Introduction To The Particulate Nature Of Matter

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Elements and Compounds

Elements are substances made from one kind of atom and cannot be chemically broken down into simpler substances.
Elements take part in chemical reactions in which new substances are made, often involving an energy change.
In chemical reactions, atoms combine in fixed ratios to give full outer shells of electrons, producing compounds.
Compounds are made from two or more elements chemically bonded together.
The properties of a compound can be quite different from the properties of the elements that form it (e.g., sodium chloride vs sodium and chlorine).

Ball-and-stick models of common elements and compounds

Mixtures

Mixtures contain more than one element or compound in no fixed ratio.
The components of a mixture are interspersed but not chemically combined.
The components of a mixture retain their own characteristic properties (e.g., oxygen in air still supports combustion).
A homogeneous mixture has uniform composition and properties throughout (e.g., air, bronze).
A heterogeneous mixture has non-uniform composition, so its properties are not the same throughout (e.g., concrete, orange juice with pulp).
It is often possible to see the separate components in a heterogeneous mixture, but not in a homogeneous mixture.

Particle diagram showing elements, compounds and mixtures

Separating Mixtures: Solubility and Filtration

Separation techniques take advantage of differences in physical properties such as boiling point, solubility, magnetism, or density.
Solvation is the process where solvent particles surround and attract solute particles; in water it is called hydration.
Filtration separates an undissolved (insoluble) solid from a liquid or solution using filter paper.
In filtration, the liquid that passes through is the filtrate and the solid left behind is the residue.
Filtration works because solid particles are too large to pass through the pores in the filter paper.
Vacuum filtration can be used for very fine solids that clog filter paper under gravity filtration; centrifugation can also separate solid–liquid mixtures.

Filtration apparatus

Separating Mixtures: Crystallisation and Recrystallisation

Crystallisation separates a dissolved solid from a solution when the solid is more soluble in hot solvent than cold.
To crystallise, heat the solution gently to evaporate some solvent, then allow it to cool slowly until crystals form.
Do not boil to dryness, as this may prevent crystal formation; cool slowly to allow larger crystals to grow.
Recrystallisation purifies an impure solid by dissolving it in a minimum amount of hot solvent and allowing it to crystallise as the solution cools.
Impurities remain in the solvent when cooled, while the purified product crystallises.
Büchner filtration under reduced pressure is faster and more effective than gravity filtration for collecting crystals.

Crystallisation by evaporation and cooling

Separating Mixtures: Distillation and Chromatography

Simple distillation separates a solvent from a solute or a pure liquid from a mixture, based on differences in boiling point.
In simple distillation, the liquid with the lowest boiling point evaporates first, then its vapour is condensed and collected as the distillate.
Fractional distillation separates two or more miscible liquids with similar boiling points using a fractionating column (e.g., ethanol and water, crude oil).
Paper chromatography separates dissolved substances based on differences in solubility and adsorption to the paper.
In chromatography, substances more soluble in the solvent travel further; those more strongly adsorbed to the paper move more slowly.
The pattern of separated spots is called a chromatogram.
Magnetic separation uses differences in magnetic properties (e.g., removing iron filings from sulfur).

Paper chromatography

The Three States of Matter

Solids have a fixed shape and volume; particles are closely packed in a regular, ordered pattern and can only vibrate in place.
Liquids have a fixed volume but take the shape of their container; particles are close together but randomly arranged and can slide past one another.
Gases have no fixed shape or volume; particles are widely spaced, randomly arranged, and move quickly in all directions.
Particle motion in gases causes collisions, which generate pressure.
Density decreases from solid to liquid to gas due to increasing particle separation.
Particle energy increases from solid to liquid to gas.

Particle arrangements in solids, liquids and gases

Changes of State

State changes are physical changes and are reversible; they involve energy transfer but do not alter the chemical identity of the substance.
Melting: solid → liquid; Freezing: liquid → solid.
Vaporisation: liquid → gas, including boiling (throughout the liquid at a specific temperature) and evaporation (only at the surface, below boiling point).
Condensation: gas → liquid; Sublimation: solid → gas; Deposition: gas → solid.
Energy is always required to overcome intermolecular forces, so melting, vaporisation, and sublimation are endothermic.
Energy is released when particles come closer, so freezing, condensation, and deposition are exothermic.
State symbols in equations: (s) solid, (l) liquid, (g) gas, (aq) aqueous.

Changes of state

Average Kinetic Energy and Temperature

Temperature is a measure of the average kinetic energy (Ek) of the particles in a substance.
The Kelvin (K) is the SI unit of temperature; temperature in Kelvin is directly proportional to average kinetic energy.
The higher the temperature, the faster the particles move on average.
At the same temperature, all gases have the same average kinetic energy, but lighter gases move faster and heavier gases move slower.
Convert Celsius to Kelvin: T(K) = T(°C) + 273.15; Kelvin to Celsius: T(°C) = T(K) − 273.15.
0 K (absolute zero) is the temperature at which particles have no kinetic energy.

