < IV$(3)\text{ II < III < I < IV}$
D.(4) II < III < IV < I$(4)\text{ II < III < IV < I}$
Solution
Related Formula
Δ Tb = i · Kb · m$$\Delta T_b = i \cdot K_b \cdot m$$
For dilute solutions, Molarity (M) ≈$\approx$ Molality (m).
Thus, Δ Tb ∝ i × M$\Delta T_b \propto i \times M$
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$i$). Do not compare just raw mass or raw molarity.
Chapter Mix
Class 12 Chemistry: Solutions
Q37jee_main_2025_02_april_eveningMolarity and Temperature Dependency
'x' g of NaCl is added to water in a beaker with a lid. The temperature of the system is raised from 1°C$1^{\circ}\mathrm{C}$ to 25°C$25^{\circ}\mathrm{C}$. Which out of the following plots, is best suited for the change in the molarity (M) of the solution with respect to temperature?
[Consider the solubility of NaCl remains unchanged over the temperature range]
Since solubility of NaCl$\mathrm{NaCl}$ remains unchanged, the number of dissolved moles of NaCl$\mathrm{NaCl}$ solute (nsolute$n_{\text{solute}}$) remains strictly constant. Thus, molarity M$M$ is strictly dependent on the volume of water (solvent) as temperature changes:
M ∝ 1Vsolution$$M \propto \frac{1}{V_{\text{solution}}}$$
Step 1: Understand Water's Anomalous Expansion
Water exhibits unique anomalous density behavior near freezing:
From 1°C$1^{\circ}\mathrm{C}$ to 4°C$4^{\circ}\mathrm{C}$, the density of water increases to a maximum. This contraction means the volume (V$V$) of water decreases.
From 4°C$4^{\circ}\mathrm{C}$ to 25°C$25^{\circ}\mathrm{C}$, the density of water decreases due to standard thermal expansion. Consequently, the volume (V$V$) increases.
Step 2: Relate Volume to Molarity
Because volume is in the denominator of the molarity equation:
From 1°C$1^{\circ}\mathrm{C}$ to 4°C$4^{\circ}\mathrm{C}$: Volume decreases $\implies$ Molarity increases.
At 4°C$4^{\circ}\mathrm{C}$: Volume is minimum $\implies$ Molarity reaches a maximum.
From 4°C$4^{\circ}\mathrm{C}$ to 25°C$25^{\circ}\mathrm{C}$: Volume increases $\implies$ Molarity decreases.
This behavior is perfectly represented by Plot (2), which features a distinct peak around 4°C$4^{\circ}\mathrm{C}$.
Pattern Recognition
Water is at its densest (and occupies minimum volume) at exactly 3.98^$3.98^\circ\mathrm{C}$ (4^$4^\circ\mathrm{C}$). Any concentration unit based on volume (such as Molarity or Normality) will reach a corresponding maximum at this temperature.
Chapter Mix
Class 12 Chemistry: Solutions
More Solutions Questions — jee_main_2025_07_april_evening
Practice past-year questions one chapter at a time. Pick an exam → subject → chapter and get every PYQ for that topic — pulled together from all past papers — with the chapter's key formulas alongside.