Classification of Matter

What is Matter?

Matter is anything that has mass and occupies space (volume). All physical substances — from air to iron to water — are matter. Matter can be classified in several ways based on its composition and properties.

Pure Substances vs Mixtures

The first and most fundamental classification separates matter into pure substances and mixtures:

Feature	Pure Substance	Mixture
Composition	Fixed, definite	Variable
Melting/Boiling point	Sharp, definite	Range of temperatures
All samples identical?	Yes	No
Can be separated physically?	No	Yes
Examples	Water, gold, NaCl	Salt water, air, sand+iron

Elements

An element is a pure substance that cannot be broken down into simpler substances by ordinary chemical means. Each element is made up of one type of atom. There are approximately 118 known elements, all found in the Periodic Table.

Examples: Hydrogen (H), Oxygen (O), Iron (Fe), Carbon (C), Gold (Au), Copper (Cu)

Compounds

A compound is a pure substance made of two or more elements chemically combined in fixed ratios. Compounds have properties that are completely different from the elements that form them, and can only be broken down by chemical means (not physical).

Example: Water (H₂O) is a compound of hydrogen and oxygen in a 2:1 ratio. It has completely different properties from the explosive gas H₂ or the reactive gas O₂ that make it up.

Classification of Mixtures

Mixtures are classified based on whether their composition is uniform throughout:

Homogeneous mixture (solution): Uniform composition throughout; cannot distinguish components by eye. Examples: salt water, alloys (steel, bronze), air, vinegar. The dissolved substance is the solute; what dissolves it is the solvent.
Heterogeneous mixture: Non-uniform; components are visibly distinct or in different phases. Examples: sand and water, oil and water, salad, granite.

Note: Colloids (e.g. milk, fog) and suspensions (e.g. muddy water) are intermediate — they appear homogeneous but particles are larger than in true solutions.

Separation Techniques

Choose the technique based on the type of mixture and the properties of the components:

Technique	Mixture Type	Principle	Example
Filtration	Solid–liquid (insoluble solid)	Particle size difference	Sand from water
Evaporation	Dissolved solid in liquid	Liquid evaporates, solid remains	Salt from salt water
Simple distillation	Liquids with very different BPs	Differences in boiling point	Water from alcohol
Fractional distillation	Liquids with similar BPs	Repeated vaporisation/condensation	Crude oil refining, air
Crystallisation	Solid dissolved in liquid	Solubility decreases on cooling	Copper sulfate crystals
Chromatography	Dissolved mixtures of solutes	Different affinities for stationary/mobile phase	Ink dyes, amino acids
Magnetic separation	Magnetic + non-magnetic solids	Magnetism	Iron filings from sulfur

Physical vs Chemical Properties

Physical properties: Observable/measurable without changing chemical composition. Examples: colour, state of matter, density, melting point, boiling point, solubility, electrical conductivity.
Chemical properties: Describe how a substance changes its composition during a reaction. Examples: flammability, reactivity with acids, ability to rust, combustibility.

Properties can also be classified as:

Intensive: Do NOT depend on amount of substance (density, melting point, boiling point, colour).
Extensive: DO depend on amount (mass, volume, length, energy).

States of Matter & Density

Matter exists in four states: solid, liquid, gas, and plasma. The kinetic molecular theory explains states in terms of particle arrangement, energy, and movement.

ρ = m / V (density = mass ÷ volume; unit: kg/m³ or g/cm³)

Water: ρ = 1.00 g/cm³ | Gold: ρ = 19.3 g/cm³ | Air: ρ ≈ 0.0013 g/cm³ | Iron: ρ = 7.87 g/cm³

IEB Extension — Colligative Properties & Alloys

Colligative properties depend only on the number of solute particles dissolved, not their identity:

Boiling point elevation: Adding a solute raises the boiling point of the solvent (e.g. antifreeze in a car radiator).
Freezing point depression: Adding a solute lowers the freezing point (e.g. salt on icy roads).