Interpreting Heating Curves

During heating of a solid, particles vibrate more as they gain kinetic energy, so temperature increases.
During melting (solid → liquid), energy is used to overcome intermolecular forces, not to increase kinetic energy, so temperature remains constant.
During heating of a liquid, particles move more freely and gain kinetic energy, so temperature rises again.
During boiling (liquid → gas), energy goes into overcoming intermolecular forces, so temperature remains constant.
After boiling, the substance is a gas; particles move rapidly and have the highest average kinetic energy, so temperature increases again.
Observations: melting loses shape but volume remains constant; boiling forms bubbles throughout; condensation forms droplets on cooler surfaces; freezing regains rigid shape; sublimation solid disappears directly into vapour.

A heating curve

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Übungsfragen

Gratis-Vorschau — 8 von 61 Fragen. Registriere dich, um alle zu sehen.

1.Which equation represents deposition?
Medium
- AI₂(g) → I₂(s)
- BI₂(s) → I₂(g)
- CH₂O(g) → H₂O(l)
- DCO₂(s) → CO₂(g)
2.Which statements about mixtures are correct? (select all that apply)
Medium
- AMixtures can contain elements and compounds.
- BThe components of a mixture must be in the same state.
- CThe components of a mixture keep their own properties.
- DMixtures have a fixed ratio of components.
3.Which of the following is a heterogeneous mixture?
Medium
- AAn aqueous solution of copper(II) chloride
- BAn alloy of iron, carbon and chromium
- CA mixture of sulfur and potassium chloride
- DA mixture of ammonia, hydrogen sulfide and methane gases
4.The components of a mixture are chemically combined.
Easy
True or false?
5.Match each change of state with its correct description.
Medium
- Melting
- Freezing
- Sublimation
- Deposition
- solid to liquid
- liquid to solid
- solid to gas
- gas to solid
6.Which statement is correct about recrystallisation when purifying a solid?
Medium
- AThe solid must be insoluble in the hot solvent
- BThe impurities will remain in the solvent when cooled
- CThe yield of product is the same after recrystallisation
- DThe solvent is in excess during recrystallisation
7.Which of the following mixtures cannot be classified as homogeneous?
Medium
- ASalt solution
- BBrass
- COrange juice that has been filtered
- DConcrete
8.Which of the following are examples of homogeneous mixtures? (select all that apply)
Medium
- AAir
- BBronze
- CConcrete
- DOrange juice with pulp
- ESalt solution

