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

Section 1 of 27Elements, compounds and mixtures

Feature	Element	Compound	Mixture
Composition	One kind of atom	Two or more elements chemically bonded in a fixed ratio	Substances in no fixed ratio
Separation	Cannot be broken down chemically	Only by chemical reactions	By physical methods
Properties	Characteristic of the element	Different from the constituent elements	Components keep their own properties
Examples	Cu, O2, S8	H2O, NaCl	Air, brine, alloys

Elements, compounds and mixtures

Compound properties

• Compound properties sodium chloride differs from reactive sodium and toxic chlorine.

Mixture components

• Mixture components are interspersed but not chemically combined, e.g. nitrogen and oxygen in air.

Homogeneous mixture

• Homogeneous mixture has uniform composition and properties with one phase, e.g. air, solutions and bronze.

Heterogeneous mixture

• Heterogeneous mixture has non-uniform composition,
  • and separate components or phases can often be seen, e.g. concrete, orange juice with pulp and sand in water.

Section 2 of 27Choosing a separation method

• Principle
  • every method exploits a difference in a physical property such as boiling point, solubility, magnetism or density.

Technique	Separates	Property exploited
Solvation (dissolving)	Soluble from insoluble solid, e.g. salt from sand	Solubility in a chosen solvent
Filtration	Insoluble solid from liquid	Particle size
Crystallisation	Dissolved solid from solution	Solubility falls on cooling or evaporation
Recrystallisation	Impure solid purified	Solubility in hot and cold solvent
Simple distillation	Solvent from solution	Large boiling point difference
Fractional distillation	Miscible liquids	Small boiling point differences
Paper chromatography	Components of a solution	Solubility in mobile phase and attraction to paper
Magnetic separation	Iron from sulfur	Magnetism

Section 3 of 27Solvation, filtration and crystallisation

1Solvation

• Solvation solvent particles surround and attract solute particles, so only the desired component dissolves.
  • (hydration in water)

2Filtration

• Filtration the filtrate passes through the filter paper and the insoluble residue stays behind.

3Fine solids

• Fine solids vacuum (Büchner) filtration under reduced pressure is faster than gravity filtration.
• Very small or dense particles — centrifugation collects them at the bottom of the tube.

4Crystallisation steps

• Crystallisation steps heat gently to evaporate some solvent, test saturation with a cold glass rod, cool slowly, filter, wash with distilled water and dry on filter paper.

5Do not boil to dryness

• Do not boil to dryness crystals fail to form and hydrated salts such as CuSO₄·5H₂O lose water of crystallisation.
• Slow cooling — gives larger, purer crystals.

Section 4 of 27Recrystallisation

• Purpose
  • purifies an impure solid using differences in solubility in hot and cold solvent.

1

Dissolve the solid in the minimum volume of hot solvent.

2

Hot-filter to remove any insoluble impurities.

3

Cool slowly so the product crystallises while soluble impurities stay in solution.

4

Collect the crystals by Büchner filtration under reduced pressure.

5

Wash with a little fresh cold solvent.

6

Dry on filter paper.

Section 5 of 27Distillation

1Simple distillation

• Simple distillation separates a solvent from a solute, or a liquid with a much lower boiling point, by evaporation then condensation.

2Steps

• Steps heat the solution, the lowest boiling liquid evaporates, vapour condenses in the condenser and the distillate is collected.
• Example — water from salt solution.

3Fractional distillation

• Fractional distillation separates miscible liquids with similar boiling points using a fractionating column.

4Example

• Example ethanol (78 °C) and water (100 °C), heating to 78 °C to collect the ethanol first.
• Safety — an electric heater is used with flammable liquids.
• Industrial use — crude oil is separated by fractional distillation.

Section 6 of 27Paper chromatography

1

Draw a pencil baseline near the bottom of the paper, because pencil does not dissolve.

2

Place small spots of 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 (mobile phase) rise through the paper (stationary phase) by capillary action.

5

Dry the paper and observe the chromatogram.

Distance travelled

• Distance travelled components more soluble in the solvent travel further.

Adsorption

• Adsorption components more strongly attracted to the paper move more slowly.

Section 7 of 27States of matter

• Kinetic molecular theory
  • explains the states in terms of the energy, arrangement and motion of particles.

