NDA Chemistry · Free notes
Matter and Its States — NDA Chemistry
Matter and Its States is the foundation chapter of NDA Chemistry — 32 PYQs across 2017–2026, almost all EASY or MODERATE, and almost all pure named-fact recall and classification. The bank loves three shapes here: 'which is NOT a mixture / solution / chemical change', 'which phase change is this' (dry ice, sulphur crust), and 'match the separation method to the mixture'. The win comes from knowing the classification trees and the phase-change names cold, not from any calculation. The chapter teaches in five movements, building from what matter is up to how we pull mixtures apart: (1) States of matter, phase changes and diffusion — solid, liquid, gas, the six interconversion names (melting, freezing, vaporisation, condensation, sublimation, deposition), and why dry ice is the bank's favourite example; (2) Physical vs chemical changes — the one test (is a new substance formed?) and the everyday examples on each side; (3) Compounds, mixtures and solutions — the pure-substance vs mixture tree, homogeneous vs heterogeneous, and mass-percentage of a solution; (4) Colloids and suspensions — the particle-size ladder (solution → colloid → suspension), the Tyndall effect, and soap micelles; (5) Separation techniques — distillation, fractional distillation, separating funnel, centrifugation, chromatography, sublimation, evaporation and crystallization, each matched to the mixture it separates. 13 concepts, every PYQ tagged. Most concepts are reference tables: memorise the table, win the marks.
The handout has every subtopic, worked example, formula and trap with answers shown. The formula sheet is the chapter’s formulas and traps alone, on one page.
Subtopic notes
States of Matter, Phase Changes and Diffusion
7 PYQsMatter exists as solid, liquid or gas depending on how tightly its particles are held; adding or removing heat moves it between these states through six named phase changes, and particles spread on their own by diffusion.
Physical vs Chemical Changes
4 PYQsA physical change alters only the form or state of a substance and is usually reversible; a chemical change makes a brand-new substance with new properties and is usually irreversible.
Compounds, Mixtures and Solutions
7 PYQsMatter is either a pure substance (element or compound, fixed composition) or a mixture (two or more substances physically mixed); mixtures are homogeneous (uniform, like a solution) or heterogeneous (non-uniform).
Colloids and Suspensions
7 PYQsBetween true solutions (tiny dissolved particles) and suspensions (large settling particles) sit colloids — particles big enough to scatter light (the Tyndall effect) but small enough not to settle; soap in water is a colloid of micelles.
Separation Techniques
7 PYQsMixtures are pulled apart by physical methods chosen to exploit a difference between the components — boiling point (distillation), density/immiscibility (separating funnel, centrifugation), or volatility and solubility (sublimation, evaporation, crystallization).
Formula & revision sheet
1 formulas · 12 reference tables · 19 gotchas across all subtopics — the exam-eve cheat-sheet
Formula & revision sheet
1 formulas · 12 reference tables · 19 gotchas across all subtopics — the exam-eve cheat-sheet
Reference tables (4)
The three states of matter4 rows
| State | Shape | Volume | Compressibility |
|---|---|---|---|
| Solid | Fixed | Fixed | Almost none |
| Liquid | Takes container's shape | Fixed | Almost none |
| Gas | Takes container's shape | Fills container | High |
| Liquid elements at 25 °C | — | — | — Only mercury (Hg) and bromine (Br₂) are liquid at room temperature and normal pressure. Gallium and caesium are solids at 25 °C (they melt only just above it). |
The six phase changes6 rows
| Phase change | Direction | Heat | Example |
|---|---|---|---|
| Melting | Solid → liquid | Absorbed | Ice → water |
| Freezing | Liquid → solid | Released | Water → ice |
| Vaporisation | Liquid → gas | Absorbed | Water → steam |
| Condensation | Gas → liquid | Released | Steam → water droplets |
| Sublimation | Solid → gas | Absorbed | Dry ice → CO₂ gas; camphor Sublimation skips the liquid state entirely — solid goes straight to gas. |
| Deposition | Gas → solid | Released | Sulphur vapour → solid crust; frost Deposition is the reverse of sublimation: gas straight to solid, no liquid. |
Dry ice — solid carbon dioxide4 rows
| Question asked | Answer |
