1.3 Properties of Matter: Physical vs Chemical Properties

Chemistry is the study of matter and how it transforms. If you can master how to describe matter and how to tell when it has truly changed versus just looking different, you unlock every chapter that follows. In this complete guide to properties of matter, physical and chemical changes, and separation of mixtures, you will learn how chemists distinguish one substance from another using measurable properties, why intensive properties are your best identification tools in the lab, how to prove a chemical reaction has occurred at the molecular level, and how to choose the exact lab technique to separate any mixture you meet in AP Chemistry, A-Level Chemistry, IB Chemistry HL, College Chemistry 1, and Olympiad exams.

Key Insights

• Physical properties can be measured without changing a substance's identity, while chemical properties describe its ability to become a new substance.
• Intensive properties do not depend on amount and identify substances, while extensive properties depend on amount present.
• All changes of state are physical changes because composition stays the same.
• A chemical change produces chemically different substances with new properties and compositions.
• Mixtures are separated by exploiting differences in physical properties like solubility, boiling point, and adhesion.

Properties of Matter

Every substance has a unique set of properties that lets us distinguish it from every other substance. For example, we can distinguish hydrogen, oxygen, and water from one another because they have different color, odor, density, melting point, boiling point, and reactivity. In chemistry, all of these characteristics fall into two major families.

Physical properties are properties that can be observed and measured without changing the identity and composition of the substance. When you observe a physical property, the substance remains the same substance before and after the observation. Common physical properties include color, odor, density, melting point, boiling point, hardness, electrical conductivity, thermal conductivity, malleability, ductility, viscosity, and solubility.

For example, measuring the melting point of ice at 0°C does not turn water into something else. The water is still water. Observing that copper is reddish-brown and conducts electricity does not change copper into another element.

Chemical properties describe the way a substance may change, or react, to form other substances. A chemical property is only observed when the substance undergoes a change in composition.

The classic example is flammability, the ability of a substance to burn in the presence of oxygen. When gasoline burns, it ceases to be gasoline. When hydrogen gas burns in air, it combines with oxygen to form water. A shiny iron nail that rusts is showing a chemical property: the ability of iron to react with oxygen and water to form iron oxide, a completely different substance with different properties.

Callout Box: Properties vs. Changes - The Core Connection> A property is what a substance has. A change is what a substance does. If observing the trait does not make a new substance, it is a physical property. If you must create a new substance to see the trait, it is a chemical property.

Intensive and Extensive Properties

Chemists make a second, extremely exam-relevant distinction within physical properties.

Intensive properties do not depend on the amount of sample being examined. Temperature, melting point, boiling point, density, color, and hardness are intensive. Whether you have 10 mL or 10 L of water at 25°C, its temperature is still 25°C and its density is still 1.0 g/mL at that temperature. Because intensive properties are independent of sample size, they are particularly useful for identifying substances. In the lab, you never identify an unknown by its mass alone, but you can identify it by its density or melting point.

Extensive properties depend on the amount of sample, with two common examples being mass and volume. Extensive properties relate to the amount of substance present. If you double the amount of material, you double the mass and double the volume. Extensive properties cannot be used alone to identify a substance, because they change with sample size.

Property Type	Depends on Amount?	Examples	Used to Identify Substance?
Intensive	No	Density, melting point, boiling point, temperature, color, odor, specific heat capacity	Yes - excellent for identification
Extensive	Yes	Mass, volume, total energy, length, number of moles	No - changes with sample size

Two clear laboratory glass beakers with water showing intensive vs extensive properties comparison - small and large beaker both at 25.0C with digital thermometers, balance showing mass 150g vs 300g

Pro Tip for Exams:If a question asks you to identify an unknown pure substance from lab data, look immediately for intensive properties in the data table. Students who pick mass or volume as identifiers lose easy marks. On AP and IB, density is often given to disguise that it is intensive.

Exam Trap:Students confuse mass and density. Density is intensive because the ratio mass/volume stays constant even when mass itself changes. Also, temperature is intensive even though it feels like it should increase with more substance. Heating a larger pot of water does not give it a higher temperature, it just requires more heat energy.

This framework also explains the classification of matter you will use constantly. If matter is uniform throughout, it is homogeneous. If it is homogeneous and its composition varies from one sample to another, it is a homogeneous mixture or solution. If it is homogeneous and has a fixed composition that cannot vary, it is a pure substance. Pure substances are either elements, which cannot be separated into simpler substances, or compounds, which can be separated into elements by chemical means.

