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Separating Mixtures - Coggle Diagram
Separating Mixtures
The Need for Separating Mixtures
To study the properties
To obtain useful substances
To avoid unwanted consequences
Methods
For Solid-Solid Mixtures
Sublimation
What is it?
Used when one of the solid substances can sublime when heating
Application
Used in printing processes
Magnetic Attraction
What is it?
Used to separate magnetic materials from non-magnetic materials
Application
At Scrap Yards, Mining and Hospitals
For Solid-Liquid Mixtures
Filtration
Purpose
Used to separate an insoluble solid from a liquid
Key Words
Residue
an insoluble solid that remains on the filter paper
Filtrate
liquid that passes through the filter paper
Evaporation
Purpose
Used to separate an dissolved solid from a solution by heating the solution to dryness
Condition
Only to be used if the dissolved solid is a heat-stable substance
Process
Step 1
The solution in the evaporating dish is heated up until the solvent has dried it up completely
Step 2
Dried salt crystals are collected in the evaporating dish
Crystalisation
Purpose
Used to separate a soluble solid from a solution
Condition
To be used if the solution is not heat-stable
otherwise, the solution will
Decompose on strong heating
Process
Step 1
The salt solution is filtered to remove any solid impurities
Step 2
The filtrate is heated to remove most of the solvent until the solution becomes saturated
Step 3
The saturated solution is left to cool gradually to allow the formation of large-size crystals
Step 4
The crystals are filtered and washed with little cold distilled water to remove impurities. They are then dried between filter paper
Chromatography
Purpose
To separate and identify small amount of substances that are dissolved in a solvent, such as dyes in coloured ink.
Usefulness
Test the purity of a substance
Identify the contents of a mixture
Advantages
Only a small amount of sample is required
Gives a fast and accurate analysis of a sample
Able to separate complex mixtures such as food dyes
Principle
Different solubility in a solvent
Causes the components to move at different speeds
Process
Step 2
The chromatographic paper is placed inside a beaker containing a solvent
Note
The solvent is below the starting line
Step 3
As the solvent moves up the paper, it separates the sample into its respective components
Step 1
A small amount of concentrated sample is placed on the starting line of a chromatographic paper
Step 4
The chromatographic paper is removed before the solvent reaches the edge of the other end of the paper
Precautions
Use fine capillary tubes to place a small and concentrated sample on the paper
How it would affect the result
Prevents the overlapping of components so that clear and distinct lines or spots can be obtained
Solvent should be below the starting line
How it would affect the result
This prevents the sample from dissolving into the solvent so that it can travel up the paper
Draw the starting line with a pencil
How it would affect the result
A pencil is an element, so it is not made up of dyes and will not be separated by the solvent to interfere with the results
Solvent front should be as high as possible
How it would affect the result
It ensures that the components in a sample are fully separated
Jar should be covered with a lid when a volatile solvent is used
How it would affect the result
Prevents the solvent from evaporating too fast
Ensures that the jar is saturated with solvent vapour
Simple Distillation
Purpose
Used to separate a liquid from a solid-liquid mixture
Features
Boiling Stones
Smoothen boiling by reducing bumping of liquid during boiling
Prevents overheating of the liquid being distilled
Thermometer
Placed near the opening of the condenser to measure the temperature of the vapour accurately
Condenser
Ensures that the coldest part of the condenser is present before the vapour escapes
Conical Flask
Used as the receiving flask
The narrow neck of the flask can reduce loss of the distillate through splashing
For Liquid-Liquid Mixtures
Fractional Distillation
Used to separate two or more miscible liquids in a mixture
What are miscible liquids?
Liquids which dissolve in each other to form a single layer
The liquids have different boiling points hence we can separate them
How?
A liquid with a lower boiling point will be distilled first
What is the fractionating column for?
Allows a liquid of a higher boiling point to condense and fall back during the distillation of a substance of a lower boiling point.
Why?
This ensures a more efficient separation of the different liquids.
