1.1.5 Mixtures

Example:

• Powdered iron and powdered sulfur mixed together form a mixture of iron and sulfur.
• They can be separated from each other without a chemical reaction, just like different colored sweets can be picked out from a mixed packet and sorted into separate piles.

Types of Substances:

• Element: A substance made up of only one type of atom.
• Compound: A substance where atoms of different elements are chemically joined.
• Mixture of Elements: A physical combination of different elements, not chemically bonded.
• Mixture of Elements and Compounds: A physical combination of both elements and compounds.

Separation of Mixtures:

Atoms/molecules in mixtures can be easily separated by physical processes such as:

1. Filtration
2. Evaporation
3. Chromatography
4. Distillation

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1. Filtration

Insoluble Solid from Liquid

Filtration is used to separate an insoluble solid from a liquid. (An insoluble substance is one that does not dissolve).

Example:

Sand can be separated from a mixture of sand and water using filtration. This is because sand does not dissolve in water.

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2. Evaporation

Soluble Solid from Liquid

Evaporation is used to separate a soluble solid from a liquid (a soluble substance does dissolve to form a solution).

Example:

Copper sulfate crystals can be separated from a copper sulfate solution using evaporation. It's important to remember that it is the water that evaporates away, not the solution itself.

3. Chromatography

Separating Liquids Due to Mass

Chromatography can be used to separate mixtures of coloured compounds. Mixtures that are suitable for separation by chromatography include inks, dyes, and colouring agents in food.

$R_f$ Values:

Different chromatograms and the separated components of the mixtures can be identified by calculating the $R_f$ value using the equation:

$$R_f = \frac{\text{distance moved by the compound}}{\text{distance moved by the solvent}}$$

The $R_f$ value of a particular compound is always the same if the chromatography is carried out in the same way. This consistency allows industries to use chromatography to identify compounds in mixtures.

Distillation

Separating Liquids Due to Boiling Point

Distillation is used for separating water and miscible liquids.

• Pure liquids have specific boiling points. For example, water boils at 100°C and ethanol boils at 78°C.
• Water and ethanol are miscible (they mix together easily without separating into layers).