Property	Solid	Liquid	Gas
Shape and volume	Fixed shape and volume	Fixed volume, shape of container	Fills any container
Arrangement	Closely packed, regular, ordered	Close but randomly arranged	Widely spaced, random
Motion	Vibrate in fixed positions	Slide past each other	Fast and random
Density	High	Medium	Very low; easily compressed
Particle energy	Lowest	Medium	Highest

• Gas pressure
  • arises from particles colliding with the container walls.

Section 8 of 27Changes of state

• Nature
  • physical changes that are reversible and do not alter the chemical identity.

Change	Change of state	Energy
Melting	Solid to liquid	Endothermic
Vaporisation	Liquid to gas	Endothermic
Sublimation	Solid to gas	Endothermic
Freezing	Liquid to solid	Exothermic
Condensation	Gas to liquid	Exothermic
Deposition	Gas to solid	Exothermic

Energy direction

• Energy direction energy is absorbed to overcome interparticle attractions and released when particles come closer.

Boiling

• Boiling occurs throughout the liquid at the boiling point, when vapour pressure equals external pressure.

Evaporation

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

Pressure effect

• Pressure effect lowering external pressure, e.g. at altitude, lowers the boiling point.

Sublimation examples

• Sublimation examples iodine, dry ice (CO₂) and naphthalene sublime at atmospheric pressure.

State symbols

• (s), (l), (g) and (aq) for aqueous solution.

Section 9 of 27Temperature and average kinetic energy

Temperature

• Temperature a measure of the average kinetic energy of particles, and the Kelvin is the SI unit.

Conversion

• T/K = t/°C + 273.15, and a change of 1 K equals a change of 1 °C.

Absolute zero

• 0 K (−273.15 °C), where particles have minimum kinetic energy.

Proportionality

• Proportionality average kinetic energy is directly proportional to absolute temperature.

Same temperature

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

Distribution

• Distribution at any temperature particles have a range of speeds.

Section 10 of 27Heating curve

Region	Process	Temperature
Solid heating	Particles vibrate more as kinetic energy rises	Increases
Melting	Energy overcomes attractions and raises potential energy	Constant
Liquid heating	Particles move more freely	Increases
Boiling	Energy separates particles completely	Constant
Gas heating	Particles move rapidly with the highest kinetic energy	Increases

Plateaus

• Plateaus energy increases potential energy, not kinetic energy.
  • (particle spacing)

Boiling plateau

• Boiling plateau is longer than the melting plateau because far more energy is needed to separate particles completely.

Cooling

• Cooling the reverse occurs, with condensation and freezing releasing energy.

Section 11 of 27More from the specification

1Phase change energetics

• Melting and boiling are endothermic transitions where thermal energy is absorbed to overcome intermolecular forces between particles.

2Latent heat and plateau temperature

• During phase transitions, supplied heat increases potential energy rather than kinetic energy, so the temperature remains constant.

3Separation using a suitable solvent

• Differential solubility enables separating mixtures by dissolving soluble components in a suitable solvent while insoluble residues are filtered.

4Exothermic phase changes

• Freezing and condensation release latent heat into the surroundings as intermolecular attractive forces pull particles closer.

5Intermolecular forces

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

Section 12 of 27Simple and fractional distillation

Simple distillation

• Simple distillation separates a solvent from a dissolved solute, or a liquid with a much lower boiling point, using the difference in boiling point.

Fractional distillation

• Fractional distillation separates two or more miscible liquids with similar but different boiling points, such as ethanol and water.

Choice

• Choice simple distillation is not effective for liquids with similar boiling points, so fractional distillation is used.

Section 13 of 27Fractional distillation procedure

1

Heat the mixture in a round-bottomed flask; for ethanol (78 °C) and water (100 °C) heat to about 78 °C.

2

Vapour rises up the fractionating column, where repeated condensation and evaporation enrich it in the more volatile component.

3

The vapour passes into a condenser and is collected as liquid.

4

Change the receiving flask when the temperature rises to the next boiling point.

Fractional distillation procedure

Column

• Column is packed with glass beads, which give a large surface area for repeated evaporation and condensation.

Heating

• Heating heat gently and steadily, and use an electric heater rather than a naked flame with flammable liquids.

Temperature

• Temperature stays constant while one pure fraction distils.

Thermometer

• Thermometer the bulb sits at the side arm so it measures the boiling point of the vapour leaving.

