Methods of Separation

Mixtures can be separated into their constituents by physical methods. Separation techniques are physical techniques.

Factors affecting which separation techniques to use
- Solubility
- States
- Boiling and Melting Point

Separation methods:

• - Filtration
• - Separating funnel
• - Paper Chromatography
• - Evaporation to dryness
• - Simple distillation
• - Fractional distillation

Filtration: 

A mixture of two solids can be separated by filtration if one of them is soluble in a solvent but the other is not. For example, the mixture of salt and sand can be separated by filtration using water as the solvent.

Separating funnel: 

To separate two immiscible liquids, a separating funnel is used. For example, to separate oil and water the separating funnel is used.

To separate miscible liquids, they must be separated by fractional distillation. Fractional distillation can separate a solution of ethanol and water. A column, called the fractionating column is attached to the round-bottomed flask and the condenser. Many glass beads in the fractionating column provide a large surface area for vapour to condense on. Other than glass beads, a fractionating column may be filled with plate or a spiral. 

During fractional distillation, the liquid with the lowest boiling point will distil over to the condenser first, the vapours of liquids with higher boiling points condense along the fractionating column and re-enter the round bottomed flask. 

Chromatography :

- Separate different colour dyes

- The more soluble dyes move further up the chromatography paper than the less    soluble dyes.

Evaporation to dryness : 

- Solute required is left behind in the dish while the solvent escapes as water vapour

Kinetic Particle Theory

Scientific model

- What is a scientific model?

ü  A representation, a prototype or replica of the object/phenomenon that could well explains its physical properties.

ü  It can be represented using animation or static diagrams.

ü  Phenomenon includes physical phenomenon like diffusion, dissolving, boiling, condensation, evaporation, melting, sublimation etc.

ü  Physical properties include volume, density, conductivity etc…

- Types of Models

ü  Physical model

ü  Scale models

ü  Computer models

ü  Mathematical models

- Models are used to…

ü  Make predictions

ü  Help in investigations

ü  Summarize data

- Characteristics of Models

ü  Models have approximations to Nature

ü  Models have limitations eg, they do not represent nature in every aspect

ü  Scientists can use different models to describe the same thing (eg. Bohr’s model and Schroedinger’s equation)

ü  Models are subject to revision and/or rejection when there’s new information.

- What are assumptions & limitations?

ü  Assumptions are valid statements to set the parameters for the model to work. Without the assumptions, the principles of the model become invalid or irrelevant.

ü  Limitations are features of the model not aligned with the actual properties and go against the principles of the phenomenon.

- Assumptions of the Kinetic Particle Model

ü  Particles are in constant motion and in random directions.

ü  Particles possess kinetic energy.

ü  Forces of attraction exist between particles.

ü  Heavier particles travel slower than lighter particles.

ü  Particles do not stick to each other after collision (elastic collision).

ü  Particles do not stick with the walls of container and bounces back after collision with the walls of container.

ü  Particles travel in a straight line.

ü  Particles are small and discrete.

- Limitations of the Kinetic Particle Model

ü  Forces of attraction between particles are not seen in the model. (Only for static picture but can be shown clearly on animation)

ü  Movement of particles in terms of direction and speed may not be accurately captured on static picture but can be shown clearly on animation.

ü  Size of the particles of an element may not be uniform. (Size of particles can be drawn uniformly) NOT LIMITATION

ü  Distance between particles in model may not be scaled accurately to the actual distance between particles.

ü  Size of the particles in model may not be scaled accurately to the actual particles’ size. (You can scale the particle’ size accurately in both static picture & animation) NOT LIMITATION

Analogy to explain Kinetic Particle Theory

- One example : A rock concert to illustrate inter-conversion of solid (during concert) to liquid (when concert ends) - (melting)

Features similar to kinetic particle model	Assumptions	Limitations
ü  During concert, people are closely packed & jumping at fixed positions, just like particles in solid state etc... ü  When concert ends, people are moving disorderly sliding past each other but still closely packed, just like particles in liquid state etc.	ü  People are in large in numbers yet small in size relative to entire concert hall. ü  People do not stick to each other upon collision. ü  Each person possesses kinetic energy. ü  Each person moves in constant and random motion.	ü  People are of different sizes/masses unlike particles that are of same size/mass of same substance. ü  There is no force of attraction between people unlike particles that consist strong forces of attraction between them. ü  People are not standing in ordered arrangement, unlike particles in solid state in ordered arrangement.

Physical properties of 3 states

- A solid

ü  Cannot be compressed, thus a definite volume

ü  Has definite shape

ü  High density

ü  Force of attraction is the most

ü  Arrangement of particles are very packed and motion is very little

- A liquid

ü  Cannot be easily compressed, thus a definite volume

ü  Has no definite shape – take the shape of the container

ü  High density (usually lower than solid)

ü  Force of attraction is less than solids

ü  The arrangement of the particles are slightly packed and the motion is a little more than solids

- A gas

ü  Can be easily compressed, thus an indefinite volume

ü  Has no definite shape – take the shape of the container

ü  Low density

ü  Force of attraction is the least

ü  The arrangement of the particles are loosely-packed and the motion is in constant random movement.

Elements, Compounds and Mixture

Elements

- What is an element?

ü  An element is a substance made up of entirely from one type of atom.

