Introduction to the particulate nature of matter — IB Chemistry HL Revision Notes & Topical Questions

Section 1 of 27Elements and compounds

Element

Element a substance made from one kind of atom that cannot be chemically broken down into simpler substances.

Compound

Compound a substance made from two or more elements chemically bonded in a fixed ratio.

• Atoms combine in fixed ratios that give them full outer shells of electrons.
• Properties of a compound differ greatly from those of its elements.
• Sodium (reactive metal) and chlorine (toxic gas) form harmless sodium chloride.

Reactions

• Reactions elements take part in chemical reactions, which usually involve an energy change.

Section 2 of 27Mixtures

Mixtures

Mixture

• Mixture contains more than one element or compound in no fixed ratio, with the components not chemically combined.

Properties kept

• Properties kept each component keeps the characteristic properties it has when pure.
• Nitrogen and oxygen in air keep their own properties, and oxygen still supports combustion.

No fixed melting or boiling point

• No fixed melting or boiling point a mixture melts or boils over a temperature range.

Homogeneous mixture

• Homogeneous mixture uniform composition and properties throughout.
• Examples are air and bronze (an alloy).

Heterogeneous mixture

• Heterogeneous mixture non-uniform composition, so properties differ through the sample.
• Examples are concrete and orange juice with pulp.
• The separate components can often be seen.

Section 3 of 27Separating solids: solvation, filtration, crystallisation

Basis

• Basis every method relies on a difference in a physical property such as solubility or boiling point.

Solvation

Solvation dissolving of a solute because solvent particles surround and attract the solute particles.

• In water it is called hydration.
• The solvent is chosen to dissolve only the desired component, for example water dissolves salt but not sand.

Filtration

• Filtration separates an insoluble solid from a liquid or solution using filter paper.
• The filtrate passes through and the residue stays on the paper because its particles are too large for the pores.
• Vacuum filtration suits very fine solids that clog filter paper.
• Centrifugation can separate particles that are too small or dense for filtration.

Crystallisation

• Crystallisation separates a dissolved solid that is more soluble in hot solvent than cold.
• Do not boil to dryness, because this may prevent crystal formation.
• Cooling slowly lets larger crystals grow.

1

Heat the solution gently to evaporate some solvent.

2

Cool until saturated, testing with a cold glass rod on which crystals form.

3

Leave the saturated solution to cool slowly so that crystals form.

4

Filter to collect the crystals.

5

Wash with distilled water and dry on filter paper.

Section 4 of 27Recrystallisation

Purpose

• Purpose purifies an impure solid by dissolving it in hot solvent and letting it crystallise as the solution cools.

Minimum solvent

• Minimum solvent use the minimum amount of hot solvent to avoid loss of product.

Basis

• Basis it separates by differential solubility in hot and cold solvent.

Büchner filtration

• Büchner filtration under reduced pressure it is faster and more effective than gravity filtration.

1

Add the minimum amount of hot solvent to the impure solid until it dissolves.

2

Perform hot filtration if solid impurities remain.

3

Cool slowly to room temperature so crystals form as solubility decreases.

4

Collect the crystals by filtration, preferably with Büchner apparatus.

5

Wash the crystals with fresh cold solvent to remove soluble impurities.

6

Dry the crystals on filter paper.

Section 5 of 27Distillation

Simple distillation

• Simple distillation separates a solvent from a solute, or a liquid from a mixture, using a difference in boiling point.
• It suits a collected liquid with a much lower boiling point than the other components.
• The distillate is collected and the solute is left in the flask.

Fractional distillation

• Fractional distillation separates miscible liquids with similar boiling points using a fractionating column.
• Ethanol (78 °C) is distilled from water (100 °C) by heating to 78 °C.
• Crude oil is separated this way industrially.
• Use an electric heater when flammable liquids are present.

Separating funnel

• Separating funnel separates immiscible liquids of different densities, such as oil and water.

1

Heat the mixture in a round-bottomed flask.

2

The liquid with the lowest boiling point evaporates first.

3

Vapour passes up the fractionating column, which improves separation.

4

Vapour condenses in the condenser and the distillate is collected.

