IB MYP Sciences – States and properties of matter Revision Notes

These revision notes cover states and properties of matter for IB MYP Sciences. For full explanations and longer worked examples, start with the study guide.

The notes are aligned to the International Baccalaureate Organization, Middle Years Programme Subject Brief – Sciences, from 2014, which lists states and properties of matter among the topics explored in the MYP sciences on-screen examinations. MYP has no SL/HL levels, and these notes suit MYP years 4 and 5. MYP has no prescribed content list – schools design their own units – so check your school’s unit plan for anything extra your teacher has added.

Course links: IB MYP Sciences hub · printable checklist · practice questions.

Key definitions

• Particle model: all matter is made of tiny particles in constant motion, with forces of attraction between them.
• Temperature: linked to the average kinetic energy of the particles.
• Diffusion: net movement of particles from higher to lower concentration, caused by random motion. Faster when hotter or when particles are lighter.
• Melting point / boiling point: the fixed temperature at which a pure substance melts / boils.
• Density: mass per unit volume.
• Pressure (gas): caused by particles colliding with the container walls.
• Pure substance: a single element or compound, with nothing mixed in.
• Mixture: two or more substances not chemically joined; separable by physical methods.
• Solute / solvent / solution: the solute dissolves in the solvent to make a solution.
• Rf value: distance moved by a spot ÷ distance moved by the solvent front.

The three states at a glance

	Solid	Liquid	Gas
Spacing	Touching	Touching	Far apart
Pattern	Regular	Random	Random
Motion	Vibrate in place	Slide past each other	Fast, random, all directions
Forces	Strong	Medium	Very weak
Shape / volume	Fixed / fixed	Container’s / fixed	Container’s / container’s
Compressible?	No	No	Yes

Changes of state

Name	Change	Energy
Melting	s → l	taken in
Freezing	l → s	given out
Evaporation, boiling	l → g	taken in
Condensation	g → l	given out
Sublimation	s → g	taken in
Deposition	g → s	given out

Why the temperature stays constant during a change of state: the energy supplied overcomes the forces between particles instead of increasing their kinetic energy.

Gas behaviour summary

Change to a fixed amount of gas	Particles	Result
Heated in a sealed rigid container	Move faster; hit walls more often and harder	Pressure rises
Compressed at constant temperature	Less space; more collisions per second on each area of wall	Pressure rises
Heated in a stretchy container (balloon)	Move faster; push the walls outwards	Volume increases
Cooled in a stretchy container	Move slower; fewer, softer collisions	Volume decreases

Keep it qualitative: explain in words, linking particle speed to collisions and then to pressure.

Heating curve reminders

• Sloping part: one state warming; particle kinetic energy rises.
• Flat part: change of state; energy overcomes forces between particles.
• Boiling plateau is longer than melting plateau for the same heater, because particles are separated completely.
• Cooling curve: flat parts at the condensation and freezing points, where energy is given out.

Formulas and relationships

Quantity	Relationship	Units
Density	ρ = m / V	g/cm³ or kg/m³
Mass	m = ρ × V	g or kg
Volume	V = m / ρ	cm³ or m³
Unit conversion	1 g/cm³ = 1000 kg/m³	–
Volume by displacement	V = final reading − initial reading	cm³
Energy from a heater	E = P × t	J (P in W, t in s)
Rf	spot distance / solvent-front distance	no unit

Reference values worth knowing: water 1.00 g/cm³; ice about 0.92 g/cm³; water melts at 0 °C and boils at 100 °C at standard pressure; ethanol boils at 78 °C.

Method in steps

Reading a heating curve

1. Label the sloping parts with the state that is warming (solid, liquid, gas).
2. The lower flat part is the melting point; the higher flat part is the boiling point.
3. Read the temperature of each flat part from the y-axis.
4. Compare the lengths of the flat parts: with a steady heater, a longer plateau means more energy.

Density of an irregular solid

1. Measure its mass on a balance.
2. Part-fill a measuring cylinder with water; read the bottom of the meniscus at eye level.
3. Lower the object in on a thread; read the new level.
4. Volume = difference. Density = mass ÷ volume. Give the unit.

Explaining a gas pressure change

1. Say what happens to particle speed (or the space available).
2. Say what happens to the number of collisions per second, or how hard they hit.
3. Link that to pressure (or volume).

