Properties and Changes of Materials
KS2SC-KS2-D011
Chemistry domain covering material properties (hardness, solubility, transparency, conductivity, magnetism), solutions, separating mixtures, reversible and irreversible changes. Year 5 only. Builds on KS1 materials and Y4 states of matter.
National Curriculum context
Properties and Changes of Materials at upper KS2 requires pupils to compare and group materials based on physical properties — hardness, solubility, thermal conductivity, response to magnets, transparency — and to investigate mixtures and methods of separating them. Pupils understand that some changes (dissolving, mixing, changes of state) are reversible while others (burning, rusting, reactions involving new substances) are not, and learn to describe the differences using appropriate scientific language. The statutory curriculum requires pupils to investigate whether dissolving, mixing and changes of state produce new materials, providing the foundation for understanding chemical change at KS3.
5
Concepts
3
Clusters
5
Prerequisites
5
With difficulty levels
Lesson Clusters
Compare materials using an extended range of physical properties
introduction CuratedExtended material properties (hardness, solubility, transparency, conductivity) build on KS1 basic properties and provide the investigative framework for all KS2 materials work.
Investigate dissolving and how to separate mixtures
practice CuratedDissolving and separation techniques are practically linked: pupils dissolve a substance and then use evaporation, filtration or sieving to recover it, demonstrating that dissolving is reversible.
Distinguish reversible changes from irreversible chemical changes
practice CuratedReversible and irreversible changes are the conceptual culmination of KS2 materials work; co_teach_hints link C051 to C049 and C050. The distinction between physical and chemical change is foundational for KS3.
Teaching Suggestions (1)
Study units and activities that deliver concepts in this domain.
Separating Mixtures
Science Enquiry Fair TestPedagogical rationale
Fair testing separation methods gives pupils authentic problem-solving experience — they must choose the right technique for each mixture based on the properties of its components. This builds the critical KS2 skill of using scientific knowledge to make predictions and plan investigations, while the reversible/irreversible distinction develops understanding of chemical change.
Prerequisites
Concepts from other domains that pupils should know before this domain.
Concepts (5)
Extended Material Properties
knowledge AI DirectSC-KS2-C047
Comparing and grouping materials based on a wider range of properties: hardness, solubility, transparency, electrical conductivity, thermal conductivity, and response to magnets. Builds on KS1 and Y4 materials knowledge with additional property types.
Teaching guidance
Set up a systematic investigation of material properties using a range of tests: scratch test for hardness (compare wood, metal, plastic, stone), dissolving test for solubility (test sugar, sand, salt, chalk in water), transparency test (classify as transparent, translucent or opaque), thermal conductivity test (wrap identical cups of hot water in different materials and measure cooling rate), electrical conductivity test (insert into a circuit gap), and magnet test. Record results in a property comparison table. Discuss how property knowledge helps engineers and designers choose the right material for each purpose.
Common misconceptions
Children often confuse thermal conductivity with temperature — a metal spoon feels cold not because it is colder than a wooden spoon but because it conducts heat away from your hand faster. Some pupils think that if a material dissolves it has disappeared or been destroyed, rather than understanding it has dispersed into the liquid. Children may believe that hardness and strength are the same thing — glass is hard but brittle, while rubber is soft but strong.
Difficulty levels
Describing observable properties of familiar materials — hard/soft, rough/smooth, transparent/opaque — and sorting materials by one property.
Example task
Sort these materials into two groups: hard and soft. Materials: metal spoon, sponge, rubber band, stone, cotton wool, glass.
Model response: Hard: metal spoon, stone, glass. Soft: sponge, rubber band, cotton wool.
Comparing materials using a wider range of properties — hardness, solubility, transparency, conductivity, magnetism — and testing each property systematically.
Example task
Test these five materials for thermal conductivity. Which material would be best for keeping a drink warm? Explain how you tested.