5

As the temperature rises the next component distils and is collected in turn.

Section 6 of 27Chromatography and magnetic separation

Chromatography and magnetic separation

Chromatography

• Chromatography separates dissolved substances using differences in solubility and in adsorption to the paper.

Soluble components

• Soluble components those more soluble in the solvent travel further.

Adsorbed components

• Adsorbed components those more strongly adsorbed to the paper move more slowly.

Chromatogram

• Chromatogram the pattern of spots showing the different components.

Magnetic separation

• Magnetic separation uses a magnet when one component is magnetic, for example iron mixed with sulfur.

1

Draw a pencil line near the bottom of the paper, because pencil does not dissolve in the solvent.

2

Place small spots of the sample on the line.

3

Suspend the paper in a shallow layer of solvent with the spots above the solvent level.

4

Let the solvent rise by capillary action, carrying components at different rates.

5

Dry the paper and observe the separated spots.

Section 7 of 27States of matter

Property	Solid	Liquid	Gas
Shape and volume	Fixed shape and volume	Fixed volume, takes shape of container	No fixed shape or volume
Arrangement	Close-packed, regular, ordered	Close together, random	Widely spaced, random
Motion	Vibrate in place	Slide past one another	Fast, random, in all directions
Density	High	Medium	Very low
Compressibility	Not compressible	Almost not compressible	Easily compressed
Particle energy	Lowest	Intermediate	Highest

Kinetic molecular theory

• Kinetic molecular theory explains the properties of solids, liquids and gases in terms of energy, arrangement and motion of particles.

Pressure

• Pressure particle motion in a gas causes collisions that generate pressure.

Section 8 of 27Changes of state

Changes of state

Physical changes

• Physical changes they are reversible, involve energy transfer and do not change the chemical identity of the substance.

Melting

• Melting solid to liquid.

Freezing

• Freezing liquid to solid.

Condensation

• Condensation gas to liquid.

Sublimation

• Sublimation solid to gas.

Deposition

• Deposition gas to solid.

Vaporisation

• Vaporisation liquid to gas.
• Boiling occurs throughout the liquid at a specific temperature, when vapour pressure equals external pressure.
• Evaporation occurs only at the surface, at temperatures below the boiling point.

Endothermic changes

• Endothermic changes melting, vaporisation and sublimation need energy to overcome intermolecular forces.

Exothermic changes

• Exothermic changes freezing, condensation and deposition release energy as particles come closer.

• State symbols
  • (s) solid, (l) liquid, (g) gas, (aq) aqueous;
    • marks are often given for them in ionisation energy, lattice enthalpy (HL) and enthalpy of formation (HL).

Section 9 of 27Temperature, heating curves and Kelvin

Temperature

• Temperature a measure of the average kinetic energy of the particles;
  • it is directly proportional to temperature in kelvin.

Same temperature

• Same temperature all gases have the same average kinetic energy, but lighter particles move faster.

Heating curve

• Heating curve temperature rises while a single state is heated.
• Particles gain kinetic energy.
• During melting and boiling the temperature stays constant.
• The energy goes into overcoming intermolecular forces, not into kinetic energy.

Gas region

• Gas region the gas has the highest average kinetic energy and its temperature rises again after boiling.

Kelvin scale

Kelvin scale the absolute scale, with steps of the same size as °C (1 K = 1 °C).

Absolute zero

• 0 K, where particles have no kinetic energy.

Conversion

• T(K) = T(°C) + 273.15 and T(°C) = T(K) − 273.15.

Section 10 of 27Choosing a separation method

Basis

• Basis every separation exploits a difference in a physical property of the components.

Properties used

• Properties used boiling point, solubility, magnetism or density.

Section 11 of 27Simple distillation

Use

• Use separates a solvent from a solute, or a pure liquid from a mixture, using a difference in boiling point.

Suitable when

• Suitable when the liquid collected has a much lower boiling point than the other components, for example water from salt solution.

Result

• Result the solute stays in the flask and the distillate is collected in a clean beaker.

1

Heat the solution in a round-bottomed flask.