Consider two real cases. White gold contains gold and a white metal such as palladium. Two samples of white gold can differ in the relative amounts of gold and palladium they contain, but both samples are uniform throughout. Because composition varies, it cannot be a compound. It must be a homogeneous mixture. Aspirin, by contrast, is composed of 60.0% carbon, 4.5% hydrogen, and 35.5% oxygen by mass, regardless of its source. Constant composition that can be separated into simpler elements means it is a compound.

Physical and Chemical Changes

Changes substances undergo are either physical or chemical.

During a physical change, a substance changes its physical appearance but not its composition. That is, it is the same substance before and after the change. The evaporation of water is a physical change. When water evaporates, it changes from the liquid state to the gas state, but it is still composed of water molecules. The chemical formula H₂O does not change. All changes of state, for example from liquid to gas or from liquid to solid, are physical changes. Other physical changes include crushing a can, cutting a wire, dissolving sugar in water, and grinding salt.

At the molecular level, a physical change does not break covalent bonds within molecules. Intermolecular forces may be overcome or formed, but the molecules themselves remain intact. Ice melts because the hydrogen bonds holding H₂O molecules in a rigid lattice are disrupted, but each H2O molecule is still H₂O.

In a chemical change, also called a chemical reaction, a substance is transformed into a chemically different substance. When hydrogen burns in air, for example, it undergoes a chemical change because it combines with oxygen to form water. The starting materials, hydrogen gas H₂ and oxygen gas O₂, cease to exist as those substances, and new matter, water H₂O, with entirely different physical and chemical properties, appears. Burning, rusting, cooking an egg, tarnishing silver, and fizzing when vinegar reacts with baking soda are chemical changes.

Chemical changes are evidenced by several observations you should cite in exams:

1. Evolution of a gas not from boiling
2. Formation of a precipitate, a solid from mixed solutions
3. Permanent color change unrelated to mixing dyes
4. Temperature change without external heating or cooling
5. Emission of light
6. Change in odor

A dramatic example of a chemical change is the reaction of a copper penny with concentrated nitric acid. When the copper contacts nitric acid, the cent is already changed and it is no small change either. A greenish-blue liquid foamed and fumed over the cent and over the table. The air became dark red from nitrogen dioxide gas. The dissolved copper produces a blue-green solution of copper(II) nitrate, while the reddish brown gas produced is nitrogen dioxide. The original copper metal and nitric acid are gone, replaced by new substances. The pain and the stain on hands and trousers that nitric acid causes are also chemical changes: nitric acid acts upon skin proteins and fabrics.

Callout Box: Is Dissolving a Physical or Chemical Change?> Dissolving is usually a physical change. When salt dissolves in water, NaCl still exists as Na+ and Cl- ions that can be recovered by evaporating the water. However, if dissolving is accompanied by a chemical reaction, like dissolving a metal in acid to produce hydrogen gas, it is a chemical change. For AP and A-Level, default to physical unless you see evidence of reaction.

Photorealistic 3D comparison of physical change ice melting retaining H2O composition versus chemical change H2 and O2 gas cylinders burning to form water and copper penny reacting with nitric acid producing blue-green solution and brown gas

Pro Tip for Exams:On FRQs, never say evaporation is a chemical change because water becomes a gas. Examiners specifically test that phase changes are physical. To earn full credit, write: "Composition remains H2O, no new bonds formed within molecules, therefore physical change."

Exam Trap:Students think color change always means chemical change. Mixing blue and yellow paints to make green is a physical change. The color change in the copper and nitric acid experiment is chemical because the blue-green color is from a NEW substance, copper(II) nitrate, not from mixing colors.

Separation of Mixtures

We can separate a mixture into its components by taking advantage of differences in their properties. This is a central skill in the laboratory and a favorite exam topic because each separation method maps directly to a property difference.

Heterogeneous Mixtures

Heterogeneous mixtures are often easier to separate because the components are visibly distinct. For example, a heterogeneous mixture of iron filings and gold filings could be sorted by color, iron is gray and gold is yellow, though this is tedious. A less tedious approach would be to use a magnet to attract the iron filings, leaving the gold ones behind, exploiting the difference in magnetic property.

We can also take advantage of an important chemical difference between these two metals: many acids dissolve iron but not gold. Thus, if we put our mixture into an appropriate acid, the acid would dissolve the iron and the solid gold would be left behind. The two could then be separated by filtration, a process in which a mixture of a solid and a liquid is poured through filter paper. The liquid passes through the paper while the solid remains on the paper. This same principle is used in everyday coffee filters.

