English:Physical and Chemical Properties
Physical and Chemical Properties
Introduction
Everything around you is made of matter. Scientists describe and identify matter by studying its properties. A property is a characteristic of a substance or material. Some properties can be observed or measured without changing what the substance is. Other properties describe how a substance can react and form new substances.
In this aiMOOC, you will learn to distinguish physical properties from chemical properties, measure important physical properties, recognize evidence connected with chemical reactions, and use properties to choose materials for real-world purposes. The course is designed for Grades 7–8 and connects chemistry with laboratory skills, engineering, environmental science, and everyday decision-making.
Learning goals: By the end of the course, you should be able to explain the difference between physical and chemical properties, classify examples, use measurements such as mass and volume to calculate density, connect chemical properties with chemical changes, interpret evidence from simple investigations, and justify why a material is suitable for a particular use.
Properties of Matter
A physical property can be observed or measured without changing the chemical identity of the substance. Examples include color, state of matter, mass, volume, density, melting point, boiling point, solubility, electrical conductivity, thermal conductivity, hardness, and magnetism.
A chemical property describes a substance's ability to undergo a chemical reaction and become one or more new substances. Examples include flammability, reactivity with oxygen, reactivity with acids, reactivity with water, and tendency to corrode or decompose.
A useful question is: Do I need to change the substance into a different substance to observe this property? If the answer is no, the property is physical. If the property describes how the substance reacts or changes chemically, it is chemical.
| Type of property | What it tells you | Examples | Does the substance need to become a new substance? |
|---|---|---|---|
| Physical property | What the substance is like without changing its chemical identity | Density, color, solubility, melting point, conductivity, magnetism | No |
| Chemical property | How the substance can react to form new substances | Flammability, corrosion tendency, reactivity with oxygen or acids | Yes, when the property is tested through a reaction |
Physical Properties in Detail
Physical properties help you describe, compare, identify, and select materials. Some depend on how much material you have. Mass and volume increase when you have more of the same substance. Other properties, such as density or melting point under the same conditions, are useful for comparing samples because they do not simply increase with sample size.
Mass tells you how much matter is in a sample. In school laboratories, mass is commonly measured in grams using a balance.
Volume tells you how much space a sample occupies. The volume of a liquid can be measured with a graduated cylinder. For a regularly shaped solid, you can calculate volume from dimensions. For an irregular solid that does not dissolve or react with water, you can often measure volume by water displacement.
Density
Density compares the mass of a substance with its volume:
Density = mass ÷ volume
For example, if a sample has a mass of 54 g and a volume of 20 cm³, its density is 2.7 g/cm³. A larger sample of the same pure substance can have more mass and more volume while keeping approximately the same density under the same conditions.
Density can help identify materials and explain why some objects float while others sink. Floating also depends on the density of the object compared with the density of the surrounding fluid.
Try this reasoning check: Two blocks are made of the same pure material. One block is twice as large in every dimension. Its mass and volume will be greater, but its density should remain the same if temperature and other conditions are unchanged.
Melting Point and Boiling Point
A melting point is the temperature at which a solid becomes a liquid under specified pressure conditions. A boiling point is the temperature at which a liquid boils under specified pressure conditions. These are physical properties because the chemical identity of the substance does not need to change during the phase change.
A phase change is not automatically a chemical change. Ice melting to liquid water is a physical change because the substance is still water. Water boiling to water vapor is also a physical change.
Solubility
Solubility describes how much of a substance can dissolve in a particular solvent under specified conditions. A substance that dissolves in water has not necessarily undergone a chemical reaction. Dissolving can be a physical process when the dissolved substance retains its chemical identity and can be recovered without chemical reaction.
Solubility can change with temperature, and the pattern is not identical for every substance. A graph can show how solubility changes as temperature changes.
Conductivity, Magnetism, and Hardness
Electrical conductivity describes how well a material allows electric charge to move through it. Metals such as copper are widely used for electrical wiring because copper is a good electrical conductor.
Thermal conductivity describes how well a material transfers thermal energy. A metal spoon usually transfers heat faster than a wooden spoon because the materials have different thermal conductivities.
Magnetism can be tested by observing whether a material is attracted strongly to a magnet. Not all metals are strongly attracted to ordinary magnets.
Hardness describes resistance to scratching or indentation. Hardness is different from strength, stiffness, and toughness, so scientists choose the property that matches the question they are investigating.
Chemical Properties
Chemical properties describe how substances can participate in chemical reactions. You cannot determine a chemical property just by measuring size or color. Instead, the property concerns the ability of the substance to form new substances under particular conditions.
Important examples include:
- Flammability: The ability of a substance to burn in the presence of an oxidizer under suitable conditions.
- Reactivity: The tendency of a substance to react with another substance, such as oxygen, water, or an acid.
- Corrosion: The chemical or electrochemical deterioration of a material through reactions with its environment.
- Chemical stability: The tendency of a substance to resist chemical change under specified conditions.
