Separating Mixtures

MIXTURES

• Mixtures AND Compounds are both combinations of TWO or MORE SUBSTANCES.
• COMPOUNDS are combinations of two or more substances that are CHEMICALLY COMBINED.
• MIXTURES are combinations of two or more substances that are NOT CHEMICALLY COMBINED.
• The substances in a mixture can be both ELEMENTS or COMPOUNDS, and they RETAIN their individual PROPERTIES.
• Compounds can only be separated using CHEMICAL REACTIONS.
• Mixtures can be separate using PHYSICAL METHODS.

 

SEPARATING MIXTURES

The components of mixtures can often be separated more easily than compounds because they are NOT CHEMICALLY BONDED.

Examples of Physical Separation Techniques include:

• FILTRATION
• EVAPORATION
• CRYSTALLISATION
• SIMPLE DISTILLATION
• FRACTIONAL DISTILLATION
• CHROMATOGRAPHY

 

1. FILTRATION:

FILTRATION is a method used to separate an INSOLUBLE SOLID from a liquid. This can be particularly useful for removing solid impurities from a reaction mixture or product.

• The process involves pouring the mixture through a FILTER PAPER, where the solid is trapped and the liquid passes through.

 

 

2. EVAPORATION & CRYSTALLISATION:

• SOLUBLE SOLIDS, like salt, can be dissolved in a SOLVENT and then recovered by EVAPORATION or CRYSTALLISATION.

a) Evaporation:

• Pour the solution into an EVAPORATING DISH and gently heat it.
• As the solvent evaporates, the solution becomes more concentrated, and eventually, dry crystals will form.
• This method is best used when the substance DOES NOT DECOMPOSE upon heating.

b) Crystallisation:

• Similar to evaporation, start with a solution in an evaporating dish.
• HEAT gently until crystals start to form, indicating that the solution has become saturated.
• Allow the solution to COOL, which causes the formation of more crystals.
• Filter out the crystals and leave them to DRY in a warm place.

 

3. DISTILLATION:

a) Simple Distillation:

• SIMPLE DISTILLATION is a process to separate a LIQUID from a solution, often used when the liquids have different BOILING POINTS.
• During distillation, the solution is heated to the temperature of the LOWEST BOILING POINT. This causes the component with the lower boiling point to EVAPORATE.
• The vapour is then COOLED in a CONDENSER and collected as a liquid, leaving the component with the higher boiling point behind.
• This method is ideal for purifying water from seawater or separating a liquid product from a reaction mixture.

 

b) Fractional Distillation:

• FRACTIONAL DISTILLATION is used when you have a mixture of MORE THAN TWO liquids that have different boiling points.
• It involves using a FRACTIONATING COLUMN with glass rods in it, which allows substances with different boiling points to separate effectively. It creates a TEMPERATURE GRADIENT where the temperature is HIGH at the BOTTOM and LOW at the TOP.

• As the vapour of the mixture rises, the temperature cools down which causes the components with HIGHER BOILING POINTS to CONDENSE and fall back into the flask.
• The component with the LOWEST BOILING POINT will rise and condense into liquid and get collected in the beaker.
• The process is repeated, raising the temperature gradually to collect other liquids at different boiling points.

 

4. CHROMATOGRAPHY:

• CHROMATOGRAPHY is a method used to separate and analyse the components of a mixture.
• In paper chromatography, substances move at different rates, allowing them to be separated based on their solubility.
• It can be used to separate out the DYES in an INK.

How to Perform Paper Chromatography:

• Draw a line near the bottom of the filter paper with a pencil, as pencil marks are INSOLUBLE.
• Place a spot of the substance to be separated on the line.
• Use a suitable SOLVENT, such as water or ethanol, depending on the substances.
• Ensure the spot does not touch the solvent when you place the filter paper in the beaker.
• The solvent will move up the paper, taking the substances with it.
• Different substances in the mixture will travel at different speeds, resulting in separate spots.
• Once the solvent has nearly reached the top, remove the paper and let it dry to see the CHROMATOGRAM.