Choosing a separation method

1. Is the solid dissolved or not? Not dissolved → filtration.
2. Want the dissolved solid? → evaporation / crystallisation.
3. Want the liquid? → simple distillation.
4. Two liquids that mix? → fractional distillation.
5. Several coloured substances? → chromatography.

Small worked reminders

• A 12 cm³ sample with mass 32.4 g: ρ = 32.4 / 12 = 2.7 g/cm³.
• 250 cm³ of oil of density 0.80 g/cm³: m = 0.80 × 250 = 200 g.
• Solvent front 6.0 cm, spot 2.4 cm: Rf = 2.4 / 6.0 = 0.40.
• 40 W heater for 90 s: E = 40 × 90 = 3600 J.

Must-know distinctions

• Evaporation vs boiling: evaporation is at the surface, at any temperature, and cools the liquid. Boiling is throughout the liquid, only at the boiling point.
• Melting vs dissolving: melting is one substance changing state because of heat. Dissolving is a solute spreading into a solvent to form a solution.
• Mass vs density: a large log has more mass than a small pebble but a lower density.
• Pure (science) vs pure (everyday): “pure orange juice” is a mixture in science.
• Particles speed up vs particles get bigger: heating makes particles move faster. It doesn’t make them larger.
• Element vs compound vs mixture: compounds have fixed proportions and are chemically joined; mixtures aren’t.
• Simple vs fractional distillation: simple separates a solvent from a dissolved solid; fractional separates liquids with different boiling points.

Concepts link

The brief names energy, movement, transformation and models as examples of related concepts in MYP sciences. In this topic: the particle model is a model; changes of state are transformations; heating transfers energy; temperature describes particle movement. Using these words in extended answers shows you can link ideas beyond one fact. For how the criteria reward that, see criteria in practice revision notes and the assessment revision notes.

Quick self-test

1. Name the change of state from gas directly to solid.
2. A sample has a volume of 12 cm³ and a mass of 32.4 g. Calculate its density.
3. Convert 0.92 g/cm³ to kg/m³.
4. What mass does 250 cm³ of oil of density 0.80 g/cm³ have?
5. A spot moves 2.4 cm and the solvent front 6.0 cm. Calculate Rf.
6. Explain why a sealed balloon shrinks in a freezer.
7. Give two differences between evaporation and boiling.
8. What does an impurity do to the melting point of a solid?
9. Which method gives salt crystals from salt solution?
10. How much energy does a 40 W heater supply in 90 s?
11. A metal has a density of 2.7 g/cm³. What volume does 54 g of it occupy?
12. Why is a chromatography baseline drawn in pencil, not ink?

Answers

1. Deposition.
2. ρ = 32.4 / 12 = 2.7 g/cm³.
3. 0.92 × 1000 = 920 kg/m³.
4. m = 0.80 × 250 = 200 g.
5. Rf = 2.4 / 6.0 = 0.40.
6. The gas particles lose kinetic energy and move more slowly. They hit the inside of the balloon less often and less hard, so the pressure inside falls and the balloon’s volume decreases.
7. Any two: evaporation happens below the boiling point, boiling only at it; evaporation is at the surface, boiling throughout the liquid; evaporation cools the liquid, boiling keeps it at a constant temperature.
8. It lowers the melting point and makes the solid melt over a range of temperatures.
9. Evaporation / crystallisation: heat gently to remove some water, then leave to cool so crystals form.
10. E = 40 × 90 = 3600 J.
11. V = 54 / 2.7 = 20 cm³.
12. Pencil (graphite) doesn’t dissolve in the solvent, so the line won’t run and mix with the spots.

Where marks are usually lost

• Writing that temperature rises during melting or boiling, instead of explaining that it stays constant because energy overcomes forces between particles.
• Saying gas particles “expand” or “get bigger” when heated.
• Explaining pressure without mentioning collisions with the container walls.
• Giving density with no unit, or mixing g with m³.
• Forgetting to subtract the starting volume in a displacement measurement.
• Measuring Rf distances from the bottom edge of the paper rather than from the baseline.
• Suggesting filtration to recover dissolved salt; dissolved particles pass through filter paper.
• Describing evaporation as happening only at 100 °C.
• In a design task, naming “temperature” as a controlled variable but not saying how you would keep it constant.
• Calling a sharp melting point “proof” of a substance’s identity; it shows purity and supports identification when compared with data.

Official syllabus

International Baccalaureate Organization, Middle Years Programme Subject Brief – Sciences, from 2014. Published by the International Baccalaureate Organization.