Homogeneous Mixtures

An important method of separating the components of a homogeneous mixture is distillation, a process that depends on the different abilities of substances to form gases, that is, differences in volatility and boiling point.

For example, if we boil a solution of salt and water, the water evaporates, forming a gas, and the salt is left behind. The gaseous water can be converted back to a liquid on the walls of a condenser, as shown in laboratory distillation setups. The condenser is a tube cooled by circulating cold water in at the bottom and out at the top. Water vapor condenses on the cold inner surface and drips into the receiving flask as pure water, while pure sodium chloride remains in the original boiling flask.

Distillation is how drinking water is purified from seawater, how crude oil is separated into gasoline and kerosene, and how laboratory solvents are purified. Simple distillation works best when boiling points differ by at least 25-30°C. When boiling points are closer, fractional distillation with a fractionating column is used.

Chromatography

The differing abilities of substances to adhere to the surfaces of solids can also be used to separate mixtures. This ability is the basis of chromatography, literally the writing of colors, a technique that separates substances based on how strongly they stick to a solid versus how easily they dissolve in a mobile liquid or gas phase.

A simple version is paper chromatography, shown by the separation of ink into its components. A drop of black ink is placed near the bottom of a strip of filter paper. The paper is placed upright in a sealed jar with a shallow layer of solvent. As the solvent rises up the paper by capillary action, it carries the ink components with it at different rates. Components that adhere more strongly to the paper move slowly, those that are more soluble in the solvent move faster. The result is separate bands of blue, green, and red dyes that made up the black ink. The same principle powers thin-layer chromatography and column chromatography used in pharmaceutical quality control.

Separation Technique	Property Difference Exploited	Best For	Example
Filtration	Particle size / state	Solid vs liquid heterogeneous mixtures	Sand from water, gold from acid solution
Magnetic Separation	Magnetism	Magnetic vs non-magnetic solids	Iron filings from gold
Distillation	Boiling point / volatility	Homogeneous liquid mixtures or solid dissolved in liquid	Salt water to pure water, ethanol from water
Chromatography	Adhesion to solid surface vs solubility	Similar dissolved substances, dyes, amino acids	Ink dyes, plant pigments, drug testing
Evaporation	Volatility	Recover dissolved solid	Salt from water without collecting water

Three photorealistic lab separation setups side by side - filtration of yellow solid liquid mixture, distillation apparatus with boiling flask salt water and condenser and receiving flask, paper chromatography jar with ink separating into purple blue green bands

Callout Box: Choosing the Right Separation Method - Exam Decision Tree> Ask two questions: 1) Is it heterogeneous or homogeneous? If heterogeneous with solid/liquid, use filtration. If magnetic, use magnet. 2) If homogeneous, does one component have a much lower boiling point? Use distillation. Are they both dissolved colored substances? Use chromatography.

Pro Tip for Exams:When asked to describe how to obtain a pure sample from a mixture, always name the property difference first, then the method, then what happens. For example: "Salt and water have different boiling points, so distill the mixture. Water evaporates at 100°C and is condensed and collected, leaving salt behind." This three-step answer earns full marks on A-Level and IB.

Exam Trap:Students say filtration can separate a solution of salt and water. It cannot, because dissolved Na+ and Cl- ions are smaller than filter paper pores and pass through. Filtration only works for undissolved solids. For dissolved solids, you need evaporation or distillation.

Practice Questions

MCQs (Multiple Choice Questions)

01. Which of the following is an intensive physical property?

1. Mass
2. Volume
3. Density
4. Length

Correct: C - Density is mass/volume, same for any amount of a pure substance at given temperature. Mass, volume, length all depend on amount, so extensive.

02. A copper wire is hammered flat into a sheet. This is a:

1. Chemical change because shape changed
2. Physical change because composition remains Cu
3. Chemical change because conductivity changes
4. Physical change because it becomes a compound

Correct: B - Hammering is malleability, a physical property. Chemical composition remains elemental copper.

03. Which evidence best proves a chemical change occurred?

1. Sugar dissolving in tea
2. Ice melting in your hand
3. Brown gas formed when copper reacts with nitric acid
4. Salt water boiled to dryness

Correct: C - Formation of reddish-brown nitrogen dioxide gas that was not present before indicates new substance formed. Others are physical.