Mehr Fragen

9.Which of the following state changes are exothermic? (select all that apply)
Medium
- AFreezing
- BMelting
- CCondensation
- DSublimation
- EDeposition
10.Which statements about the separation of a mixture of salt and sand are correct? (select all that apply)
Hard
- AAdding water dissolves the salt but not the sand
- BFiltration separates the sand as the residue
- CThe salt solution passes through the filter paper as the filtrate
- DEvaporation of the filtrate leaves the sand behind
- EThe salt and sand can be separated because they have different solubilities in water
11.Which of the following statements about distillation are correct? (select all that apply)
Hard
- ASimple distillation separates a solvent from a solution based on boiling point
- BFractional distillation is used to separate miscible liquids with similar boiling points
- CIn simple distillation, the liquid with the highest boiling point evaporates first
- DThe distillate is the purified liquid collected after condensation
- EFractional distillation uses a fractionating column to improve separation
12.Match each separation technique with the physical property it relies on.
Medium
- Filtration
- Crystallisation
- Chromatography
- Magnetic separation
- Solubility
- Solubility and adsorption
- Magnetic properties
- Particle size
13.Match each change of state with its correct name.
Medium
- Solid to liquid
- Liquid to gas
- Gas to solid
- Solid to gas
- Deposition
- Sublimation
- Melting
- Vaporisation
14.Arrange the steps of simple distillation in the correct order.
Medium
- Heat the solution in a round-bottomed flask
- The liquid with the lowest boiling point evaporates first
- Vapour passes into the condenser and condenses
- The distillate is collected in a clean beaker
15.Arrange the stages of recrystallisation in the correct order.
Medium
- Dissolve the impure solid in the minimum amount of hot solvent
- Perform hot filtration if solid impurities remain
- Allow the solution to cool slowly
- Collect the crystals by filtration
- Wash the crystals with cold solvent and dry
16.In a homogeneous mixture, the components are chemically combined.
Easy
True or false?
17.During boiling, the temperature of a pure liquid remains constant until all the liquid has vaporised.
Easy
True or false?
18.At the same temperature, lighter gas particles have a higher average speed than heavier gas particles.
Medium
True or false?
19.A sample of a gas is cooled at constant pressure from 400 K to 200 K. Which statement about the average kinetic energy of the gas particles is correct?
Medium
- AIt halves because temperature in kelvin halves.
- BIt stays the same because the gas is the same substance.
- CIt decreases by a factor of 4.
- DIt doubles because the gas is cooled.
20.A heating curve for a pure substance shows a horizontal plateau at 0 °C and another at 100 °C. What is happening to the energy supplied during the plateau at 100 °C?
Medium
- AIt is used to overcome intermolecular forces, so the temperature stays constant.
- BIt increases the kinetic energy of the particles, so the temperature stays constant.
- CIt is released as the particles move closer together.
- DIt breaks chemical bonds within the molecules.
21.At the same temperature, which gas has particles with the highest average speed?
Easy
- AHelium, He
- BNitrogen, N2
- COxygen, O2
- DCarbon dioxide, CO2
22.A student heats a sample of a pure solid and records the temperature every minute. The graph shows a plateau at 80 °C, followed by a rise, then a second plateau at 120 °C. Which statements are correct? (select all that apply)
Medium
- AThe first plateau corresponds to melting.
- BThe second plateau corresponds to boiling.
- CThe melting point of the substance is 120 °C.
- DDuring the plateaus, the average kinetic energy of the particles increases.
- EThe substance is a liquid between the two plateaus.
23.At the same temperature, all gases have the same average kinetic energy.
Easy
True or false?
24.A student separates a mixture of ethanol (boiling point 78 °C) and water (boiling point 100 °C) using fractional distillation. Which statement explains why ethanol is collected first?
Medium
- AEthanol has weaker intermolecular forces and a lower boiling point, so it evaporates first.
- BEthanol has stronger intermolecular forces and a higher boiling point, so it evaporates first.
- CWater has weaker intermolecular forces and a lower boiling point, so it evaporates first.
- DBoth liquids evaporate at the same rate because they are miscible.
25.A student purifies an impure solid by recrystallisation. Which statement correctly describes the role of the solvent?
Medium
- AThe solid should be highly soluble in hot solvent and poorly soluble in cold solvent.
- BThe solid should be insoluble in hot solvent and soluble in cold solvent.
- CThe solvent should dissolve both the solid and the impurities equally at all temperatures.
- DThe solvent should be added in large excess to maximise yield.
26.A mixture of salt and sand is separated by adding water, filtering, and then evaporating the filtrate. Which physical property difference is used in the filtration step?
Medium
- ASolubility in water
- BBoiling point
- CMagnetism
- DDensity
27.A sample of pure sulfur dioxide is heated from −100 °C to 0 °C. The heating curve shows a plateau at −75 °C and another at −10 °C. Which statements are correct? (select all that apply)
Hard
- AThe first plateau corresponds to melting.
- BThe second plateau corresponds to boiling.
- CBetween the two plateaus, the substance is a liquid.
- DThe melting point of sulfur dioxide is −10 °C.
- EDuring the plateaus, the temperature remains constant because energy is used to overcome intermolecular forces.
28.A mixture of iodine and sand is placed in a beaker and heated gently. Iodine sublimes and is collected as a solid on a cold surface. Which physical property difference allows this separation?
Medium
- ADifference in ability to sublime
- BDifference in solubility in water
- CDifference in magnetic properties
- DDifference in density
29.Which of the following statements about the separation of a mixture of iodine and sand by sublimation are correct? (select all that apply)
Medium
- AIodine sublimes and is collected as a solid on a cold surface.
