Chem notesPhysicalSolid, Solutions & Surface
Independent topic page
Use unit-cell ownership, solvent chemical-potential lowering and surface coverage as three separate models; mixed statement sets then become fast audits.
01. Crystal questions require fractional ownership: corner 1/8, face 1/2, edge 1/4, body centre 1. The seven crystal systems (a,b,c,α,β,γ) fix the lattice type; packing questions usually focus on cubic and hexagonal close packing.
02. Point defects must preserve the stated charge and stoichiometry. Schottky lowers density; Frenkel relocates ions and approximately preserves density. Radius-ratio rules guide coordination in ionic solids when the stem invites that check.
03. Raoult's law defines ideal-solution behaviour. Colligative properties depend on solute particle count, so van't Hoff factor diagnoses association or dissociation — a frequent Advanced numerical.
04. Adsorption is a surface phenomenon: physisorption is weak, multilayer-capable and reversible; chemisorption is specific, activated and often monolayer. Freundlich is an empirical moderate-pressure isotherm. Colloids, emulsions, surfactants and micelles appear as definition-plus-property stems.
05. Solid-state packing is geometry plus stoichiometry: voids, density and formula units per cell must agree with the lattice type before any numerical.
06. Colligative properties track particle moles after van ’t Hoff i — not formula moles of undissociated solute.
07. Adsorption and colloids reward classification first: physisorption vs chemisorption, lyophilic vs lyophobic, then isotherm or charge logic.
Official · 2026
Official syllabus points for Solid State, Solutions & Surface Chemistry only — not the full Physical portion map. Portion hub: Physical · Physical analysis.
Source: https://jeeadv.ac.in/documents/jee-advanced-2026-syllabus.pdf
Exam focusfcc/bcc/hcp packing, colligative + van’t Hoff, adsorption isotherm basics.
Syllabus points
Do / check
2020–2026 paper weight
Topic match inside parent portion Physical (49.8% of Chemistry tags). Stats below are portion backdrop; matched subtopics show where Solid State, Solutions & Surface Chemistry sits.
Portion-wide type/difficulty mix lives on the Physical analysis — not repeated here so this page stays on Solid, Solutions & Surface.
Cross-topic stems
Advanced rarely asks a chapter in isolation. These are tagged multi-idea Chemistry stems that touch Solid State, Solutions & Surface Chemistry — practise the knowledge bridge, not only the single-chapter drill.
Step 1: from the linked ideal-solution data, compute the vapour-to-liquid molar volume ratio for pure B. Step 2: find liquid mole fractions (e.g. from molality). Step 3: apply Raoult to get y_B in the vapour (numerical ~0.16 style).
Two numericals share solution data; unit slips (molality vs mole fraction) are common.
Convert every molality stem to x_i before touching vapour pressures.
Why methods matter
Unit discipline and particle bookkeeping connect crystal, solution and surface questions.
Prevents memorised Z from failing on decorated or ionic cells.
Do thisCount each lattice site by its shared fraction before using Z.
Prevents memorised Z from failing on decorated or ionic cells.
Eight corners contribute 8×1/8=1; six face centres contribute 6×1/2=3, total fcc Z=4.
Derives a–r relations instead of swapping fcc and bcc formulas.
Do thisDraw the face/body diagonal where spheres touch and apply Pythagoras.
Derives a–r relations instead of swapping fcc and bcc formulas.
fcc touches along face diagonal: √2a=4r; bcc along body diagonal: √3a=4r.
Separates thermodynamic measurement from association/dissociation stoichiometry.
Do thisConvert solute chemistry to effective particle moles through i before colligative formulas.
Separates thermodynamic measurement from association/dissociation stoichiometry.
Complete CaCl₂ dissociation ideally gives i≈3; benzoic-acid dimerisation gives i<1.
Predicts sign of Raoult deviation and azeotrope tendency causally.
Do thisCompare A–B attractions with A–A and B–B before ranking vapour pressure.
Predicts sign of Raoult deviation and azeotrope tendency causally.
Weaker A–B interactions increase escaping tendency: positive deviation, higher P and possible minimum-boiling azeotrope.
Processed examples
Read the impact line first. Then notice which family/model was chosen. The solution is written the way your rough sheet should look in the hall.
An fcc metal has edge 400 pm and molar mass 64 g mol⁻¹. Find density.
This stem rewards early recognition of the crystal density and unit cell model.
Model chosenUse Z=4 in the unit-cell equation.
Answer6.64 g cm⁻³
Takeaway: Convert edge length before cubing.
A solute dimerizes 60% in benzene. Find its van’t Hoff factor.
This stem rewards early recognition of the colligative molar mass model.
Model chosenCount particles after association.
Answer0.70
Takeaway: Association lowers particle count and i.
An MO crystal is doped with 10 mol% M₂O₃ relative to total metal ions. Assuming cation vacancies provide charge balance, find vacancies per 100 occupied metal sites.
This Advanced-level variation couples hidden constraints with the defects and stoichiometry model.
Model chosenBalance the excess positive charge of M³⁺ with missing M²⁺ ions.
Answer5 cation vacancies
Takeaway: Aliovalent defects are fixed by charge neutrality.
Reusable models
Advanced stems cluster. Name the family in 10–15s, write the fast model, then run the same path. Do not invent a new plan each time.
Looks likeEdge length, density, Z or molar mass
Fast modelUse ρ=ZM/(a³Nₐ) with one unit system.
Recognition fixes the model before arithmetic begins.
Do not start blind expansion or casework before identifying the governing model.
Looks likeVacancies, interstitials or aliovalent doping
Fast modelEnforce charge neutrality per formula unit.
Recognition fixes the model before arithmetic begins.
Do not start blind expansion or casework before identifying the governing model.
Looks likeAssociation/dissociation, freezing or osmotic data
Fast modelExtract van’t Hoff factor before molar mass.
Recognition fixes the model before arithmetic begins.
Do not start blind expansion or casework before identifying the governing model.
Looks likeFreundlich isotherm, coagulation or micelles
Fast modelIdentify the governing empirical law or charge rule.
Recognition fixes the model before arithmetic begins.
Do not start blind expansion or casework before identifying the governing model.
Hall timing
Underline data, units, phase/standard-state labels and the exact quantity asked. Reject any formula whose assumptions are already violated.
Write the governing relation symbolically before substitution; define one basis, reference state, or extent variable if the stem mixes quantities.
Keep ratios and logarithms exact as long as possible. Carry signs, powers of ten and units on the rough sheet instead of repairing them later.
Check dimensions, limiting cases and chemical sense. For multi-correct, test every option independently rather than forcing one common conclusion.
After the model is locked
ρ=Z M/(N_A a³)
Cubic cell with edge a and Z formula units per cell
sc: a=2r, Z=1; bcc: √3a=4r, Z=2; fcc: √2a=4r, Z=4
Monatomic cubic packing
sc: 52.4%, CN6; bcc: 68.0%, CN8; fcc/hcp: 74.0%, CN12
Standard close-packing comparison
p_i=x_i p_i°; P=Σx_i p_i°
Ideal volatile-liquid solution
p=K_H x (common convention)
Dilute gas dissolved in liquid; use stated convention
ΔT_b=iK_bm; ΔT_f=iK_fm; π=iCRT; relative lowering=(p°−p)/p°=x_solute
Dilute solution particle-count effects
i=observed colligative property/calculated; dissociation to ν particles: i=1+(ν−1)α; dimerisation: i=1−α/2
Association/dissociation
x/m=kP^(1/n); log(x/m)=log k+(1/n)log P, 0<1/n<1
Empirical adsorption over moderate pressure range
Make it automatic