Model response: I wrapped identical cups of warm water in each material, measured the starting temperature, then measured again after 10 minutes. Results: cotton wool — only 2°C drop. Newspaper — 3°C drop. Plastic bag — 5°C drop. Aluminium foil — 7°C drop. Nothing (control) — 8°C drop. Cotton wool is best for keeping a drink warm because it is the poorest thermal conductor — it traps air and slows heat escaping.
Grouping materials based on multiple properties simultaneously and explaining why specific materials are chosen for specific purposes based on their properties.
Example task
A saucepan has a metal body and a plastic handle. Explain why different materials are used for each part, referring to their properties.
Model response: The metal body is chosen because metals are good thermal conductors — they transfer heat quickly from the hob to the food inside. Metal is also strong, rigid and has a high melting point, so it does not deform or melt at cooking temperatures. The plastic handle is chosen because plastic is a poor thermal conductor (good insulator) — it does not transfer heat to your hand, so you can hold the pan safely. Plastic is also lightweight and can be moulded into a comfortable grip shape. Each part of the saucepan uses a material whose properties match its function perfectly.
Evaluating materials for a design task by considering trade-offs between multiple properties.
Example task
You are designing a lunchbox. It needs to keep food cool, be lightweight, not break when dropped, and be transparent so you can see inside. No single material has all these properties. How would you solve this?
Model response: No single material has all four properties, so I would combine materials. The main body and lid could be transparent plastic — it is lightweight, shatter-resistant, and see-through. But plastic is a poor insulator, so I would line the inside with a thin insulating layer (like foam or a reflective material) to keep food cool. The latch could be metal for strength and durability. I would need to compromise on transparency slightly — the insulating lining would cover some of the inside. This shows that real-world design involves trade-offs: you cannot maximise every property, so you prioritise the most important ones and use combinations of materials to get the best overall result.
Delivery rationale
Science knowledge concept — factual content deliverable with visual representations and adaptive quizzing.
Dissolving and Solutions
knowledge AI FacilitatedSC-KS2-C048
Understanding that some materials dissolve in liquid to form a solution — the solute appears to disappear but is not lost. Understanding that a dissolved substance can be recovered by evaporating the solvent. Dissolving is different from melting.
Teaching guidance
Investigate dissolving by adding salt, sugar, sand and chalk to water, stirring and observing. Weigh the water before and after dissolving salt to show the mass has increased — the salt is still there even though invisible. Investigate factors that affect dissolving rate: temperature, stirring, grain size. Recover a dissolved substance by evaporating the water — leave a saucer of salt solution on a warm windowsill and observe salt crystals forming. Explicitly distinguish dissolving from melting: dissolving requires a solvent (liquid), melting requires heat. Use the terms solute, solvent and solution consistently.
Common misconceptions
The most common misconception is confusing dissolving with melting. Dissolving requires a liquid (solvent); melting requires heat to change a solid to a liquid. Sugar dissolves in water; ice melts in warm air. Children often think that when something dissolves it has gone forever or been destroyed — weighing before and after proves the dissolved substance is still present. Some pupils think stirring makes more solid dissolve rather than simply speeding up the process.
Difficulty levels
Knowing that some materials disappear when stirred into water (dissolve) and that this makes a solution.
Example task
Stir a spoonful of sugar into warm water. What happens? Has the sugar gone?
Model response: The sugar disappears — I cannot see it any more. But the water tastes sweet, so the sugar is still there. It has dissolved in the water to make a sugar solution.
Understanding that dissolving is different from melting, and that dissolved substances can be recovered by evaporating the water.
Example task
What is the difference between sugar dissolving in water and ice melting? How could you get the sugar back?
Model response: Dissolving needs a liquid (solvent) — the sugar mixes into the water and seems to disappear but is still there as tiny invisible particles. Melting needs heat — ice changes from solid to liquid because its temperature rises above 0°C. To get the sugar back, I could evaporate the water by leaving the solution in a warm place. The water turns into vapour and escapes, leaving the sugar behind as crystals.
Investigating factors that affect dissolving rate (temperature, stirring, grain size) and explaining that the total mass of a solution equals the mass of solute plus solvent.