Chemical properties are always connected to conditions. A material may react rapidly in one environment but slowly in another. Temperature, concentration, surface area, moisture, and the substances present can affect how fast a reaction occurs.
Flammability and Reactivity
Flammability is a chemical property because burning forms new substances. Combustion experiments must only be carried out with appropriate laboratory equipment, teacher supervision, and required safety procedures.
Reactivity with oxygen is another chemical property. Iron can react with oxygen and water in the environment to form rust. Rust has different properties from metallic iron, so rusting is a chemical change.
Evidence During Chemical Changes
When a chemical change occurs, atoms are rearranged into new combinations. The starting substances are called reactants, and the substances formed are called products.
Possible observations that can support the conclusion that a chemical reaction occurred include a gas being produced, a precipitate forming, a lasting unexpected color change, a new odor, or an energy change such as temperature change or light. However, a single observation is not always proof by itself. For example, bubbles can appear during boiling even though boiling is a physical change. Good scientific reasoning considers the substances, the conditions, and several pieces of evidence.
Physical Properties, Chemical Properties, and Changes
A property describes a characteristic or capability of a substance. A change describes what happens to matter. These ideas are related but not identical.
A physical property such as melting point can help predict a physical change such as melting. A chemical property such as flammability can help predict a chemical change such as combustion.
| Situation | Property or change? | Physical or chemical? | Reason |
|---|---|---|---|
| Copper conducts electricity | Property | Physical | Copper can be tested for conductivity without changing its chemical identity. |
| Ice melts | Change | Physical | Water changes state but remains water. |
| Iron can rust in moist air | Property | Chemical | The statement describes iron's ability to react and form new substances. |
| Iron rusts on a wet surface | Change | Chemical | New substances form through chemical reactions. |
| Salt dissolves in water | Change | Usually physical in this context | Salt can be dispersed in water without being treated as a new substance in this school-level example. |
Important idea: Reversibility is not a perfect test for classifying changes. Some physical changes are difficult to reverse, and some chemical reactions can be reversed under suitable conditions. The stronger question is whether new substances with new chemical identities have formed.
Measuring and Investigating Properties
Scientists make observations, take measurements, control variables, and repeat trials. A fair test changes one main variable at a time while keeping other important conditions as constant as possible.
A Safe Density Investigation
You can investigate density using classroom materials.
- Measure the mass of a solid sample with a balance.
- Determine the sample's volume using dimensions or water displacement, depending on its shape and suitability.
- Calculate density by dividing mass by volume.
- Repeat the measurement and compare results.
- Record units and discuss sources of measurement uncertainty.
A good conclusion does more than report a number. It explains whether repeated measurements agree, what may have caused differences, and whether the density supports a claim about the material's identity.
A Safe Conductivity Investigation
With a teacher-approved low-voltage circuit, you can compare materials as electrical conductors. Test materials of similar size when possible, use the same circuit each time, and record whether the bulb or indicator shows current flow. Do not use household mains electricity.
You can then classify the tested materials as better or poorer conductors in your setup. Remember that a simple classroom circuit gives comparative evidence, not a complete measurement of electrical conductivity.
A Corrosion Investigation
A supervised class can compare how environmental conditions affect rusting. Identical iron samples might be placed under different safe conditions, such as dry air, tap water, or salt water. Students can observe changes over several days without tasting, touching unknown residues, or sealing a container in a way that creates pressure.
The investigation connects a chemical property, reactivity with the environment, to visible evidence of a chemical change, corrosion.
Why Properties Matter in Real Life
Engineers and designers choose materials by balancing many properties at once. Electrical wires need high electrical conductivity, but their outer coverings should be electrical insulators. Cooking pans should transfer heat effectively, while handles should reduce heat transfer to your hand. Building materials may need strength, low flammability, corrosion resistance, low density, or weather resistance.
Environmental scientists also study properties. Solubility affects how substances move through water. Reactivity influences how pollutants change in air, soil, and water. Corrosion affects bridges, pipelines, vehicles, and water systems. Understanding properties helps people predict behavior and make safer, more sustainable choices.