2

The lowest-boiling liquid evaporates first.

3

The vapour passes into the condenser and condenses.

4

The distillate is collected in a clean beaker.

Section 12 of 27Fractional distillation

Use

• Use separates two or more miscible liquids with similar boiling points, such as ethanol and water or crude oil in industry.

Fractionating column

• Fractionating column vapour passing up it gives better separation before reaching the condenser.

Collection

• Collection as the temperature rises the next component evaporates and is collected in turn.

Ethanol and water

• Ethanol and water heat to 78 °C to distil off the ethanol.
  • (water boils at 100 °C)

Safety

• Safety use an electric heater when flammable liquids are present.

Crude oil

• Crude oil it cannot be distilled safely in school labs, so synthetic crude oil is used for demonstrations.

Section 13 of 27Paper chromatography

Use

• Use separates dissolved substances using differences in solubility in the solvent and adsorption to the paper, for example dyes in ink or plant pigments.

More soluble

• More soluble substances travel further.

More strongly adsorbed

• More strongly adsorbed substances move more slowly.

Chromatogram

• Chromatogram the pattern of spots showing the components.

1

Draw a pencil line near the bottom of the paper, because pencil does not dissolve in the solvent.

2

Place small spots of the sample on the line.

3

Suspend the paper in a shallow layer of solvent with the spots above the solvent level.

4

The solvent rises by capillary action, carrying components at different rates.

5

Dry the paper and observe the chromatogram.

Section 14 of 27Matching technique to property

Technique	Property used	Separates
Filtration	Solubility (insoluble solid and liquid)	Sand from salt solution
Crystallisation	Solubility falls as temperature falls	Copper(II) sulfate crystals from solution
Recrystallisation	Solubility in hot and cold solvent	Purifies an impure solid
Simple distillation	Boiling point of solvent and solute	Water from salt solution
Fractional distillation	Boiling points of miscible liquids	Ethanol and water, gases in air
Chromatography	Solubility and adsorption	Dyes in ink or food colouring
Magnetic separation	Magnetic properties	Iron from sulfur

Section 15 of 27Kinetic molecular theory

1Theory

• Theory explains the properties of solids, liquids and gases by the energy, arrangement and motion of their particles.

2Pressure

• Pressure in a gas, particle collisions create pressure.

3Energy flow

• Energy flow state diagrams show spacing, order and energy, with energy increasing from solid to gas.

Section 16 of 27The three states

Property	Solid	Liquid	Gas
Shape and volume	Fixed shape and volume	Fixed volume, shape of container	No fixed shape or volume
Arrangement	Closely packed, regular, ordered	Close but random	Widely spaced, random
Motion	Vibrate in place only	Slide past one another so they flow	Fast and random in all directions
Density	High	Medium	Very low
Compressibility	Very low	Very low	Easily compressed
Particle energy	Lowest	Higher than solid	Highest

Section 17 of 27More from the specification

1

Elements, compounds, and separation steps

• Pure elements contain only one type of atom,
• whereas chemical compounds consist of two or more elements chemically bonded in fixed ratios;
  • physical separation steps such as using filter paper separate heterogeneous mixtures without breaking chemical bonds.

2

States of matter and intermolecular forces

• Solids, liquids,
• and gases differ in particle arrangement and mobility governed by intermolecular forces,
• which are strongest in solids and negligible in ideal gases.

3

Temperature on the Kelvin scale

• Absolute temperature measured in Kelvin is directly proportional to the average kinetic energy of particles in a substance (T (K) = theta (deg C) + 273.15),
• meaning at 0 K particles possess minimal kinetic energy.

4

Phase changes and constant temperature

• During state changes, thermal energy is used to overcome intermolecular forces rather than accelerate particles,
  • (melting, boiling)
• so the temperature remains constant while latent heat is absorbed.

5

Elements, compounds, and separation steps

• Pure elements contain only one type of atom,
• whereas chemical compounds consist of two or more elements chemically bonded in fixed ratios;
  • physical separation steps such as using filter paper separate heterogeneous mixtures without breaking chemical bonds.