Particle explanation

• Particle explanation the more volatile liquid has weaker intermolecular forces,
  • so more of its particles can escape from the surface at a given temperature.

Section 14 of 27Paper chromatography

• Principle
  • components move at different rates through a stationary phase carried by a mobile solvent.

1

Draw a pencil baseline and place a spot of the mixture on it; pencil is used because it does not dissolve (ink would run).

2

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

3

Allow the solvent to rise through the paper.

4

Remove the paper and mark the solvent front.

5

Read the chromatogram, which shows one spot per component.

• Distance travelled
  • substances more soluble in the solvent travel further.

Section 15 of 27Choosing a separation technique

Technique	Separates	Property used
Simple distillation	Solvent from a solute	Difference in boiling point
Fractional distillation	Miscible liquids, e.g. ethanol and water	Similar but different boiling points
Chromatography	Components of a mixture such as inks	Different solubility in the mobile phase

Section 16 of 27Kinetic molecular theory and states of matter

Kinetic molecular theory

• Kinetic molecular theory explains the physical properties of the states by the motion, spacing and energy of particles.

Solid

• Solid particles are close in a fixed regular arrangement and only vibrate about fixed positions.

Liquid

• Liquid particles are close but randomly arranged and slide past one another, so liquids flow.

Gas

• Gas particles are far apart, move rapidly and randomly, and have the highest kinetic energy.

Energy order

• Energy order particle energy increases from solid to liquid to gas.

Diagrams

• Diagrams state change diagrams emphasise particle spacing, order and energy flow.

Section 17 of 27State symbols and temperature

State symbols

• (s) solid, (l) liquid, (g) gas and (aq) aqueous, which are important in thermodynamic equations.

Temperature

• Temperature a measure of the average kinetic energy (E_k) of the particles, not of the total energy.

Unit

• Unit the kelvin (K) is the SI unit of temperature.

Section 18 of 27More from the specification

1

Separation of Insoluble Mixtures by Filtration

• Filtration separates an insoluble solid from a liquid suspension;
  • the mixture is poured through filter paper where the solid residue is retained while the clear filtrate passes through.

2

Crystallization from a Suitable Solvent

• Pure solid compounds are purified by dissolving the sample in a hot suitable solvent to form a saturated solution,
• which is then allowed to cool slowly so pure crystals precipitate.

3

Distinction Between Elements and Compounds

• Pure elements are fundamental substances composed of one atom type,
• whereas compounds consist of two or more different elements chemically bonded in fixed stoichiometric ratios.

4

Phase Changes and Absolute Temperature

• During substance melting or boiling, temperature remains constant as latent heat alters potential energy;
  • on the Kelvin scale, particle average kinetic energy is directly proportional to absolute temperature.

5

Filtration

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

6

Element

• A substance made of only one type of atom.

7

Compound

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

Section 19 of 27Energy during a change of state

Constant temperature

• Constant temperature the temperature stays constant while a substance changes state.

Use of energy

• Use of energy supplied energy overcomes intermolecular forces, raising potential energy rather than kinetic energy.

Within one state

• Within one state particles move more freely and gain kinetic energy, so the temperature rises.

Direction

• Direction melting, vaporisation and sublimation are endothermic, and freezing, condensation and deposition are exothermic.

Section 20 of 27Observations during changes of state

Change	Observation
Melting	Solid becomes liquid; shape is lost but volume stays constant
Freezing	Liquid becomes rigid and regains its shape
Boiling	Bubbles form throughout the liquid as vapour escapes
Condensation	Gas forms droplets on cooler surfaces
Sublimation	Solid disappears directly into vapour

Section 21 of 27Reading a heating curve

Sloping sections

• Sloping sections heating within one state.

Flat sections

• Flat sections a change of state.

1

The solid warms: particles vibrate more strongly and kinetic energy rises.

2

At the melting point the line is flat: energy overcomes the forces holding the lattice.

3

The liquid warms: particles move more freely and gain kinetic energy.

4

At the boiling point the line is flat: energy separates the particles completely.

5

The gas warms: kinetic energy continues to rise.

• Length of plateaus
  • the boiling plateau is longer because much more energy is needed to separate particles completely than to loosen them.