Example task
Design a fair test to find out whether sugar dissolves faster in hot or cold water. What will you keep the same?
Model response: I will measure the time for one level teaspoon of sugar to dissolve completely in 200ml of water at two different temperatures: cold (room temperature, about 20°C) and hot (about 60°C). I will keep the same: amount of sugar, amount of water, type of sugar, and I will stir both at the same speed. I predict the sugar will dissolve faster in hot water because the water particles move faster when heated, so they mix with and break apart the sugar particles more quickly. I will repeat each test three times and calculate an average for reliability.
Applying dissolving knowledge to explain real-world phenomena and understanding saturation — that there is a limit to how much solute can dissolve.
Example task
You keep adding salt to a glass of water and stirring. Eventually, no more salt dissolves and it sits at the bottom. Explain what has happened and what you could do to dissolve more.
Model response: The solution has become saturated — the water has dissolved as much salt as it can hold at this temperature. The water particles are already surrounded by as many salt particles as they can accommodate, so additional salt cannot dissolve and sinks to the bottom. To dissolve more salt, I could: (1) heat the water — warmer water can usually dissolve more solute because the particles move faster and have more energy to interact with the salt; (2) add more water — a larger volume of solvent can dissolve more solute. This concept of saturation explains why the Dead Sea is so salty — the water is so saturated with dissolved minerals that salt crystallises along the shore.
Delivery rationale
Science fair test concept — requires physical apparatus and variable control, but AI can structure the enquiry sequence.
Separating Mixtures
knowledge AI DirectSC-KS2-C049
Understanding that mixtures of solids, liquids and gases can be separated using various techniques: filtering (remove insoluble solids from liquids), sieving (separate solids by particle size), evaporating (recover dissolved solids). Technique chosen depends on properties of components.
Teaching guidance
Demonstrate each separation technique practically: use sieving to separate rice from flour; filtering to separate sand from water (using filter paper and funnel); evaporating to recover salt from salt water (using an evaporating dish over a water bath). Discuss which technique is appropriate for which mixture and why — sieving separates by particle size, filtering separates insoluble solids from liquids, evaporation separates dissolved solids from liquids. Challenge pupils with mystery mixtures to separate (e.g., salt, sand and iron filings — use magnet, then dissolve salt in water and filter, then evaporate). Link separation techniques to real-world applications: water purification, mining, recycling.
Common misconceptions
Children often think that filtering can separate dissolved substances from water — it cannot; only evaporation or distillation works for solutions. Some pupils confuse sieving with filtering, not recognising the difference in particle size involved. Children may believe that once mixed, substances can never be separated, rather than understanding that different properties allow different separation methods.
Difficulty levels
Knowing that you can separate some mixtures, such as using a sieve to separate large pieces from small ones.
Example task
You have a mixture of rice and flour. How can you separate them?
Model response: I can use a sieve. The flour falls through the tiny holes but the rice grains are too big and stay on top. So the sieve separates the big pieces from the small pieces.
Using filtering to separate insoluble solids from liquids and evaporation to recover dissolved solids, choosing the correct method for each mixture.
Example task
You have muddy water. How would you get clean water from it?
Model response: I would filter the muddy water by pouring it through filter paper in a funnel. The soil particles are too big to pass through the tiny holes in the filter paper, so they are trapped. Clean water passes through into a container below. Filtering works because the soil does not dissolve in water — it is an insoluble solid mixed in the liquid.
Selecting the appropriate separation technique for different mixtures and explaining why each technique works based on the properties of the components.
Example task
How would you separate a mixture of sand and salt?
Model response: This requires a multi-step process because sand and salt have different properties. Step 1: Add water and stir — the salt dissolves but the sand does not (using the property of solubility). Step 2: Filter the mixture — the sand is trapped by the filter paper and the salt solution passes through (using particle size). Step 3: Evaporate the water from the salt solution — the water turns to vapour and the salt is left behind as crystals (using the difference in boiling points). Each step uses a different property to separate the components.
Applying separation knowledge to unfamiliar or multi-step problems and evaluating the effectiveness of different separation strategies.