6

States of matter and intermolecular forces

• Solids, liquids,
• and gases differ in particle arrangement and mobility governed by intermolecular forces,
• which are strongest in solids and negligible in ideal gases.

7

Temperature on the Kelvin scale

• Absolute temperature measured in Kelvin is directly proportional to the average kinetic energy of particles in a substance (T (K) = theta (deg C) + 273.15),
• meaning at 0 K particles possess minimal kinetic energy.

8

Phase changes and constant temperature

• During state changes, thermal energy is used to overcome intermolecular forces rather than accelerate particles,
  • (melting, boiling)
• so the temperature remains constant while latent heat is absorbed.

9

Element

• A substance made of only one type of atom.

10

Compound

• Two or more elements chemically combined in a fixed ratio.

11

Kelvin

• The SI unit of temperature.

12

Intermolecular forces

• Weak attractions between separate molecules, overcome on melting or boiling.

Section 18 of 27Changes of state

• Nature
  • state changes are physical and reversible and involve energy transfer without changing chemical identity.

Change	From → to	Energy
Melting	solid → liquid	Endothermic
Freezing	liquid → solid	Exothermic
Vaporisation	liquid → gas	Endothermic
Condensation	gas → liquid	Exothermic
Sublimation	solid → gas	Endothermic
Deposition	gas → solid	Exothermic

Section 19 of 27Boiling, evaporation and observations

Boiling

• Boiling occurs throughout the liquid at a specific temperature, when vapour pressure equals external pressure.

Evaporation

• Evaporation occurs only at the surface, at temperatures below the boiling point.

Melting

• Melting the solid loses its shape while the volume stays constant.

Condensation

• Condensation droplets form on cooler surfaces.

Sublimation

• Sublimation a solid disappears directly into vapour.

Section 20 of 27Energy in state changes

1Endothermic

• Endothermic melting, vaporisation and sublimation need energy to overcome intermolecular forces.

2Exothermic

• Exothermic freezing, condensation and deposition release energy as particles come closer.

3Latent heat

• Latent heat the energy supplied during a state change is used to overcome intermolecular forces.

4Vaporisation versus melting

• Vaporisation versus melting vaporisation needs far more energy because particles must be completely separated.

5Strong forces

• Strong forces substances with strong intermolecular forces, such as water with hydrogen bonds, have higher melting and boiling points.

6Evaporation cooling

• Evaporation cooling surface particles with enough energy escape, which lowers the temperature of the remaining liquid.

Section 21 of 27State symbols

Symbols

• (s) solid, (l) liquid, (g) gas and (aq) aqueous, meaning dissolved in water.

Marks

• Marks state symbols are often marked in ionisation energy, lattice enthalpy (HL) and enthalpy of formation (HL).

Section 22 of 27Temperature and average kinetic energy

Temperature

• Temperature a measure of the average kinetic energy of the particles.

Proportional

• Proportional temperature in kelvin is directly proportional to average kinetic energy.

Speed

• Speed the higher the temperature, the faster the particles move on average.

Same temperature

• Same temperature all gases have the same average kinetic energy, but lighter gases move faster.

Depends on

• Depends on average kinetic energy depends on temperature in kelvin, not on mass or the identity of the substance.

Section 23 of 27Kelvin and Celsius

Kelvin scale

Kelvin scale the absolute temperature scale, with step size equal to 1 °C.

Absolute zero

• 0 K, where particles have no kinetic energy.

To kelvin

• T / K = θ / °C + 273.15.

To Celsius

• θ / °C = T / K − 273.15.

Room temperature

• Room temperature taken as 300 K in many ideal gas problems.

Section 24 of 27Interpreting a heating curve

Plot

• Plot temperature against energy supplied.

Heating a solid

• Heating a solid particles vibrate more, so temperature rises.

Melting

• Melting temperature stays constant while the solid becomes liquid.

Heating the liquid

• Heating the liquid particles move more freely, so temperature rises again.

Boiling

• Boiling energy overcomes intermolecular forces and the temperature is constant.

Heating the gas

• Heating the gas particles move rapidly with the highest average kinetic energy, so temperature rises.

