Science notes, chapter 5

Matter

Textbook Science Form 1 (DLP), pages 136–161

By the end of this chapter you can

Show that living and non-living things are matter, tell physical and chemical properties apart, and classify materials by density, melting point, boiling point and solubility (5.1)
Use the kinetic theory to compare solids, liquids and gases, compare diffusion rates, and explain changes of state, constant temperature and constant mass (5.2)

5.1Matter in Nature

Matter is anything that has mass and occupies space. Almost everything in nature is matter.

All living things (humans, animals, plants) and non-living things (water, soil, rocks, air) are matter. Things such as light, heat, sound and feelings have no mass and take up no space, so they are not matter.

Proving that things have mass and occupy space

Soil, water and bean sprouts: put each one into a beaker. It fills part of the beaker (occupies space), and the lever balance reading goes up (has mass). So soil (non-living), water (non-living) and bean sprouts (living) are all matter.
Air: two blown-up balloons are balanced on a wooden rod. When one balloon is pricked through a piece of cellophane tape, its air escapes and the rod tilts down on the side of the balloon that is still full. The air had mass. The balloons grew bigger when blown up, so air also occupies space.

Two balloons hanging from a wooden rod; one has cellophane tape and is being pricked — The cellophane tape stops the balloon from bursting, so the air leaks out slowly and the balance is not disturbed by a bang. (Textbook Figure 5.2, p. 140)

An upside-down empty beaker pushed into a basin of water stays almost dry inside. The air trapped in the beaker occupies space, so the water cannot get in.

Physical and chemical properties

Physical properties can be identified with our five senses or with measuring tools. They depend on the type of material the matter is made of.
Chemical properties show up only when a substance changes into a new substance with a different composition. They depend on the reaction that happens.

Boiling water, sugar in coffee, a pan with plastic handle, melting ice cubes — Examples of physical properties. (Textbook Figure 5.3, p. 141)

Physical properties	Chemical properties
Boiling point — water boils at 100 °C	Rusting — iron rusts when exposed to water and air
Melting point — ice melts at 0 °C	Flammability — petrol catches fire easily; paper burns when lit
Solubility — sugar dissolves in coffee
Heat conductivity — a steel pan is a heat conductor; its plastic handle is a heat insulator
Density, colour, shape, hardness

Melting, boiling and dissolving do not make a new substance (melted ice is still water), so they are physical. Burning and rusting make new substances (ash, rust), so they are chemical.

Classify each as a physical or chemical property: (a) an ice cream melts in the sun; (b) an iron key rusts; (c) a medicine tablet dissolves in water.

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(a) Physical (melting). (b) Chemical (rusting makes a new substance). (c) Physical (solubility).

Classifying materials by their characteristics

Materials can be classified by four characteristics: density, melting point, boiling point and solubility. For example, salt is obtained from seawater because water has a much lower boiling point than salt: the water evaporates and salt crystals are left behind.

Density

Density is the mass per unit volume of a material. A material with a lower density floats; a material with a higher density sinks. Oil floats on water because oil is less dense.

A glass with a layer of oil floating on water — Oil floats on water. (Textbook Photograph 5.4, p. 143)

Mixture	Higher density (sinks)	Lower density (floats)
Glycerol and water	Glycerol	Water
Petrol and mercury	Mercury	Petrol
Sand and water	Sand	Water
Oil and cork	Oil	Cork

Melting point and boiling point

Melting point — the temperature at which a substance changes from solid to liquid.
Boiling point — the temperature at which a substance changes from liquid to gas.

Substance	Melting point (°C)	Boiling point (°C)	State at room temperature (about 30 °C)
Water	0	100	Liquid
Alcohol	−117	78	Liquid
Copper	1085	2562	Solid
Oxygen	−218	−183	Gas

Melting and boiling points: textbook Table 5.2, p. 143. Iron melts at 1536 °C.

To find the state at a temperature: below the melting point → solid; between the melting and boiling points → liquid; above the boiling point → gas.

Solubility

Solubility is the ability of a substance (the solute) to dissolve in a given amount of solvent to form a solution.

When you stir sugar into coffee, sugar is the solute, coffee is the solvent and sweet coffee is the solution. Salt and sugar are soluble in water; sand, cooking oil and a glass marble are not.

Use Table 5.2. What is the state of alcohol at 90 °C? Explain.

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Gas — 90 °C is higher than the boiling point of alcohol (78 °C).

5.2Three States of Matter

Matter is made up of tiny, discrete (separate) particles. They are too small to see with the naked eye or even a light microscope; they can only be seen with an electron microscope.

Activity: copper(II) sulphate in water

A few blue copper(II) sulphate crystals are put into 50 ml of water. The blue colour spreads through all the water. When another 50 ml of water is added, the colour spreads again and becomes paler, but it is still blue everywhere.
Conclusion: the crystal is made of many tiny separate particles that spread out between the water particles.

The kinetic theory of matter states that matter is made up of small and discrete particles that are constantly moving and colliding with one another. When heated, the particles move faster; when cooled, they move slower.

Solid, liquid and gas

Matter exists in three states: solid (a ceramic cup), liquid (honey) and gas (vapour from hot tea). Water is the only substance that exists naturally in all three states: ice (solid), water (liquid) and steam (gas).

Arrangement of particles in the three states of matter.