Example task
A scientist has a mixture of iron filings, sand, salt and water. Plan a method to recover all four components separately. Explain the order and why.
Model response: Step 1: Use a magnet to remove the iron filings (using the magnetic property — iron is magnetic, the others are not). Step 2: Filter the remaining mixture — sand is trapped by the filter paper, and salt water passes through (using insolubility of sand). Step 3: Evaporate the water gently — water turns to vapour and can be collected by condensation, while salt crystals are left behind. The order matters because the magnet must be used first while the iron filings are accessible. Filtering must come before evaporation because we need to remove the sand before recovering the salt. Each step exploits a different property: magnetism, solubility, boiling point. The scientist recovers all four components: iron filings, sand, salt and water.
Delivery rationale
Science knowledge concept — factual content deliverable with visual representations and adaptive quizzing.
Reversible Changes
knowledge AI FacilitatedSC-KS2-C050
Understanding that some material changes are reversible — the original materials can be recovered. Examples: dissolving, mixing, melting, freezing, evaporation, condensation. The material is changed in form but not in substance.
Teaching guidance
Investigate a range of reversible changes: melt chocolate and let it re-solidify; dissolve salt and evaporate to recover it; freeze water and melt the ice. Create a concept map linking all reversible changes, emphasising that the original materials can always be recovered and no new substance is formed. Compare each reversible change with an equivalent irreversible change — melting chocolate (reversible) versus burning toast (irreversible). Use the criterion 'Can we get the original material back?' as the key test. Discuss everyday examples: drying wet clothes (reversible evaporation of water), recycling metals by melting and reshaping.
Common misconceptions
Children often think that all changes caused by heating are irreversible, not recognising that melting and evaporation are reversible. Some pupils believe dissolving is irreversible because they cannot see the solid, when in fact evaporation will recover it. Children may confuse reversible changes with the idea of 'undoing' something — reversibility means the original materials can be recovered, not that the exact same object is restored.
Difficulty levels
Knowing that some changes can be undone — for example, ice can melt and then be frozen again.
Example task
If you melt a chocolate bar, can you change it back into solid chocolate?
Model response: Yes. If you put the melted chocolate in a mould and let it cool down, it goes hard again and becomes solid chocolate. You can change it back.
Understanding that reversible changes include dissolving, melting, freezing, evaporation and condensation, and that the original materials can be recovered.
Example task
Give three examples of reversible changes and explain how you would reverse each one.
Model response: 1. Melting ice — reverse it by cooling (freezing) the water back to ice. 2. Dissolving salt in water — reverse it by evaporating the water to recover the salt. 3. Evaporation of water — reverse it by cooling the water vapour so it condenses back to liquid water. In each case, no new substance is formed — the original material is just in a different state or mixed in, and can be recovered.
Explaining what makes a change reversible — no new substance is formed — and distinguishing reversible from irreversible changes using this criterion.
Example task
Classify these changes as reversible or irreversible: melting butter, baking a cake, dissolving sugar, burning wood, freezing juice. Explain the rule you used.
Model response: Reversible: melting butter (cool it to solidify again), dissolving sugar (evaporate to get sugar back), freezing juice (melt it back to liquid). Irreversible: baking a cake (you cannot unbake it — the raw ingredients have chemically changed), burning wood (ash and gases are formed — you cannot get the wood back). The rule: if no new substance is formed and you can get the original materials back, the change is reversible. If new substances with different properties are formed, the change is irreversible.
Evaluating ambiguous cases and explaining why some changes are harder to classify than others.
Example task
Is mixing paint colours reversible or irreversible? Is crumpling paper? These are tricky cases — explain your thinking.
Model response: Mixing paint: This is debatable. No new chemical substance is formed — the pigments are just physically mixed. In theory, you could separate them (centrifuge, chromatography) but in practice, it is very difficult. Scientifically, it is a physical change (reversible in principle) but practically irreversible for us. Crumpling paper: Reversible in the sense that no new substance is formed — you can flatten the paper again. But it will not return to its exact original condition (creases remain). These tricky cases show that reversible/irreversible is not always black and white. The key scientific test remains: has a new substance been formed? If yes, it is irreversible. If no, it is reversible even if full recovery is difficult in practice.