Plateau

• Plateau temperature stays constant during melting and boiling even though energy is added.

Section 25 of 27More from the specification

1Chemical Separation by Filtration and Crystallisation

• Filtration separates insoluble solids from a liquid mixture based on particle size,
• while crystallisation separates dissolved solids from a solution by evaporating the solvent until crystals form upon cooling due to reduced solubility.

2Distillation and Separation by Boiling Points

• Simple distillation separates a liquid solvent from a solution or homogeneous mixture based on differences in boiling points, condensing the evaporated vapor back into pure liquid.

3Fractional Distillation of Complex Mixtures

• Fractional distillation utilizes a fractionating column to separate a mixture of miscible liquids with close boiling points into individual components through repeated vaporisation and condensation cycles.

4Differences Between Mixtures and Pure Elements/Compounds

• Mixtures consist of two or more pure substances physically combined without chemical bonding, retaining their individual physical properties and allowing separation by physical methods.
  • (elements or compounds)

5Fractional distillation

• Separating a mixture of liquids by their boiling points.

6Simple distillation

• Separating a solvent from a solution by evaporating and condensing it.

7Mixture

• Two or more substances mixed but not chemically combined.

8Filtration

• Separating an insoluble solid from a liquid using filter paper.

9Solubility

• Mass of solute that dissolves in a given mass of solvent.

10Distillation

• Separating a liquid from a solution by boiling and condensing the vapour.

11Property

• A feature that describes what a substance is like and what it does.

12Element

• A substance made of only one type of atom.

13Compound

• Two or more elements chemically combined in a fixed ratio.

14Chromatography

• Method separating substances by their different solubilities in a solvent.

Section 26 of 27Key terms

Term	Meaning
Element	A substance made of one kind of atom.
Compound	Two or more elements chemically bonded in a fixed ratio.
Mixture	Substances physically mixed in no fixed ratio.
Homogeneous mixture	A mixture with uniform composition throughout.
Heterogeneous mixture	A mixture with non-uniform composition.
Filtrate	The liquid that passes through the filter paper.
Residue	The solid left on the filter paper.
Absolute zero	0 K, the temperature of zero kinetic energy.

Term	Meaning
Simple distillation	Separates a solvent from a solute using a difference in boiling point.
Fractional distillation	Separates miscible liquids with similar boiling points using a column.
Chromatography	Separation by different solubility in a solvent and adsorption to a stationary phase.
Chromatogram	The pattern of separated spots on the paper.
Capillary action	The rise of liquid through a narrow space such as paper.
Kinetic molecular theory	The model describing states of matter by particle energy, arrangement and motion.

Term	Meaning
Sublimation	The change from solid directly to gas.
Deposition	The change from gas directly to solid.
Boiling	Vaporisation throughout the liquid when vapour pressure equals external pressure.
Evaporation	Vaporisation at the surface below the boiling point.
Kelvin	The SI unit of temperature, 0 K being absolute zero.
Latent heat	Energy absorbed or released during a state change without a temperature change.
Average kinetic energy	A measure of temperature, proportional to T in kelvin.

Section 27 of 27Exam technique

1

Saying a mixture has a fixed composition — it has no fixed ratio and no fixed melting or boiling point.

2

Saying temperature rises during melting or boiling — it stays constant while the energy overcomes intermolecular forces.

3

Using °C in gas and kinetic energy relationships — average kinetic energy depends on temperature in kelvin.

4

Saying heavier gases have more kinetic energy at the same temperature — only the speed is lower, the average kinetic energy is the same.

1

Using simple distillation for liquids with similar boiling points — fractional distillation is needed.

2

Drawing the chromatography start line in ink, which dissolves in the solvent — use pencil.

3

Placing the spots below the solvent level in chromatography.

4

Saying liquids have no fixed volume — only their shape is not fixed.

1

Saying temperature rises during melting or boiling — it stays constant on the plateau.

2

Calling melting exothermic — melting, vaporisation and sublimation are endothermic.

3

Using °C in relationships with kinetic energy — use kelvin.

4

Saying heavier gas particles have more kinetic energy at the same temperature — they move slower with the same average kinetic energy.