|---|---|
| What is dry ice? | Solid carbon dioxide (CO₂) |
| Is dry ice frozen water? | No — it is solid CO₂ |
| Phase change when dry ice 'disappears' | Sublimation (solid → gas) Dry ice never melts to a liquid at normal pressure — it sublimes straight to gas. |
| Why mist forms on a stage | Cold CO₂ gas condenses atmospheric water vapour |
Diffusion3 rows
| State | Diffusion rate | Everyday example |
|---|---|---|
| Gas | Fastest | Perfume smell spreading across a room |
| Liquid | Moderate | Ink drop colouring water |
| Solid | Slowest (negligible) | Two metals welded together over years Solids diffuse extremely slowly because their particles are locked in place. |
Watch out for (4)
- Gallium is a solid at room temperature→ The three states of matter
- Boiling is bulk, evaporation is surface→ The six phase changes
- Deposition ≠ condensation→ The six phase changes
- Dry ice is CO₂, not ice→ Dry ice — solid carbon dioxide
Reference tables (2)
The test: is a new substance formed?4 rows
| Feature | Physical change | Chemical change |
|---|---|---|
| New substance? | No | Yes |
| Molecular composition | Unchanged | Changed |
| Reversible? | Usually yes | Usually no |
| Examples | Melting, boiling, dissolving | Rusting, burning, souring Burning a candle is BOTH: wax melting is physical, vapour burning is chemical. |
Examples: which side is each change on?6 rows
| Event | Change type | Why |
|---|---|---|
| Rusting of iron | Chemical | Iron → iron oxide (new substance) |
| Burning of coal | Chemical | Carbon → CO₂ + ash |
| Souring of milk | Chemical | Bacteria turn lactose into lactic acid Souring of milk LOOKS physical but is chemical — a new acid is formed. |
| Greying of hair (natural) | Chemical | Pigment chemically lost — irreversible Natural greying of hair is a chemical change, not a physical one. |
| Melting of ice | Physical | Still H₂O, just a state change |
| Reaction of acid with base | Chemical | Forms salt + water |
Watch out for (2)
- Physical change keeps the composition→ The test: is a new substance formed?
- Souring and greying are chemical→ Examples: which side is each change on?
Reference tables (2)
Elements, compounds and mixtures6 rows
| Substance | Category | Why |
|---|---|---|
| Tin | Element (pure) | One type of atom — not a mixture |
| Ice | Compound (pure) | Frozen H₂O — not a mixture |
| Sugar | Compound (pure) | C₁₂H₂₂O₁₁ — a pure substance, not a solution |
| Air | Mixture | Mainly N₂ + O₂, variable proportion |
| Brass | Mixture (alloy) | Copper + zinc, variable proportion |
| A compound | Pure substance | Fixed ratio; NOT an impure substance A compound is a PURE substance with fixed composition — the claim 'a compound is an impure substance' is false. |
Homogeneous vs heterogeneous mixtures, and solutions6 rows
| Mixture | Homogeneous or heterogeneous? | Note |
|---|---|---|
| Salt dissolved in water | Homogeneous (a solution) | Uniform, single phase |
| Air | Homogeneous (a solution) | Gases evenly mixed |
| Brass / alloy | Homogeneous (a solution) | Solid solution of metals |
| Sulphur in carbon disulphide | Homogeneous | Sulphur dissolves in CS₂ → true solution Sulphur IS soluble in carbon disulphide, so this is the NON-heterogeneous (homogeneous) one. Sulphur in WATER would be heterogeneous. |
| Milk | Heterogeneous (a colloid) | Fat droplets dispersed in water Milk is heterogeneous, not a true solution — it is a colloid. |
| Sugar and salt crystals | Heterogeneous | Visible separate crystals |
Watch out for (5)
- A compound is pure, not impure→ Elements, compounds and mixtures
- Ice and tin are not mixtures→ Elements, compounds and mixtures
- Milk is heterogeneous, not a solution→ Homogeneous vs heterogeneous mixtures, and solutions
- Sulphur dissolves in CS₂ but not water→ Homogeneous vs heterogeneous mixtures, and solutions
- Divide by the whole solution, not the solvent→ Mass percentage of a solution
Reference tables (2)
True solution, colloid and suspension6 rows
| Property | True solution | Colloid | Suspension |
|---|---|---|---|
| Particle size | < 1 nm | 1–1000 nm | > 1000 nm |
| Appearance | Homogeneous | Heterogeneous | Heterogeneous |
| Tyndall effect | No | Yes | Yes (if not settled) |
| Settle on standing? | No | No (needs centrifuge) | Yes Colloid particles do NOT settle on their own — but centrifugation can separate them. |
| Visible to naked eye? | No | No | Yes Colloidal particles cannot be seen by the naked eye — only suspension particles can. |
