Chemistry · Lesson 1

Nature of matter & separation techniques

JAMBWAECNECO

What the syllabus asks

JAMB: separation of mixtures and purification of chemical substances; physical and chemical changes; elements, compounds and mixtures; states of matter

WAEC: nature of matter; states of matter and kinetic theory; physical and chemical changes; elements, compounds and mixtures; pure substances and criteria of purity (melting and boiling points); separation techniques: sieving, magnetic separation, decantation, filtration, evaporation, crystallisation, sublimation, simple and fractional distillation, separating funnel, chromatography (Rf), centrifugation

NECO: nature of matter; states of matter and kinetic theory; physical and chemical changes; elements, compounds and mixtures; pure substances and criteria of purity (melting and boiling points); separation techniques: sieving, magnetic separation, decantation, filtration, evaporation, crystallisation, sublimation, simple and fractional distillation, separating funnel, chromatography (Rf), centrifugation

What you will learn

Define matter and describe the three states using the kinetic theory.
Distinguish physical changes from chemical changes with examples.
Distinguish elements, compounds and mixtures and give their differences.
Use melting and boiling points as tests of purity.
Choose and describe the right separation method for any given mixture.
Calculate Rf values and interpret chromatograms.
Plan multi-step separations, e.g. salt from a mixture of sand, salt and iron filings.

Key points

Matter has mass and occupies space; solids, liquids and gases differ in particle spacing, motion and forces.
Kinetic theory: particles are always moving; faster at higher temperature; evidence from diffusion and Brownian motion.
Physical change: no new substance, easily reversed; chemical change: new substance, usually irreversible, heat change.
Elements and compounds are pure; mixtures have variable composition, keep the properties of their parts and are separated physically.
Pure substances melt and boil sharply; impurities lower the m.p. (giving a range) and raise the b.p.
Sieving (size), magnet (magnetism), sublimation (NH₄Cl, I₂, naphthalene).
Decantation, filtration, centrifugation remove insoluble solids from liquids.
Evaporation recovers a stable solute; crystallisation keeps water of crystallisation.
Simple distillation recovers a liquid; fractional distillation separates miscible liquids with close boiling points (crude oil, liquid air).
Separating funnel for immiscible liquids; chromatography for dyes, Rf = spot distance ÷ solvent distance.

Start here: What matter is and its three states

Look around your classroom. The desk, the air you breathe, the water in your bottle, the chalk dust on the board: all of these are matter. Chemistry is the study of matter, what it is made of and how it changes.

Matter is anything that has mass and occupies space (has volume).

Light, heat, sound and shadows are not matter: they have no mass. Air is matter, even though you cannot see it. Blow up a balloon and it takes up space; weigh a pumped football and a flat one, and the pumped ball is slightly heavier.

Matter is made of tiny particles: atoms, molecules or ions. The way these particles are arranged and move gives the three states of matter.

Property	Solid	Liquid	Gas
Shape	Fixed	Takes shape of container	Fills the whole container
Volume	Fixed	Fixed	Not fixed
Particle spacing	Very close, regular	Close, irregular	Far apart
Particle motion	Vibrate about fixed points	Move past one another	Move fast and randomly
Forces between particles	Strongest	Weaker	Very weak
Compressibility	Almost none	Very slight	Easily compressed

The kinetic theory of matter

The kinetic theory says: (1) matter is made of tiny particles; (2) the particles are in constant motion; (3) the higher the temperature, the faster they move (their average kinetic energy is proportional to the absolute temperature). Evidence includes diffusion (the smell of jollof rice spreading from the kitchen to the sitting room) and Brownian motion (pollen grains or smoke particles jiggling randomly because invisible molecules bump into them).

Changes of state

Heating gives particles more energy. Solid → liquid is melting; liquid → gas is boiling or evaporation; gas → liquid is condensation; liquid → solid is freezing; solid → gas directly is sublimation. Evaporation happens at any temperature, from the surface only; boiling happens at a fixed temperature, throughout the liquid. That is why washed clothes on a line in Kano dry without the water ever boiling.

⚠️ Common mistake: saying particles in a solid do not move. They vibrate about fixed positions; they just cannot move from place to place.

Try it yourself. Why can a gas be squeezed into a cooking gas cylinder but a block of wood cannot be squeezed?

Show solution

Gas particles are far apart with large empty spaces between them; the particles in a solid are already packed tightly together.

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Practice questions

1. The best method to separate a mixture of ethanol and water is

fractional distillation
filtration
decantation
sublimation

Show answer

A: fractional distillation
They are miscible with different boiling points.

2. The components of ink can be separated by

evaporation
sieving
magnetism
chromatography

Show answer

D: chromatography
Different dyes travel at different rates.

3. Which of these is a pure substance?

Sea water
Palm wine
Distilled water
Air

Show answer

C: Distilled water
It contains only one substance.

4. Which of these processes produces a new substance?

Grinding chalk
Burning of kerosene
Freezing of water
Dissolving salt

Show answer

B: Burning of kerosene
New substances (CO₂ and H₂O) are formed.

5. Which of these is a compound?

Sodium chloride
Brass
Air
Steel

Show answer

A: Sodium chloride
Its elements are chemically combined in a fixed ratio.

Key words

Matter: Anything that has mass and occupies space.
Element: A substance that cannot be split into simpler substances by chemical means.
Compound: A substance of two or more elements chemically combined in a fixed ratio by mass.
Mixture: Two or more substances physically mixed in any proportion.
Homogeneous mixture: A mixture with uniform composition throughout, e.g. a salt solution.
Heterogeneous mixture: A mixture whose composition is not uniform, e.g. sand in water.
Solute: The substance that dissolves.
Solvent: The substance that does the dissolving.
Filtrate: The clear liquid that passes through a filter.
Residue: The solid left on the filter paper.
Miscible: Liquids that mix completely, e.g. ethanol and water.
Immiscible: Liquids that do not mix and form layers, e.g. kerosene and water.

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