04. Two beakers contain water, 50 mL at 20°C and 200 mL at 20°C. Which statement is true?

1. Both extensive properties are same
2. Temperature is extensive, volume is intensive
3. Temperature is same because intensive, mass is different because extensive
4. Both temperature and volume are intensive

Correct: C - Temperature does not depend on amount, volume and mass do.

05. Which method separates iron filings from sand?

1. Distillation
2. Chromatography
3. Magnet
4. Evaporation

Correct: CIron is magnetic, sand is not, exploiting magnetic property difference.

06. Distillation separates components based on:

1. Difference in particle size
2. Difference in adhesion to paper
3. Difference in ability to form gases / boiling points
4. Difference in magnetism

Correct: C - More volatile component vaporizes first.

07. Flammability is classified as:

1. Extensive physical property
2. Intensive physical property
3. Chemical property
4. Physical change

Correct: C - Flammability describes ability to react with oxygen to form new substances.

08. Black ink is separated into blue and red dyes using paper chromatography. This works because:

1. Dyes have different boiling points
2. Dyes have different magnetic properties
3. Dyes have different adhesion to paper and solubility in solvent
4. Dyes have different densities only

Correct: C - Chromatography relies on partition between stationary and mobile phases.

09. Which is a homogeneous mixture?

1. Iron filings and gold filings mixed
2. Salt water uniform throughout
3. Sand and water
4. Oil and water shaken

Correct: B - Salt water is uniform throughout and variable composition, definition of solution.

10. Aspirin has constant composition 60% C, 4.5% H, 35.5% O. It is classified as:

1. Element because constant composition
2. Homogeneous mixture because uniform
3. Compound because constant composition and can be separated into elements
4. Heterogeneous mixture

Correct: C - Fixed composition plus can be decomposed into simpler substances defines compound.

FRQs (Free Response Questions)

FRQ 1: Identify Properties
A student is given an unknown silver metal. Data: mass 54.0 g, volume 5.14 cm³, density 10.5 g/cm³, melting point 961°C, it does not react with water but reacts with nitric acid to produce a blue solution. Classify each as physical/chemical and intensive/extensive.

Rubric:

• Mass 54.0 g: extensive physical (1 pt)
• Volume 5.14 cm³: extensive physical (1 pt)
• Density 10.5 g/cm³: intensive physical (1 pt) - can identify as silver
• Melting point 961°C: intensive physical (1 pt)
• Does not react with water: chemical property (1 pt) - describes reactivity
• Reacts with nitric acid to produce blue solution: chemical property/chemical change (1 pt)

FRQ 2: Physical vs Chemical Change Analysis
Explain why boiling salt water to obtain pure water and salt involves both a physical change and a separation method, and why filtration would fail to separate salt water.

Rubric:

• Boiling water is physical change, H2O remains H2O, only intermolecular forces broken, phase change (2 pts)
• Salt remains as NaCl, does not decompose at 100°C (1 pt)
• Distillation works because boiling point difference, water volatile, salt non-volatile (2 pts)
• Filtration fails because dissolved ions smaller than filter pores, homogeneous mixture (2 pts)

FRQ 3: Distillation Setup Design
Describe with labeled diagram concept how you would separate a mixture of ethanol (bp 78°C) and water (bp 100°C). Explain where each component ends up.

Rubric:

• Heat mixture in boiling flask, ethanol boils first (2 pts)
• Vapor goes through condenser with cold water inlet lower, outlet upper for efficient condensation (2 pts)
• Ethanol condensed and collected in receiving flask, water remains enriched in original flask initially, simple vs fractional noted (2 pts)
• Mentions boiling point difference as property exploited (1 pt)

FRQ 4: Chromatography Application
A forensic lab uses paper chromatography to determine if two black pens use same ink. Outline procedure and explain how results prove same or different.

Rubric:

• Spot each ink on same paper, place in solvent, solvent rises (2 pts)
• If same, dyes travel same distance, same Rf values, same number of bands and colors (2 pts)
• Different inks show different patterns/Rf, adhesion difference explanation (2 pts)
• Rf = distance traveled by substance / distance traveled by solvent (1 pt)

FRQ 5: Intensive vs Extensive in Identification
You have 10.0 g and 100.0 g samples of the same pure liquid. Which properties will be identical and which will differ? How does this help identify an unknown?

Rubric:

• Identical: density, boiling point, color, odor, temperature at equilibrium - intensive (3 pts)
• Different: mass, volume, total thermal energy - extensive (2 pts)
• Use intensive for identification because independent of amount, compare to known values (2 pts)

Q1: Frequently Asked Questions

What is the difference between physical and chemical properties?