	Solid	Liquid	Gas
Space between particles	Small	Moderate	Large
Arrangement	Very close, in an orderly pattern	Close, not orderly	Very loose, far apart
Movement	Vibrate in fixed positions	Move freely and collide with one another	Move randomly and quickly, colliding with one another
Shape	Fixed shape	Takes the shape of the container	Takes the shape of the container
Volume	Fixed volume	Fixed volume	Fills the whole container
Compressibility	Cannot be compressed	Difficult to compress	Easy to compress

Based on textbook Table 5.3 and Figure 5.8, p. 147.

Wood and iron are used to build bridges because their particles are compactly arranged, giving a fixed shape. A gas can be squeezed into a gas cylinder because there are large spaces between its particles.

Link structure to property: big spaces between particles → gas is compressible; particles fixed in place → solid has a fixed shape.

Did you know? The Sun is neither a solid nor a gas. It is in a fourth state called plasma.

Diffusion

Diffusion is the process in which particles of a substance spread from an area of high concentration to an area of low concentration.

Perfume particles spreading out between air particles from a spray bottle — Perfume particles move randomly between the air particles, so the smell spreads across the room. (Textbook Figure 5.9, p. 148)

Bees use diffusion too: the first bee to attack releases a chemical whose smell diffuses through the air, alerting the swarm from all directions. The smell of cooking spreads through the house in the same way.

Diffusion of copper(II) sulphate in gel and water, and of bromine gas in air — Rate of diffusion in a solid, liquid and gas. (Textbook Figure 5.12, p. 150)

Medium	Observation	Rate of diffusion
Solid (gel)	Gel turns blue after a few days	Lowest
Liquid (water)	Water turns blue after about two hours	Higher than in a solid
Gas (air)	Brown bromine gas fills both gas jars after 15 minutes	Highest

The rate is highest in a gas because the particles are far apart and move fastest and most freely. In a solid the particles are packed closely and only vibrate.

Experiment 5.1 — variables

Hypothesis: the rate of diffusion is low in a solid but high in a liquid.
Manipulated: diffusion medium (gel or water). Responding: rate of diffusion. Constant: temperature.

Changes in the state of matter

Matter changes state when it absorbs or releases heat. Heat changes the kinetic energy of the particles: absorbing heat makes them move faster, releasing heat makes them move slower.

Diagram linking solid, liquid and gas with arrows for melting, freezing, boiling, condensation and sublimation — The effect of heat on matter. (Textbook Figure 5.14, p. 152)

Process	Change	Heat	What the particles do
Melting	Solid → liquid	Absorbed	Gain energy and vibrate faster, overcome the force of attraction and start to move freely at the melting point
Boiling	Liquid → gas	Absorbed	Gain energy and move faster; at the boiling point they break free and move randomly. Happens only at the boiling point, throughout the liquid
Evaporation	Liquid → gas	Absorbed (from surroundings)	Particles at the surface escape slowly. Happens at any temperature
Condensation	Gas → liquid	Released	Lose energy, move slower and closer together
Freezing	Liquid → solid	Released	Lose energy, move slower, and vibrate in fixed positions at the freezing point
Sublimation	Solid → gas, or gas → solid (directly)	Absorbed (solid → gas) / released (gas → solid)	Skip the liquid state

Boiling and evaporation both turn a liquid into a gas, but they are not the same. Boiling happens only at the boiling point and quickly; evaporation happens at any temperature, slowly, and only at the surface.

Temperature and mass during a change of state

When water is heated, its temperature rises until it reaches 100 °C. Then it stays at 100 °C while the water boils, even though heating continues. The same happens at the melting point and the freezing point.

Beaker of 100 ml water heated on a tripod with a thermometer held by a clamp — Measuring the temperature of boiling water. (Textbook Figure 5.15, p. 154)

Why? The heat absorbed is used to overcome the force of attraction between the particles, not to raise the temperature. (When freezing, heat is released as the attractions form.)

Mass stays constant during physical changes. A beaker of ice has the same mass after the ice melts; a beaker of water has the same mass after salt dissolves in it; a metal ball has the same mass before and after it is heated and expands. The number of particles does not change — only their kinetic energy changes.

Worked example

An empty beaker has a mass of 125 g. With ice cubes it has a mass of 173 g. After all the ice melts, the mass is still 173 g.
Mass of ice = 173 − 125 = 48 g = mass of water formed.

Changes of state in daily life

Example	Process
Wet clothes dry on a clothes line	Evaporation
Sweet cream becomes ice cream in a freezer	Freezing
Dry ice keeps ice cream cold; it turns straight into gas	Sublimation
Moth balls in a cupboard become smaller	Sublimation
Dew forms on leaves in the early morning	Condensation
Ice cubes in a drink turn to water	Melting
The surface of a lake freezes in winter (below 0 °C)	Freezing

Why does a bicycle tyre look flatter on a cold morning?

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The air in the tyre releases heat when it is cold. The air particles lose kinetic energy, move slower and come closer together, so the air contracts and the tyre looks flatter.

Summary

Remember	Key fact
Matter	Has mass and occupies space; living and non-living things are matter
Physical vs chemical property	Physical: seen or measured, no new substance (melting point, boiling point, solubility, density, heat conductivity). Chemical: new substance forms (rusting, flammability)
Density	Lower density floats; higher density sinks
Kinetic theory	Matter is made of tiny discrete particles that are always moving and colliding
Particles	Solid: very close, vibrate. Liquid: close, move freely. Gas: far apart, move randomly
Diffusion rate	Gas > liquid > solid
Heat absorbed	Melting, boiling, evaporation, sublimation (solid → gas)
Heat released	Freezing, condensation, sublimation (gas → solid)
During melting, freezing and boiling	Temperature stays constant; mass stays constant during all physical changes