Particles and separation

Question 1

The Three States of Matter

Answer 1

States: Solid, Liquid, Gas
Changes of State:
Melting (Solid → Liquid)
Freezing (Liquid → Solid)
Boiling/Evaporation (Liquid → Gas)
Condensation (Gas → Liquid)
Sublimation (Solid → Gas)

Question 2

Particle Arrangement and Movement

Answer 2

Solids: Tightly packed, vibrate in place.
Liquids: Loosely packed, move around each other.
Gases: Very far apart, move freely and randomly.

Question 3

Predicting States of a Substance

Answer 3

Solid: Fixed shape and volume.
Liquid: Takes the shape of the container but has fixed volume.
Gas: Fills the entire container, no fixed shape or volume.

Question 4

Energy of Particles in States of Matter

Answer 4

Solid: Low energy.
Liquid: Medium energy.
Gas: High energy.

Question 5

Changes During State Changes

Answer 5

Movement and Arrangement:
Particles gain energy to break bonds (melting/boiling).
Particles lose energy and form bonds (freezing/condensation).

Question 6

Energy Change During State Changes

Answer 6

Energy Change:
Energy is absorbed to break intermolecular forces (melting/boiling).
Energy is released when forming bonds (freezing/condensation).

Question 7

Pure Substance vs Mixture

Answer 7

Pure Substance: Single element/compound, sharp melting point.
Mixture: Two or more substances, melting point varies.

Question 8

Melting Point and Purity

Answer 8

Pure Substances: Have a sharp melting point.
Mixtures: Melt over a range of temperatures.

Question 8

Particle Behavior at Melting Point

Answer 8

Pure Substance Melting: Particles gain enough energy to break bonds and move from a solid to a liquid state.

Question 9

Heating Curve and Melting Point

Answer 9

Flat Line on Heating Curve: Indicates a phase change; temperature stays constant while the substance melts.

Question 10

Filtration and Crystallisation

Answer 10

Filtration: Separates insoluble solids from liquids (e.g., sand and water).
Crystallisation: Separates a solute from a solution by evaporating the solvent (e.g., salt from seawater).

Question 11

Formation of Crystals During Crystallisation

Answer 11

Crystallisation: As the solvent evaporates, the solute forms crystals due to reduced solubility at lower temperatures.

Question 12

Filtration Process

Answer 12

Process: Pour mixture through filter paper; solid residue stays behind, liquid passes through.
Risk Reduction: Use of gloves, goggles, and careful heating during crystallisation.

Question 13

Separating Mixtures by Chromatography

Answer 13

Chromatography: Separates substances based on their solubility and affinity for the stationary phase.
Mixtures: Produce multiple spots on a chromatogram.

Question 14

Chromatography Diagrams

Answer 14

Set-up: Spot the sample on a pencil line of chromatography paper, place in solvent. The solvent moves up the paper, separating substances.

Question 15

Identifying Pure Substances in Chromatograms

Answer 15

Pure Substance: One spot.
Mixture: Multiple spots.

Question 16

Rf Value Calculation

Answer 16

Rf Value:
Rf =

Distancemovedbysubstance/Distancemovedbysolvent

​
Use: Identify substances by comparing Rf values to known values.

Question 17

Simple vs Fractional Distillation

Answer 17

Simple Distillation: Used to separate liquids with significantly different boiling points (e.g., water from ink).
Fractional Distillation: Used for separating liquids with closer boiling points (e.g., crude oil).

Question 18

Fractional Distillation Process

Answer 18

Process:
Heat the mixture.
Vapors rise through a fractionating column.
Substances condense at different heights based on boiling points.

Question 19

Risk in Distillation

Answer 19

Precautions:
Use heat sources carefully.
Ensure good ventilation.
Avoid pressure build-up by not sealing apparatus.

Question 20

Water for Chemical Analysis

Answer 20

Why No Dissolved Salts?: Salts may interfere with reactions or give false results.

Question 21

Fresh Water from Seawater

Answer 21

Method: Desalination by distillation. Heat seawater, condense steam to collect fresh water.

Question 22

Making Water Safe for Drinking

Answer 22

Steps:
Filtration: Remove large particles.
Sterilisation: Kill bacteria using chlorine or UV light.

Question 23

Evaluating Water Purification Risks

Answer 23

Risk: Contamination, harmful chemicals in water.
Control: Use appropriate purification techniques like filtration, distillation, and sterilisation.