1.8: Understand How to Classify a Substance as an Element, Compound or Mixture

CLASSIFICATIONS:

s

CLASS	DEFINITION
ELEMENT	Substance made up of Atoms that all contain the same number of Protons (one type of Atom) and cannot be split into anything simpler Example: Hydrogen, Oxygen, Carbon
COMPOUND	Substance made up of two or more Elements chemically combined together Example: Copper (II) Sulphate, Calcium Carbonate
MIXTURE	Combination of two or more substances (Elements and / or Compounds) that are not chemically joined together Example: Sand and Water, Oil and Water

Example:

s

1.9: Understand that a Pure Substance has a Fixed Melting and Boiling Point, but that a Mixture may Melt or Boil Over a Range of Temperatures

PURE SUBSTANCE: Contains only one substance with no other substances mixed together

s

• As all molecules of the same substance have the same melting and boiling point, pure substance has fixed melting and boiling point

MIXTURE: Combination of two or more substances (Elements and / or Compounds) that are not chemically joined together

s

• As mixture contains different substances that have different melting and boiling point, they will have range of melting and boiling point

1.10: Describe these Experimental Techniques for the Separation of Mixtures: Simple Distillation, Fractional Distillation, Filtration, Crystallization, Paper Chromatography

SIMPLE DISTILLATION

Diagram showing the Simple Distillation of a Mixture of Salt and Water

USE: To separate a liquid from a solution (E.g Water from a Solution of Salt Water)

EXPLANATION: Solution is heated and Water vapors will rise and evaporate Water vapors pass through condenser where it cools and condenses, turning into a liquid that is collected in a beaker After all Water is evaporated from solution, solute will be left behind

FRACTIONAL DISTILLATION

Diagram showing the Fractional Distillation of a Mixture of Ethanol and Water

USE: To separate two or more liquids that are miscible with one another (E.g Ethanol and Water from a Mixture of the Two)

EXPLANATION: Solution is heated to temperature of substance with the lowest boiling point and vapors of this substance will rise and evaporate Vapors pass through condenser where it cools and condenses, turning into a liquid that is collected in a beaker After all of substance is evaporated and collected, mixture of substance will be left behind

FILTRATION

Diagram showing the Filtration of a Mixture of Sand and Water

USE: To separate an undissolved solid from a mixture of the solid and a liquid / solution ( E.g Sand from a mixture of Sand and Water)

EXPLANATION: Filter paper is placed in a filter funnel, which is placed above another beaker Mixture of insoluble solid and liquid is poured into filter funnel, which only allows small liquid particles to pass through as filtrate Solid particles are too large to pass through as filtrate so will stay behind as residue

CRYSTALLIZATION

Diagram showing the Process of Crystallization

USE: To separate a dissolved solid from a solution (when the solid is more soluble in hot solvent than in cold) (E.g Copper (II) Sulphate from a Solution of Copper (II) Sulphate in Water)

EXPLANATION: Solution is heated, allowing solvent to evaporate and leave saturated solution Saturated solution is left to cool, and solids will come out of solution to grow into Crystals Crystals are collected and allowed to dry

PAPER CHROMATOGRAPHY

Diagram showing the Paper Chromatography of Ink and Plant Dye

USE: To separate substances that have different solubilities in a given solvent (E.g Different coloured inks mixed to form black ink)

EXPLANATION: Pencil line is drawn on chromatography paper and concentrated spot of ink/dye is placed on it Paper is lowered into bucket of solvent, allowing solvent to travel up the paper taking particles of coloured substance with it Different substances have different solubilities so will travel at different rates, causing substance to be spread along vertical length of paper This will show the different components of the ink/dye

1.11: Understand How a Chromatogram Provides Information about the Composition of a Mixture

PAPER CHROMATOGRAPHY - COMPOSITION OF A MIXTURE

Diagram showing the Composition of an Ink using Paper Chromatography

COMPOSITION OF A MIXTURE: Chromatogram shows the composition of mixture as different coloured substances (components) and will spread apart as they have different solubilities so will travel at different rates Pure susbtance will only produce one spot on chromatogram during paper chromatography In the diagram above, Red, Blue, and Yellow are three pure substances, whilst sample on left is a mixture of all three

1.12: Understand How to Use the Calculation of Rf Values to Identify the Components of a Mixture

Rf VALUES: Used to identify the components of mixtures

s

• Rf value of a particular compound is always the same
• This allows industries to use chromatography to identify compounds in mixtures

EQUATION:

s

Rf Value =     Distance Moved by Compound    ÷     Distance Moved by Solvent

1.13: Practical: Investigate Paper Chromatography using Inks / Food Colourings

PAPER CHROMATOGRAPHY

Diagram showing the Paper Chromatography of Ink and Plant Dye

USE: To separate substances that have different solubilities in a given solvent (E.g Different coloured Inks mixed to form black ink)

METHOD: Pencil line is drawn on chromatography paper and a concentrated spot of ink/dye is placed on it PPaper is lowered into bucket of solvent, allowing solvent to travel up the paper taking particles of coloured substance with it Allow chromatography to occur until solvent reaches top of paper

RESULTS: As solvent travels up the paper, different substances have different solubilities so will travel at different rates, causing substances to spread apart This will show the different components of the ink/dye