Delivery rationale
Science fair test concept — requires physical apparatus and variable control, but AI can structure the enquiry sequence.
Irreversible Changes
knowledge AI FacilitatedSC-KS2-C051
Understanding that some changes result in the formation of new materials and are not easily reversed. Examples: burning, rusting, acid reacting with bicarbonate of soda, cooking. New substances are formed that cannot easily be changed back.
Teaching guidance
Demonstrate irreversible changes safely: burn a piece of paper or candle (adult-supervised), mix vinegar with bicarbonate of soda to observe gas production, cook an egg, and observe rusting of iron wool in damp conditions over several days. In each case, discuss what evidence shows a new substance has formed — change in colour, production of gas, change in temperature, production of light or smoke. Contrast with reversible changes done in parallel: melt ice alongside burning a candle. Emphasise that irreversible changes produce new materials with different properties. Introduce the term 'chemical change' informally.
Common misconceptions
Children often struggle to distinguish irreversible from reversible changes. A useful test is: 'Has a new substance been formed with different properties?' Cooking an egg is irreversible — you cannot uncook it because the proteins have permanently changed. Some pupils think burning makes things disappear rather than producing new substances (ash, gases, smoke). Children may not recognise rusting as a chemical change because it happens slowly.
Difficulty levels
Knowing that some changes cannot be undone — for example, you cannot turn a cooked egg back into a raw egg.
Example task
Can you turn toast back into bread? Why or why not?
Model response: No. The bread has changed colour and texture from the heat. It has become something different and you cannot change it back to normal bread.
Identifying signs that a new substance has been formed: colour change, gas production, temperature change, or a substance with different properties from the starting materials.
Example task
When you mix vinegar and bicarbonate of soda, it fizzes. Is this a reversible or irreversible change? How do you know?
Model response: It is irreversible. I know because: the fizzing is a gas being produced (carbon dioxide) — this is a new substance. The remaining liquid is different from both the vinegar and the bicarbonate. New substances have been formed that cannot easily be turned back into vinegar and bicarbonate of soda. Signs of an irreversible change include gas production, colour change, and temperature change.
Explaining multiple examples of irreversible changes, identifying evidence that new materials have formed, and contrasting with reversible changes.
Example task
Compare what happens when you (a) melt wax and (b) burn wax. Which is reversible? What evidence tells you?
Model response: (a) Melting wax is reversible — the wax changes from solid to liquid when heated and back to solid when cooled. No new substance is formed; it is still wax throughout. (b) Burning wax is irreversible — the wax reacts with oxygen in the air to produce carbon dioxide gas and water vapour (and heat and light). These are completely new substances with different properties from wax. You cannot collect the gas and smoke and turn them back into a candle. Evidence for irreversibility: light and heat given off, gas produced, soot (carbon) deposited, the wax is permanently consumed. Same material, two different processes — one reversible, one irreversible.
Explaining irreversible changes in terms of new substances being formed with different properties, and recognising useful irreversible changes in everyday life.
Example task
Give three examples of useful irreversible changes that we rely on in everyday life. Why is it helpful that these changes cannot be reversed?
Model response: 1. Cooking food — heat causes chemical changes that make food digestible, safe and tasty. If cooking were reversible, our meals would revert to raw ingredients in our stomachs. 2. Setting concrete — cement mixed with water undergoes an irreversible chemical reaction that forms a hard solid. This is useful because buildings need to stay solid permanently. If it were reversible, buildings would dissolve in rain. 3. Vulcanising rubber — heating rubber with sulphur permanently changes it from weak and sticky to strong and elastic. Car tyres must stay tough. Not all irreversible changes are bad — many are essential. The key is that irreversible changes produce new substances with properties we want: hardness, stability, safety.
Delivery rationale
Science observation concept — requires sustained observation of real phenomena with adult support.