Alloys are solid solutions (homogeneous mixtures of metals). Common examples:

Alloy	Components	Use
Steel	Fe + C (0.2–2%)	Construction, tools
Bronze	Cu + Sn (≈10%)	Statues, bearings
Brass	Cu + Zn (10–45%)	Musical instruments, plumbing
18-carat gold	Au (75%) + Cu/Ag (25%)	Jewellery

Raoult's Law (qualitative): The vapour pressure of a solution is lower than that of the pure solvent. This explains why dissolved solutes raise the boiling point — more energy is needed for solvent molecules to escape from solution.

Matter Classification & Separation Interactive

Mode

How to use

The flowchart shows how to classify any sample of matter. Follow the decision path from top to bottom. Click a node to highlight its path.

Question 1 — Classification

Which of the following is a pure substance?

Correct! Distilled water is a pure compound with a fixed composition (H₂O) and a definite boiling point of 100°C. Air, sea water, and stainless steel are all mixtures.

Air is a mixture of gases. Sea water contains dissolved salts. Stainless steel is an alloy (mixture). Only distilled water (H₂O) is a pure compound with fixed composition.

Question 2 — Elements vs Compounds

Carbon dioxide (CO₂) is best described as:

Correct! CO₂ is a compound — it contains carbon and oxygen atoms chemically bonded together in a fixed 1:2 ratio. It has different properties from pure C or pure O₂.

CO₂ is a compound: two elements (C and O) chemically combined in a fixed ratio (1:2). The components cannot be separated physically, and CO₂ has properties different from its constituent elements.

Question 3 — Separation Technique

A learner needs to separate salt (sodium chloride) from a salt-water solution. Which technique is most appropriate?

Correct! Salt dissolves in water (it's a homogeneous mixture). Evaporation drives off the water as vapour, leaving solid salt behind. Filtration only works for insoluble solids.

Filtration won't work because the salt is dissolved (no solid particles to filter). Evaporation is correct — heat the solution until all the water evaporates, leaving dry salt crystals.

Question 4 — Properties

Which of the following is an intensive property?

Correct! Density (ρ = m/V) is intensive — it does not change with the amount of substance. Whether you have 1 g or 1 kg of gold, the density is always 19.3 g/cm³. Mass, volume, and length all change with amount (extensive).

Density is intensive — it's the ratio of mass to volume, so it stays the same regardless of the amount of substance. Mass, volume, and length are extensive (they depend on how much you have).

Question 5 — Homogeneous vs Heterogeneous

Which of the following is a heterogeneous mixture?

Correct! Granite is heterogeneous — you can see the different mineral crystals (quartz, feldspar, mica) with the naked eye. Brass, wine, and air are homogeneous (uniform composition throughout).

Granite is heterogeneous — distinct mineral grains are visible to the naked eye. Brass (alloy), wine (solution), and air (gas mixture) are all homogeneous — uniform throughout.

Question 6 — Density Calculation

A rectangular block of metal has a mass of 540 g and dimensions 3 cm × 4 cm × 5 cm. What is its density?

Correct! V = 3 × 4 × 5 = 60 cm³. ρ = m/V = 540/60 = 9 g/cm³. This is close to the density of copper (8.96 g/cm³)!

First find the volume: V = 3 × 4 × 5 = 60 cm³. Then ρ = m/V = 540 g ÷ 60 cm³ = 9 g/cm³.

Question 7 — Multi-Step Separation (Analysis)

A learner is given a mixture of iron filings, sand, and common salt (NaCl), and needs to recover all three components separately. Which sequence of steps achieves this?

Correct! Each step must exploit a different property. Iron is the only magnetic component, so remove it first with a magnet (dry, works on the mixed solid). Adding water dissolves only the salt (sand is insoluble), so filtering now separates solid sand from the salt solution. Finally, evaporating the filtrate leaves the dry salt behind. Doing the steps in a different order fails — e.g. a magnet can't pull iron out of a wet slurry as cleanly, and you can't filter salt out of solution because it's dissolved.

Work from the property that is easiest to isolate first: iron filings are magnetic, so a magnet removes them from the dry solid mixture immediately. Then add water — salt dissolves, sand does not — so filtration now separates solid sand from the salt solution. Evaporating the remaining filtrate drives off the water and leaves solid salt behind. Each technique targets one property (magnetism → solubility → volatility of water) in a logical order.

