NDA Chemistry · Teaching notes
Matter and Its States — NDA Chemistry
Matter and Its States is the foundation chapter of NDA Chemistry — 30 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.
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.
Open note
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.
Open note
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).
Open note
Colloids and Suspensions
5 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.
Open note
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).
Open note
PYQ weightage by concept
13 concepts · 30 PYQs — where the marks actually sit, so you know what to drill first
PYQ weightage by concept
13 concepts · 30 PYQs — where the marks actually sit, so you know what to drill first
| Concept | PYQs | Share |
|---|---|---|
| Dry ice — solid carbon dioxide | 3 | 10% |
| The six phase changes | 2 | 7% |
| The three states of matter | 1 | 3% |
| Diffusion | 1 | 3% |
| Concept | PYQs | Share |
|---|---|---|
| Examples: which side is each change on? | 3 | 10% |
| The test: is a new substance formed? | 1 | 3% |
| Concept | PYQs | Share |
|---|---|---|
| Elements, compounds and mixtures | 3 | 10% |
| Homogeneous vs heterogeneous mixtures, and solutions | 3 | 10% |
| Mass percentage of a solution | 1 | 3% |
| Concept | PYQs | Share |
|---|---|---|
| Soaps, micelles and cleansing action | 3 | 10% |
| True solution, colloid and suspension | 2 | 7% |
| Concept | PYQs | Share |
|---|---|---|
| Centrifugation, chromatography, sublimation, evaporation and crystallization | 4 | 13% |
| Distillation, fractional distillation and the separating funnel | 3 | 10% |
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