- Every element is given a name and a chemical symbol

ü  First letter is always capitalised

ü  Any other letter that follows is in letter case

Element	Chemical Symbol
Hydrogen	H
Carbon	C
Calcium	Ca
Cobalt	Co
Iron	Fe
Gold	Au

- Naming Elements

ü  Name and chemical symbols are standardized internationally by IUPAC (International Union of Pure and Applied Chemistry)

ü  Some elements are named after countries and famous people

- Symbols of Elements

ü  From the name of elements or from the names of elements in Latin

- Periodic Table

ü  Horizontal row of elements are called Periods.

ü  Vertical columns of elements are called Groups.

- Classification of Elements

ü  There are 2 major groups of elements – metals and non-metals.

ü  Iron is a metal. Oxygen is a non-metal.

ü  Metals and non-metals are groped separately on the Periodic Table.

ü  There are some elements called metalloids which behave like both metals and non-metals.

ü  2 ways to classify elements

ü  First is by the number of sub atomic particles which determine their position in the Periodic Table

ü  Second is by their properties such as melting and boiling points etc.

ü  The number of sub atomic particles is related to their properties.

Differences between metals and non-metals

Metals	Non-metals
Shiny (lustrous)	Dull
Solid at room temperature (except Hg)	Usually gases or liquids at room temperature
Malleable, sonorous, ductile	Brittle (if solid)
Usually high melting and boiling points	Usually low melting and boiling points
Good conductors of heat	Usually poor conductors of heat
Good conductors of electricity	Usually poor conductors of electricity

Compounds

- What is a compound?

ü  A compound is a pure substance that contains two or more elements chemically combined.

Compound	Elements present
Common salt (sodium chloride)	Sodium, chlorine
Marble (calcium carbonate)	Calcium, carbon, oxygen
Copper (II) sulphate	Copper, sulphur, oxygen
Hydrogen chloride	Chlorine, hydrogen

- Naming Compounds

ü  A compound made up of 2 elements has a name that ends in –ide.

ü  A compound that contains hydroxide ions, OH- (a negatively charged ion made up of oxygen and hydrogen) is named a hydroxide.

ü  A compound that contains a negatively charged polyatomic ion containing oxygen usually has a name ending in –ate.

- Fixed composition of compounds

ü  A compound is made up of different elements chemically combined in a fixed ratio.

ü  For example, water (H₂O) is a compound made only by joining together 2 atoms of hydrogen to one atom of oxygen.

ü  That is, the ratio of hydrogen atoms to oxygen atoms in water is always 2 : 1.

Mixtures

- What are mixtures?

ü  Mixtures are formed when 2 or more substances are added together without chemical bonds being formed.

ü  Examples of mixtures include muddy water and air.

ü  Air is made up of gases such as nitrogen and oxygen mixed together.

- Different types of mixtures

ü  The ratios of the components of mixture are not fixed. They can be present in any ratio.

ü  A mixture can exist in various ways :

- 2 elements

- A mixture of 2 compounds

- A mixture of 1 element and 1 compound

- Comparison of Mixtures with Compounds

ü  Separation

Mixture	Compound
The components of a mixture can be separated by physical methods, eg filtration, distillation or chromatography.	The elements in a compound can only be separated by chemical reactions or by using electricity.

ü  Properties

Mixture	Compound
The chemical properties of a mixture are the same as those of its components.	The physical and chemical properties of a compound are different from those of the elements in the compound.

ü  Energy Changes

Mixture	Compound
No chemical reaction takes place when a mixture is formed – usually there is little or no energy change.	A chemical reaction takes place when a compound is formed – usually there is an energy change, eg, the reactants get hot.

ü  Composition

Mixture	Compound
The components of a mixture can be mixed in any proportion.	The elements in a compound are always combined in a fixed proportion (by mass).

Changes

- Physical Change

ü  No new substance formed

ü  Usually easily reversible

ü  May or may not involve heating

- Chemical Change

ü  New chemical substance(s) is/are formed

ü  Usually irreversible (some chemical changes can be reversed under special conditions)

ü  Heat energy may be given off or absorbed

ü  Light energy may be given off or absorbed

- Signs of a chemical change

ü  A change in colour

ü  Production of a gas

ü  Formation of a precipitate from mixing solutions

ü  Change of temperatures

ü  ALL THE ABOVE MUST FOLLOW THE FORMATION OF A NEW CHEMICAL SUBSTANCE

- Chemical reactions

ü  A process in which new chemical substance is formed

ü  New chemical substances formed due to rearrangement of atoms

ü  No atoms are created or destroyed, according to the Law of Constant Mass

Reactant à Products

Types of chemical reactions

- Combination (Synthesis)

ü  Two or more substances combine to form a new substance (magnesium + oxygen à magnesium oxide)

- Decomposition

ü  A substance breaks down into two or more simpler substances (calcium carbonate → calcium oxide + carbon dioxide)

3. Combustion of burning

ü  Combination of a substance with oxygen.

ü  Heat and light energy are given off (hydrocarbon + oxygen → carbon dioxide + water)

4. Displacement Reaction

ü  A chemical reaction with an atom / a group of atoms get replaced by another atom / group of atoms (hydrogen bromide + chlorine → hydrogen chloride + bromine)