- BSand remains behind in the beaker.
- CThe process involves a chemical change.
- DIodine can be separated from sand because it dissolves in water.
- EThe separation relies on a difference in physical properties.
30.During simple distillation, the thermometer bulb should be placed in the liquid in the round-bottomed flask to measure the boiling point accurately.
Easy
True or false?
31.Match each separation technique with the physical property difference it relies on.
Medium
- Filtration
- Crystallisation
- Chromatography
- Magnetic separation
- Solubility difference in hot and cold solvent
- Difference in solubility and adsorption
- Difference in magnetic properties
- Difference in solubility (insoluble solid from liquid)
32.Arrange the steps of separating a mixture of sand and salt by filtration and evaporation in the correct order.
Medium
- Add water to the mixture and stir.
- Filter the mixture to separate sand from the salt solution.
- Evaporate the filtrate to obtain solid salt.
- Collect the sand as the residue.
33.A student purifies an impure solid by recrystallisation. The solid is soluble in hot solvent but much less soluble in cold solvent. Which statement explains why the crystals formed are purer than the original solid?
Hard
- AImpurities remain dissolved in the cold solvent.
- BImpurities are chemically bonded to the solid.
- CImpurities have higher melting points and crystallise first.
- DImpurities are removed by evaporation.
34.A student uses paper chromatography to analyse a mixture of dyes. The solvent front travels 10.0 cm from the baseline. A dye spot travels 6.0 cm from the baseline. What is the Rf value of this dye?
Hard
- A0.60
- B1.67
- C0.40
- D6.0
35.A student sets up apparatus to separate a mixture of propanone (boiling point 56 °C) and water (boiling point 100 °C) using simple distillation. Which statement explains why the separation is possible?
Challenge
- APropanone has weaker intermolecular forces than water, so it evaporates first.
- BWater has weaker intermolecular forces than propanone, so it evaporates first.
- CPropanone and water have the same boiling point, so they cannot be separated.
- DPropanone has stronger intermolecular forces than water, so it condenses first.
36.Which equation does not represent sublimation or deposition?
Easy
- ANH₃(g) + HCl(g) → NH₄Cl(s)
- BI₂(s) → I₂(g)
- CC₁₆H₁₀O(s) → C₁₆H₁₀O(g)
- DH₂O(g) → H₂O(s)
37.A compound is made from two or more elements chemically bonded together.
Easy
True or false?
38.The correct combination relating to state change, particles and energy is:
Medium
- ASubliming: particles move further apart; particles gain energy
- BVaporising: particles come closer together; particles gain energy
- CMelting: particles move further apart; particles lose energy
- DCondensing: particles come closer together; particles gain energy
39.Chlorofluorocarbons have been used extensively as liquid coolants in refrigerators and air conditioners. Which of the following descriptions explains how a refrigerant works?
Hard
- AAt high pressure the liquid evaporates and absorbs heat, cooling the surroundings
- BAt low pressure the liquid evaporates and absorbs heat, cooling the surroundings
- CAt high pressure the liquid condenses and absorbs heat, cooling the surroundings
- DAt low pressure the liquid condenses and absorbs heat, cooling the surroundings
40.Which of the following are physical changes? (select all that apply)
Medium
- AMelting of ice
- BSublimation of iodine
- CCombustion of methane
- DCondensation of steam
- ERusting of iron
41.What is the name of the process when a solid changes directly into a gas?
Easy
42.What is the name of the process when a gas changes into a liquid?
Easy
43.Complete the sentence about homogeneous mixtures.
Medium
A homogeneous mixture has ____ composition and properties throughout, for example ____.
44.Convert 300 K to degrees Celsius. Give your answer to 2 decimal places.
Medium
45.Convert 350 K to degrees Celsius. Give your answer to 2 decimal places.
Easy
46.A sample of gas is at 25 °C. What is this temperature in kelvin? Give your answer to 2 decimal places.
Medium
47.Complete the sentence about the kinetic molecular theory.
Easy
Temperature is a measure of the average ____ energy of the particles in a substance.
48.Complete the sentence about the Kelvin scale.
Medium
0 K is known as ____ zero, the temperature at which particles have no kinetic energy.
49.Name the three states of matter in order of increasing average kinetic energy of their particles.
Medium
The three states in order of increasing average kinetic energy are ____, ____, and ____.
50.What is the name of the process where a solute dissolves in a solvent because solvent particles surround and attract solute particles?
Medium
51.Name the separation technique used to purify an impure solid by dissolving it in hot solvent and allowing it to crystallise on cooling.
Medium
52.A gas is at 25 °C. What is this temperature in kelvin? Give your answer to 2 decimal places.
Medium
53.Explain why the temperature remains constant during melting, even though energy is being supplied.
Hard
54.Explain why gaseous iodine occupies a significantly greater volume than solid iodine.
Hard
55.Describe how an increase in temperature affects the movement of particles in a liquid.
Hard
56.Explain, in terms of solubility and adsorption, how paper chromatography separates the components of a mixture of dyes.
Challenge
57.A student separates a mixture of propanone (boiling point 56 °C) and water (boiling point 100 °C) using distillation. Describe, with reference to boiling points and intermolecular forces, how this separation is achieved.
Hard
58.Convert 300 K to degrees Celsius. Give your answer to 2 decimal places.
Medium
- A26.85 °C
- B32.23 °C
- C24.16 °C
- D29.54 °C
59.Convert 350 K to degrees Celsius. Give your answer to 2 decimal places.
Easy
- A69.17 °C
- B76.85 °C
- C84.53 °C
- D92.21 °C
60.A sample of gas is at 25 °C. What is this temperature in kelvin? Give your answer to 2 decimal places.
Medium
- A327.96 K
- B268.34 K
- C357.77 K
- D298.15 K
61.A gas is at 25 °C. What is this temperature in kelvin? Give your answer to 2 decimal places.
Medium
- A327.96 K
- B268.34 K
- C298.15 K
- D357.77 K

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