Interactive Tasks
Quiz: Test Your Knowledge
Which statement best describes a physical property? (It can be observed or measured without changing chemical identity) (!It always produces a new substance) (!It can only be observed during burning) (!It describes only the color of a material)
Which example is a chemical property? (Flammability) (!Density) (!Mass) (!Melting point)
Why is density useful for comparing samples of the same pure substance? (It can stay the same even when sample size changes) (!It always increases when volume decreases) (!It depends only on color) (!It measures how fast a substance reacts)
Which observation is a physical property of copper? (Electrical conductivity) (!Ability to form rust) (!Ability to burn) (!Reactivity with acid)
Which statement about melting is correct? (Melting is usually a physical change) (!Melting always forms a new substance) (!Melting is a chemical property) (!Melting destroys all particles)
Which statement best describes a chemical property? (It describes how a substance can react to form new substances) (!It describes only the shape of a sample) (!It is always measured in grams) (!It never depends on conditions)
Which is the best evidence that rusting is a chemical change? (New substances form from reactions involving iron) (!The metal becomes wet) (!The metal has mass) (!The sample has a rough shape)
Why are bubbles alone not always proof of a chemical reaction? (Boiling can also produce bubbles during a physical change) (!All gases are liquids) (!Bubbles only occur in solids) (!Chemical reactions never produce gases)
Which property describes how much solute can dissolve under specified conditions? (Solubility) (!Magnetism) (!Hardness) (!Flammability)
Which question best helps distinguish a chemical property from a physical property? (Must the substance chemically change to observe the property) (!Is the sample larger than a pencil) (!Is the object used in a classroom) (!Can the property be written in English)
Memory Game
| Density | Mass per unit volume |
| Solubility | Amount that can dissolve under specified conditions |
| Conductivity | Ability to allow electric charge or heat to move |
| Flammability | Ability to burn under suitable conditions |
| Corrosion | Chemical deterioration through environmental reactions |
| Magnetism | Behavior involving attraction or response to a magnetic field |
Drag and Drop
| Match the correct terms. | Topic |
|---|---|
| Physical property | Observed without changing chemical identity |
| Chemical property | Describes ability to form new substances |
| Density | Mass divided by volume |
| Solubility | Ability to dissolve under specified conditions |
| Flammability | Ability to burn under suitable conditions |
Crossword Puzzle
| Density | What property compares mass with volume? |
| Solubility | What property describes how much can dissolve under specified conditions? |
| Conductivity | What property describes how well a material allows electric charge to move? |
| Flammability | What chemical property describes the ability to burn? |
| Corrosion | What process chemically damages a material through reactions with its environment? |
| Magnetism | What property can be tested with a magnet? |
LearningApps
Cloze Text
Open-Ended Tasks
Easy
- Property Hunt: Find five safe objects at home or in the classroom and record two physical properties of each object without damaging it.
- Material Sorting: Create a poster that sorts common examples into physical properties and chemical properties, then explain two difficult choices.
- Density Storyboard: Draw a four-panel storyboard showing how a student measures mass, measures volume, calculates density, and checks units.
- Science Vocabulary Video: Record a one-minute video explaining physical property, chemical property, and chemical change using your own examples.
Standard
- Conductivity Test: With teacher-approved low-voltage equipment, compare several safe materials as conductors or insulators and present your results in a table.
- Solubility Investigation: Design a fair test comparing how one safe solid dissolves under two teacher-approved conditions and explain which variables you controlled.
- Corrosion Photo Journal: Photograph or sketch safe examples of corrosion in your surroundings and explain what environmental conditions may have contributed.
- Materials Interview: Interview a craftsperson, technician, engineer, cook, or maintenance worker about how material properties influence choices in their work.
Advanced
- Mystery Material Investigation: Use several non-destructive tests to compare unknown classroom samples and write an evidence-based claim about how the samples could be identified.
- Property Data Analysis: Collect reliable data for density, melting point, conductivity, or another property of several materials and create a graph that supports a material-selection decision.
- Corrosion Experiment: With teacher supervision, compare rusting of similar iron samples under safe environmental conditions, document changes over several days, and evaluate sources of uncertainty.
- Engineering Material Challenge: Propose a material for a real product such as a pan handle, bicycle frame, bridge component, or electrical cable and justify the choice using at least four relevant physical or chemical properties.
Learning Assessment
- Classify and Justify: Classify a set of unfamiliar statements as physical properties, chemical properties, physical changes, or chemical changes, and justify every classification with a rule.
- Density Evidence: Analyze repeated mass and volume measurements, calculate densities, identify an outlier, and explain how measurement uncertainty affects the conclusion.
- Reaction Evidence: Given observations from a classroom reaction, decide which observations support the formation of new substances and explain why no single clue should automatically decide the answer.
- Material Selection: Compare candidate materials for an electrical cable, food container, or building component and defend the best choice using several relevant properties.
- Investigation Design: Plan a fair test of solubility, conductivity, or corrosion by identifying the independent variable, dependent variable, controlled variables, safety steps, and expected evidence.
- Transfer Challenge: Explain how understanding physical and chemical properties could help solve a real problem involving recycling, corrosion prevention, product design, or environmental protection.
Evidence of Learning
Knowledge: You can explain physical and chemical properties, give accurate examples, distinguish properties from changes, and connect chemical properties with reactions.
Skills: You can observe carefully, measure mass and volume, calculate density, read property data, control variables, record evidence, compare results, and justify conclusions.
Products: Useful evidence may include a laboratory table, graph, density calculation, investigation plan, annotated photo journal, explanatory poster, short video, or engineering material recommendation.
Scientific reasoning: You can explain why bubbles or color changes are not automatic proof of a chemical reaction, use multiple observations, and distinguish evidence from assumptions.
Transfer: You can apply property knowledge to new materials, environmental situations, technology, construction, cooking, transportation, electrical systems, and safe material selection.
OERs on the Topic
The following open resources can help you review and extend the topic.
Linked Learning Areas