Concept 6: Separating Mixtures
Success Criteria & Vocabulary
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I can identify different separation techniques.
I can describe and carry out magnetic separation.
I can describe and carry out decanting.
I can describe and carry out filtration.
I can describe and carry out evaporation.
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Complete Education Perfect:
Task called 'Separating Mixtures'.
Making Copper Sulfate Crystals using Filtration and Evaporation
Practical: Using Filtration and Evaporation to Make Copper Sulfate Crystals
Aim: To make copper sulfate crystals from copper carbonate and sulfuric acid.
Materials: Heatproof mat, boiling tube, evaporating dish, 250 mL beaker, funnel, filter paper, hot water, copper carbonate powder, sulfuric acid.
Collect the equipment.
Create a water bath, by pouring warm water into a 250 mL beaker.
Place 1 cm of sulfuric acid in a boiling tube and warm it in a water bath.
Add a spatula of copper carbonate powder to the acid and swirl to mix. Continue adding small amounts of copper carbonate powder until the reaction stops (no more bubbling). You want to have a supersaturated solution.
Fold the filter paper and place in the funnel. Filter the mixture to remove the excess carbonate.
Pour the filtrate (the copper sulfate solution) into an evaporating basin.
Pour the solution into an evaporating basin and place on the sunny window sill. Leave overnight to allow all the water to evaporate.
Concept 6: Support Notes
Since mixtures are combinations of elements and/or compounds that are NOT chemically joined together, all mixtures can be separated by physical separation techniques.
The state of the various substances in the mixture (such as a liquid and solid) or the physical properties of the substances (such as different boiling points) will determine which method of separation will be used.
Magnetic separation is when you use a magnet to separate a magnetic material from a non-magnetic material.
For example, you can use magnets to separate:
Iron from salt.
Iron from sand.
Decanting is simply pouring off a liquid without losing any of the denser substance (usually an insoluble solid) at the bottom of the container.
Decanting separates a heavier substance from a lighter one. Most of the time, the are interested to collect the substance at the BOTTOM of the container.
Decanting is also used to separate a liquid from an insoluble solid. Decanting is done by gently pouring a liquid from one container to another.
You may use a stirring rod to guide the liquid you are pouring.
We use filtration to separate an insoluble solid in a mixture from the liquid completely.
The solvent molecules (liquid) and any dissolved molecules present in the solution can pass through the filter paper, which has small holes, while the solid particles cannot because they are too large and stay in the filter paper.
The solvent or solution containing dissolved substances passes through the filter paper is called filtrate. The solid particles that remain on the filter paper are called the residue.
Evaporation by boiling separates a dissolved solid from a liquid. The solvent (liquid) is lost into the surroundings.
The liquid will evaporate but evaporation becomes faster at higher temperatures. The solid remains because it has a higher boiling point than the liquid.
Chromatography is a method used to separate the various coloured substances in a mixture of dye or ink.
There are two parts to a chromatograph: a stationary phase and a mobile phase.
The stationary phase doesn’t move. It’s the material on which you put the mixture.
The mobile phase is the solvent you use to sweep up the soluble components in the mixture.
The most soluble coloured compounds travel through the stationary phase fastest, while the least soluble coloured compounds travel through the stationary phase slowest.
Analyse the chromatogram to the right. For each mixture, which coloured compound is most soluble?
Summary of Separation Techniques
When two solid substances are mixed together, they can be separated by dissolving. A solvent such as water can be added if only one of the substances is soluble. For example, if salt is mixed with dirt, then adding water will dissolve the salt (which can later be separated by evaporation), and the remaining dirt can be removed from the solution by filtering. The salt becomes the solute and will go through the filter as it is in solution.
Magnetism can be used to separate a magnetic substance (such as iron) from a mixture containing non-magnetic substances (such as sulfur or sand).
The magnetic substance of the mixture is separated with the help of the magnetic attraction.
A magnet is moved over the mixture containing the magnetic substance (e.g. iron filings). These get attracted to the magnet. The process is repeated until the magnetic material is completely separated from the mixture. The non-magnetic substance is left behind.