| Example | Salt water, CuSO₄ solution | Milk, fog, soap solution | Muddy water, chalk in water |
Soaps, micelles and cleansing action6 rows
| Question asked | Answer |
|---|---|
| What kind of salt is a soap? | Sodium/potassium salt of a long-chain carboxylic acid A soap is a carboxylate (Na/K salt), NOT an ammonium salt — that is the bank's trap statement. |
| Where does dirt collect? | In the centre of the micelle |
| Principle of cleansing | Lowering surface tension (and emulsifying oil) |
| Does soap solution scatter light? | Yes — it is colloidal (Tyndall effect) |
| What forms in hard water? | Insoluble precipitate (scum) with Ca²⁺ and Mg²⁺ |
| Soap with water forms… | A lyotropic liquid crystal Lyotropic = order set by concentration/solvent. Thermotropic = order set by temperature. Soap micelles are lyotropic. |
Watch out for (4)
- A colloid is NOT homogeneous→ True solution, colloid and suspension
- Colloid particles are invisible to the eye→ True solution, colloid and suspension
- Soap is a carboxylate, not an ammonium salt→ Soaps, micelles and cleansing action
- Lyotropic, not thermotropic→ Soaps, micelles and cleansing action
Reference tables (2)
Distillation, fractional distillation and the separating funnel3 rows
| Method | Use it when… | Example |
|---|---|---|
| Distillation | Two miscible liquids, boiling points far apart | Acetone and water; two miscible liquids |
| Fractional distillation | Miscible liquids, boiling points close | Petrol and kerosene; refining petroleum Close boiling points → you need the fractionating column → fractional distillation. |
| Separating funnel | Two immiscible liquids (don't mix) | Water and kerosene oil; oil and water Immiscible = they form separate layers → separating funnel, not distillation. |
Centrifugation, chromatography, sublimation, evaporation and crystallization5 rows
| Method | Separates | Example |
|---|---|---|
| Centrifugation | Suspended solid from liquid (by density, by spinning) | Cream from milk; blood tests Blood tests in diagnostic labs use centrifugation to spin cells from plasma. |
| Chromatography | Components by rate of movement / adsorption | Pigments from plant extract; ink dyes |
| Sublimation | A sublimable solid from a non-sublimable one | Anthracene from salt; camphor from sand Use sublimation only when ONE component sublimes (turns solid → gas). |
| Evaporation | Non-volatile solute from solvent (dry off solvent) | Salt from salt water |
| Crystallization | Pure solute crystals from a hot solution | Pure crystals from a non-volatile solute A non-volatile solid solute can be recovered by EITHER evaporation OR crystallization. |
Watch out for (4)
- Miscible vs immiscible decides the method→ Distillation, fractional distillation and the separating funnel
- Close boiling points need the column→ Distillation, fractional distillation and the separating funnel
- Non-volatile solute → evaporation OR crystallization→ Centrifugation, chromatography, sublimation, evaporation and crystallization
- Sublimation needs a sublimable component→ Centrifugation, chromatography, sublimation, evaporation and crystallization
PYQ weightage by concept
13 concepts · 32 PYQs — where the marks actually sit, so you know what to drill first
PYQ weightage by concept
13 concepts · 32 PYQs — where the marks actually sit, so you know what to drill first
| Concept | PYQs | Share |
|---|---|---|
| Dry ice — solid carbon dioxide | 3 | 9% |
| The six phase changes | 2 | 6% |
| The three states of matter | 1 | 3% |
| Diffusion | 1 | 3% |
| Concept | PYQs | Share |
|---|---|---|
| Examples: which side is each change on? | 3 | 9% |
| The test: is a new substance formed? | 1 | 3% |
| Concept | PYQs | Share |
|---|---|---|
| Elements, compounds and mixtures | 3 | 9% |
| Homogeneous vs heterogeneous mixtures, and solutions | 3 | 9% |
| Mass percentage of a solution | 1 | 3% |
| Concept | PYQs | Share |
|---|---|---|
| True solution, colloid and suspension | 4 | 13% |
| Soaps, micelles and cleansing action | 3 | 9% |
| Concept | PYQs | Share |
|---|---|---|
| Centrifugation, chromatography, sublimation, evaporation and crystallization | 4 | 13% |
| Distillation, fractional distillation and the separating funnel | 3 | 9% |
Test yourself on Matter and Its States
15 past NDA questions from this chapter, timed at 15 minutes and marked the way the exam marks it. You see your score and every answer the moment you finish. Free to start.