Section 22 of 27Evaporation, boiling and sublimation

Evaporation

• Evaporation occurs only at the surface, at any temperature above freezing, when some particles have enough energy to escape.

Boiling

• Boiling occurs throughout the liquid at one fixed temperature, when vapour pressure equals external pressure.

Sublimation

• Sublimation the direct change from solid to gas, as in iodine and solid carbon dioxide.

Deposition

• Deposition the reverse change, from gas directly to solid.

Section 23 of 27The Kelvin scale

Proportionality

• Proportionality temperature in kelvin is directly proportional to the average kinetic energy of the particles.

Absolute zero

• 0 K, the temperature of minimum kinetic energy.

Conversion

• θ/°C = T/K − 273.15, and K = °C + 273 is used for less precise work.

Interval

• Interval a difference of 1 K is identical to a difference of 1 °C.

Room temperature

• Room temperature taken as 300 K in many ideal gas problems, which is about 27 °C.

Notation

• Notation written as K, not °K.

Section 24 of 27Applications of particle energy ideas

Applications of particle energy ideas

Steam burns

• Steam burns steam causes worse burns than boiling water at the same temperature because extra energy is released on condensation.

Puddles

• Puddles evaporate on a warm day below the boiling point because some surface particles have enough energy to escape.

Heating curve interpretation

• Heating curve interpretation each section can be assigned to a state or a change of state.

Section 25 of 27More from the specification

More from the specification

Separation by filtration and solubility

• Separation by filtration and solubility mixtures of insoluble solids and soluble components separate by adding a solvent followed by filtration.

Crystallisation from saturated solution

• Crystallisation from saturated solution evaporating warm solvent decreases solute solubility, causing pure solute crystals to form upon cooling.

Simple distillation for volatile components

• Simple distillation for volatile components simple distillation separates a liquid solvent from dissolved solutes using differences in volatile boiling point properties.

Chromatography

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

Fractional distillation

• Separating a mixture of liquids by their boiling points.

Simple distillation

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

Solvent

• Substance that a solute dissolves in.

Mixture

• Two or more substances mixed but not chemically combined.

Filtration

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

Solubility

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

Distillation

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

Property

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

Element

• A substance made of only one type of atom.

Compound

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

Section 26 of 27Key terms

Term	Meaning
Element	A pure substance made of only one type of atom.
Compound	A pure substance of two or more elements chemically combined in a fixed ratio.
Mixture	Two or more substances physically combined in no fixed ratio.
Homogeneous mixture	A mixture with uniform composition and one phase.
Heterogeneous mixture	A mixture with non-uniform composition and distinguishable phases.
Sublimation	The change of state from solid directly to gas.
Absolute zero	0 K, the temperature of minimum particle kinetic energy.

Term	Meaning
Fractional distillation	Separation of miscible liquids with different boiling points using a fractionating column.
Chromatogram	The pattern of spots left on the paper after chromatography.
Kinetic molecular theory	A model describing matter as particles in constant motion.
Temperature	A measure of the average kinetic energy of the particles.
Kelvin	The SI unit of temperature.
State symbol	The label (s), (l), (g) or (aq) after a formula.

Term	Meaning
Melting	The change from solid to liquid.
Boiling	Vaporisation throughout the liquid at its boiling point.
Condensation	The change from gas to liquid.
Freezing	The change from liquid to solid.
Absolute zero	0 K, the temperature at which particles have minimum kinetic energy.
Heating curve	A graph of temperature against time as a substance is heated.

Section 27 of 27Exam technique

1

Saying temperature rises during melting — it stays constant while energy changes potential energy.

2

Treating a mixture as having a fixed formula — its components are in any proportion and keep their properties.

3

Writing the neutral scale as °C in gas calculations — absolute temperature in kelvin is needed.

4

Evaporating a crystallisation solution to dryness — slow cooling of a saturated solution gives crystals.

1

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

2

Drawing the chromatography baseline in ink or letting the spots sit below the solvent level.

3

Saying temperature measures total energy — it measures average kinetic energy.

4

Omitting or misusing state symbols in equations.

1

Saying heat supplied during melting raises the temperature — it is used to overcome intermolecular forces.

2

Subtracting 273.15 when converting Celsius to kelvin — add it instead.

3

Writing °K — the unit is K without a degree sign.

4

Confusing boiling with evaporation — boiling occurs throughout the liquid at the boiling point.