IEB Extension Practice IEB ONLY

IEB Question 1 — Colligative Properties

Why does adding salt to water raise its boiling point, and what term describes this phenomenon?

Correct! Dissolved particles (ions from NaCl) reduce the vapour pressure of the solution (Raoult's Law). Since a lower vapour pressure means more energy is needed to reach atmospheric pressure, the boiling point rises. This is a colligative property — boiling point elevation.

Dissolved solute particles reduce vapour pressure (Raoult's Law). Because vapour pressure is lower, more energy is needed to boil the solution → boiling point elevation. This is a colligative property depending only on the number of particles, not what they are.

IEB Question 2 — Alloy Classification

Bronze is an alloy of copper (Cu) and tin (Sn). How should bronze be classified in terms of the matter classification hierarchy, and why?

Correct! Alloys are solid solutions — homogeneous mixtures where the composition can vary (e.g. bronze can be 85–95% Cu). The metals are not chemically bonded, so bronze is a mixture, not a compound. Its uniform appearance makes it homogeneous.

Bronze is a homogeneous mixture (solid solution). The Cu:Sn ratio is variable, so it's not a compound (which requires fixed ratios). At the atomic level, the metals are uniformly distributed, so it's homogeneous, not heterogeneous.

Complete all questions in your notebook. Where diagrams are required, draw large, neat, labelled diagrams. Show all working for calculations.

Question 1 — Classify a Substance List

Classify each of the following as: element, compound, homogeneous mixture, or heterogeneous mixture. Give a reason for each answer.

(a) Pure copper (b) Table salt (NaCl) (c) Muddy river water (d) Vinegar (e) Oxygen gas (O₂) (f) Concrete (g) Ethanol (C₂H₅OH) (h) Stainless steel

Question 2 — Separation Method Choice & Justification

For each mixture below, state the most suitable separation technique and justify your choice by referring to the property of the components that makes this technique work.

(a) Iron filings mixed with sulfur powder
(b) Alcohol and water (boiling points: ethanol 78°C, water 100°C)
(c) A mixture of blue, red, and yellow food dyes dissolved in water
(d) Sand mixed with water
(e) Copper sulfate crystals dissolved in hot water

Question 3 — Properties Table

Complete the table by identifying each property as physical or chemical, and intensive or extensive:

(a) Flammability of petrol (b) Mass of a rock (c) Boiling point of ethanol (d) Colour of copper (e) Volume of a gas (f) Reactivity of sodium with water (g) Density of gold (h) Length of an iron rod

Question 4 — Density Calculation

A learner pours 150 mL of an unknown liquid into a measuring cylinder. The liquid has a mass of 120 g.
(a) Calculate the density of the liquid in g/mL and in kg/m³.
(b) Is this liquid likely to be water, ethanol (ρ = 0.79 g/mL), or glycerol (ρ = 1.26 g/mL)? Justify your answer.
(c) If this liquid is poured into a beaker of water, will it float or sink? Explain.

Question 5 — Classification Flowchart

Draw a fully labelled classification flowchart for matter. Your flowchart must include: matter → pure substance / mixture → element / compound / homogeneous mixture / heterogeneous mixture. For each final category, provide two examples and state two identifying features. Use questions like "Is the composition uniform?" and "Can it be broken down chemically?" as decision points.

Question 6 — Identifying Metals from Density Data

A learner measures the mass and volume of four unknown metal samples in the lab:

Sample	Mass (g)	Volume (cm³)
A	54.0	20.0
B	44.8	5.00
C	170.1	15.0
D	118.05	15.0

Reference densities: aluminium = 2.70 g/cm³, iron = 7.87 g/cm³, copper = 8.96 g/cm³, lead = 11.34 g/cm³.

(a) Calculate the density of each sample, showing your working.
(b) Using the reference densities, identify the metal in each sample.
(c) Is density an intensive or extensive property? Explain how this data table demonstrates that classification.
(d) If sample A were cut in half, what would happen to its mass, volume, and density? Explain.