Physical properties can be measured without changing the substance into something new, like density or melting point. Chemical properties describe how a substance reacts to form new substances, like flammability or acidity.

Q2: What is an example of a physical change vs chemical change?

Melting ice into water is a physical change because H2O stays H2O. Burning hydrogen with oxygen to make water is a chemical change because H2 and O2 become H2O, a new substance with different properties.

Q3: Are intensive properties the same for all amounts of a substance?

Yes. Intensive properties like density, boiling point, and color do not depend on amount. A 10 mL sample and a 1 L sample of pure water both have density 1.0 g/mL and boil at 100°C at 1 atm.

Q4: Why is boiling a physical change and not a chemical change?

Boiling only overcomes intermolecular forces to change state. The molecules themselves remain intact. Liquid water and water vapor both have the chemical formula H2O, so no new substance forms.

Q5: What separation method is best for salt and water?

Distillation or evaporation. Since salt water is homogeneous, filtration cannot work. Heating makes water evaporate due to lower boiling point, leaving solid salt behind, and water can be condensed and collected.

Q6: How does chromatography separate mixtures?

Chromatography separates based on differing adhesion to a solid and solubility in a solvent. Components that stick more strongly to the solid move slowly, while those more soluble in the solvent move faster, creating separate bands.

Q7: Is dissolving salt in water a chemical change?

No, it is usually considered a physical change. Salt dissociates into ions that can be recovered unchanged by evaporation. The composition NaCl is still present as ions, no new covalent bonds formed.

Q8: Can filtration separate a homogeneous mixture?

No. Filtration only separates undissolved solids from liquids because dissolved particles are too small for filter paper pores. Use distillation, chromatography, or evaporation for homogeneous mixtures.

Exam Mapping

Concept	A-Level Chemistry	AP Chemistry	IB Chemistry HL	College Chemistry 1	USNCO / IChO
Physical vs Chemical Properties	3.1.1 Atomic structure - identification tests	Big Idea 1 - Properties of matter, lab skills	Topic 1.1 - Physical vs chemical properties	Ch 1 Matter & Measurement	Local section - Matter classification
Intensive vs Extensive Properties	Practical skills - density measurements	Unit 1 - Density calculations, identification	Topic 1.4 - Density as intensive tool	Ch 1.3 - Intensive vs extensive with calculations	Lab practical - use intensive to identify
Physical vs Chemical Changes	3.2.1 Enthalpy, evidence of reaction	Unit 1 - Distinguishing physical vs chemical	Topic 1.1 - Evidence of chemical reaction	Ch 1 - Changes of state	Theory - conservation of mass
Filtration	Required practical - separation	Lab component - separation techniques	Topic 1.1 - Separation techniques	Lab 1 - Filtration techniques	Lab - qualitative analysis
Distillation	3.2.2 Organic separation, crude oil fractionation	Unit 3 - Intermolecular forces & boiling point	Topic 4.2 & 10 - Distillation in organic	Ch 1.3 - Distillation diagram	Lab - purification of liquids
Chromatography	Required practical 4 - chromatography	Unit 3 - Chromatography principles	Topic 21 - Chromatographic methods, Rf	Lab - Paper & TLC chromatography	Lab - Rf calculations, TLC analysis

Conclusion

You now have a complete mastery toolkit for the foundation of all chemistry. You can distinguish physical properties that describe a substance without changing it from chemical properties that reveal its potential to become something new. You know why intensive properties like density and melting point are your go-to identification tools while extensive properties like mass and volume only tell you how much you have. You can confidently classify any change as physical, where composition stays constant and only phase or appearance changes, or chemical, where new substances with new properties appear with tell-tale signs like gas evolution, color change from new product formation, and temperature changes. Most importantly, you can choose the correct separation technique by naming the property difference first: magnetic for magnetism, filtration for particle size, distillation for boiling point, and chromatography for adhesion and solubility.

These principles appear in every AP free response on matter, every A-Level practical assessment, every IB structure and bonding question, and every College Chemistry lab exam. Practice applying them to real lab scenarios, and the rest of chemistry becomes a logical extension.

References

• Chemistry: The Central Science by Brown, LeMay, Bursten, Murphy, Woodward, and Stoltzfus - Latest Edition - Section 1.3 Properties of Matter
• Supplemental laboratory observations on physical and chemical changes and standard separation techniques for undergraduate chemistry