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 2
Q51jee_main_2026_22_january_eveningMole Fraction and Concentration Terms
At T(K)$T(\text{K})$, 100 g$100\text{ g}$ of 98% H₂SO₄ (w/w)$98\% \text{ H}_2\text{SO}_4\text{ (w/w)}$ aqueous solution is mixed with 100 g$100\text{ g}$ of 49% H₂SO₄ (w/w)$49\% \text{ H}_2\text{SO}_4\text{ (w/w)}$ aqueous solution. What is the mole fraction of H₂SO₄$\text{H}_2\text{SO}_4$ in the resultant solution?
(Given: Atomic mass H = 1 u$\text{H} = 1\text{ u}$; S = 32 u$\text{S} = 32\text{ u}$; O = 16 u$\text{O} = 16\text{ u}$)
(Assume that temperature after mixing remains constant)
A.0.9$0.9$
B.0.1$0.1$
C.0.337$0.337$
D.0.663$0.663$
Solution
Related Formula
Mass of solute = Total mass of solution × Percentage (w/w)100$$\text{Mass of solute} = \text{Total mass of solution} \times \frac{\text{Percentage (w/w)}}{100}$$Mole fraction (xA) = (nA)/(nA + nB)$$\text{Mole fraction } (x_A) = \frac{n_A}{n_A + n_B}$$
where,
nA$n_A$ = moles of solute (H₂SO₄$\text{H}_2\text{SO}_4$)
nB$n_B$ = moles of solvent (H₂O$\text{H}_2\text{O}$)
Core Logic
Step 1: Calculate total weight of H₂SO₄$\text{H}_2\text{SO}_4$:
Sees: Mixing two solution concentrations (w/w).
Shortcut: Sum the component masses directly to find total solute mass and total solvent mass, then apply standard mole fraction formula.
Chapter Mix
Class 12 Chemistry: Solutions
Class 11 Chemistry: Some Basic Concepts of Chemistry
Q52jee_main_2026_23_january_morningNon-Ideal Solutions and Raoult's Law
Which one of the following graphs accurately represents the plot of partial pressure of CS₂$CS_{2}$ vs its mole fraction in a mixture of acetone and CS₂$CS_{2}$ at constant temperature?
A mixture of carbon disulfide (CS₂$CS_2$) and acetone (CH₃-CO-CH₃$CH_3-CO-CH_3$) shows a positive deviation from Raoult's Law. This happens because the dipole-dipole interactions between acetone and CS₂$CS_2$ are weaker than the attractive interactions between the pure molecules themselves.
Step 1: Graph Interpretation
Due to positive deviation, the actual partial pressure curve will bulge upwards (convex) relative to the ideal straight line (Raoult's Law). The first graph precisely depicts this upward curve starting from zero and reaching P^°CS₂$P^\circ_{CS_2}$.
Pattern Recognition
Acetone + Carbon disulfide = Positive Deviation. Positive deviation means vapor pressure is higher than expected, so the curve sags upwards above the straight-line prediction.
Chapter Mix
Class 12 Chemistry: Solutions
Q72jee_main_2026_23_january_eveningRaoult's Law
Two liquids A and B form an ideal solution. At 320 K$320 \text{ K}$, the vapour pressure of the solution, containing 3 mol of A and 1 mol of B is 500 mm Hg$500 \text{ mm Hg}$. At the same temperature, if 1 mol of A is further added to this solution, vapour pressure of the solution increases by 20 mm Hg$20 \text{ mm Hg}$. Vapour pressure (in mm Hg$\text{mm Hg}$) of B in the pure state is ____. (Nearest integer)
Case 1:
Moles of A (nA$n_A$) = 3, Moles of B (nB$n_B$) = 1.
Total moles = 3 + 1 = 4$3 + 1 = 4$.
Mole fraction of A (XA$X_A$) = (3)/(4)$\frac{3}{4}$, Mole fraction of B (XB$X_B$) = (1)/(4)$\frac{1}{4}$.
Vapour pressure (Pₛ$P_{\text{s}}$) = 500 mm Hg$500 \text{ mm Hg}$.
Using Raoult's law:
Case 2:
1 mol of A is further added. So, new moles of A (nA$n_A^{\prime}$) = 4. Moles of B remains 1.
Total moles = 4 + 1 = 5$4 + 1 = 5$.
Mole fraction of A (XA$X_A^{\prime}$) = (4)/(5)$\frac{4}{5}$, Mole fraction of B (XB$X_B^{\prime}$) = (1)/(5)$\frac{1}{5}$.
