Separation & Purification (Cambridge (CIE) IGCSE Chemistry)
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What is paper chromatography used for?
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What is paper chromatography used for?
Paper chromatography is used to separate substances that have different solubilities in a given solvent, such as identifying the components of a mixture.
What does a single spot on a chromatogram indicate?
A single spot on a chromatogram indicates that the substance is pure.
What should the base line on a chromatogram be drawn with?
The baseline on a chromatogram should be drawn with a pencil.
True or False?
The solvent level should start above the pencil line on a chromatogram.
False.
The solvent level should not start above the pencil line, as this would ruin the chromatogram.
How many substances are in sample D?
There are 3 substances in D.
True or False?
Multiple spots on a chromatogram indicate a pure substance.
False.
Multiple spots on a chromatogram indicate that the substance is a mixture.
True or False?
If two substances are the same, they will produce identical chromatograms.
True.
If two substances are the same, they will produce identical chromatograms.
Which colours from A-E does black food colouring contain?
The black food colouring contains A, E and an unknown.
Why should the baseline (starting line) in chromatography be drawn in pencil?
The baseline (starting line) should be drawn in pencil because it will not contaminate the results / will not run.
State the equation to calculate the retention factor (Rf value). (Extended tier only)
The equation for the retention factor (Rf value) is:
Rf =
What does an Rf value closer to 1 indicate? (Extended tier only)
An Rf value close to 1 indicates that the component is very / highly soluble in the solvent used.
True or False?
The Rf value of a compound is always the same, regardless of the solvent used. (Extended tier only)
False.
The Rf value of a compound depends on the solvent used.
If the solvent is changed, the Rf value will change.
What is the purpose of calculating Rf values in paper chromatography? (Extended tier only)
The purpose of calculating Rf values is to allow chemists to identify unknown substances.
What does the Rf value range between? (Extended tier only)
The Rf values ranges between 0 and 1.
Why does an Rf value have no units? (Extended tier only)
An Rf value does not have units because it is a ratio.
What are locating agents in chromatography used for? (Extended tier only)
Locating agents are used to identify colourless substances on a chromatogram.
What does simple distillation separate?
Simple distillation is used to separate:
a liquid and soluble solid from a solution (e.g., water from a solution of salt water)
a pure liquid from a mixture of liquids
State what is meant by the term simple distillation.
Simple distillation is a technique used to separate a liquid from a solution (e.g., water from a salt solution) by boiling the solution and condensing the vapour.
What is fractional distillation?
Fractional distillation is a technique used to separate two or more liquids that have different boiling points from a mixture.
What does filtration separate?
Filtration separates an undissolved solid from a mixture of solid and liquid.
What is crystallisation used for?
Crystallisation is used to separate a dissolved solid from a solution.
In terms of the solid (solute), what is important about the solvent?
It is important that the solid (solute) is more soluble in hot solvent than in cold.
How can melting and boiling points distinguish between pure substances and mixtures?
Pure substances have specific and sharp melting and boiling points, while mixtures have a range of melting and boiling points
True or False?
Salt dissolved in water is a pure substance.
False.
A solution of salt dissolved in water is a mixture.
True or false?
Impure substances have boiling points higher than the standard boiling point of the substance.
True.
Impure substances have boiling points higher than the standard boiling point of the substance.
True or false?
Impure substances have melting points higher than the standard melting point of the substance.
False.
Impure substances have melting points lower than the standard melting point of the substance.