Vapour pressure increases by 20 mm Hg$20 \text{ mm Hg}$, so new Pₛ = 500 + 20 = 520 mm Hg$P_{\text{s}} = 500 + 20 = 520 \text{ mm Hg}$.
Using Raoult's law:
A standard two-equation Raoult's law system. Cross-multiply out the denominators immediately to get simple linear equations (Ax + By = C$Ax + By = C$) which allow straightforward elimination.
A solution is prepared by dissolving 0.3 g$0.3 \text{ g}$ of a non-volatile non-electrolyte solute 'A' of molar mass 60 g mol⁻¹$60 \text{ g mol}^{-1}$ and 0.9 g$0.9 \text{ g}$ of a non-volatile non-electrolyte solute 'B' of molar mass 180 g mol⁻¹$180 \text{ g mol}^{-1}$ in 100 mL$100 \text{ mL}$H₂O$\mathrm{H}_2\mathrm{O}$ at 27°C$27^{\circ}\text{C}$. Osmotic pressure of the solution will be
[Given: R = 0.082 L atm K⁻¹ mol⁻¹$R = 0.082 \text{ L atm K}^{-1} \text{ mol}^{-1}$]
For non-electrolytes, i=1$i=1$. Add the moles of all solutes present to find the total effective molarity. Use T = 300 K$T = 300 \text{ K}$ for 27°C$27^{\circ}\text{C}$.
'W' g of a non-volatile electrolyte solid solute of molar mass 'M' g mol⁻¹$g \text{ mol}^{-1}$ when dissolved in 100 mL$100 \text{ mL}$ water, decreases vapour pressure of water from 640 mm Hg$640 \text{ mm Hg}$ to 600 mm Hg$600 \text{ mm Hg}$. If aqueous solution of the electrolyte boils at 375 K$375 \text{ K}$ and Kb$K_b$ for water is 0.52 K kg mol⁻¹$0.52 \text{ K kg mol}^{-1}$, then the mole fraction of the electrolyte solute(X₂)$(X_2)$ in the solution can be expressed as
(Given : density of water = 1 g/mL$1 \text{ g/mL}$ and boiling point of water = 373 K$373 \text{ K}$)
Δ PP° = i · Xsolute$$\frac{\Delta P}{P^{\circ}} = i \cdot X_{\text{solute}}$$Δ Tb = i · Kb · m$$\Delta T_b = i \cdot K_b \cdot m$$
Core Logic
From Relative Lowering of Vapour Pressure:
P° = 640 mm Hg$P^{\circ} = 640 \text{ mm Hg}$Pₛ = 600 mm Hg$P_s = 600 \text{ mm Hg}$Δ P = 40 mm Hg$\Delta P = 40 \text{ mm Hg}$
Moles of solute n = (W)/(M)$n = \frac{W}{M}$
Mole fraction Xsolute = Δ PP° · (1)/(i)$X_{\text{solute}} = \frac{\Delta P}{P^{\circ}} \cdot \frac{1}{i}$ (for dilute solutions, or properly i · Xsolute = Δ PP°$i \cdot X_{\text{solute}} = \frac{\Delta P}{P^{\circ}}$ as given in the pdf approach)
Δ PP° = i · Xsolute Xsolute = (40)/(640) × (1)/(i)$\frac{\Delta P}{P^{\circ}} = i \cdot X_{\text{solute}} \implies X_{\text{solute}} = \frac{40}{640} \times \frac{1}{i}$
Now, from Boiling Point Elevation:
Δ Tb = 375 - 373 = 2 K$\Delta T_b = 375 - 373 = 2 \text{ K}$m = moles of solutemass of solvent in kg = (W/M)/(100/1000) = (W)/(M) × 10$m = \frac{\text{moles of solute}}{\text{mass of solvent in kg}} = \frac{W/M}{100/1000} = \frac{W}{M} \times 10$Δ Tb = i × Kb × m$\Delta T_b = i \times K_b \times m$2 = i × 0.52 × ( (W/M)/(100) × 1000 )$2 = i \times 0.52 \times \left( \frac{W/M}{100} \times 1000 \right)$i = (2)/(5.2) × (M)/(W)$i = \frac{2}{5.2} \times \frac{M}{W}$
Step 1: Calculate Mole Fraction
Substitute the value of i$i$ into the Xsolute$X_{\text{solute}}$ equation:
When an unknown electrolyte is involved, isolate the van't Hoff factor (i$i$) from one colligative property equation and substitute it into the other to eliminate i$i$ and solve for the target variable.
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.