What should guide the choice of a separation or purification method?
The physical differences between the substances in the mixture.
AQA GCSE Combined Science: Trilogy (8464) — Chemistry — Higher · 5.1.1.2
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What should guide the choice of a separation or purification method?
The physical differences between the substances in the mixture.
Which method separates an insoluble solid from a liquid?
Filtration.
Which method obtains a dissolved solid from a solution?
Crystallisation.
Which method collects a solvent from a solution containing dissolved solids?
Simple distillation.
Which method separates a mixture of liquids with different boiling points?
Fractional distillation.
Which method separates dissolved substances that move differently in a solvent?
Chromatography.
What is a mixture?
Two or more elements or compounds together without being chemically bonded to each other.
What happens to the chemical properties of substances in a mixture?
Each substance retains its own chemical properties.
How can the substances in a mixture be separated?
By physical processes.
Does separating a mixture create new substances?
No. It only sorts out the substances already present.
What property allows distillation to separate substances?
Differences in boiling point.
What is the sequence of steps in simple distillation?
The substance with the lower boiling point vaporises first; its vapour is then cooled, condensed and collected.
What is a common use of simple distillation?
Obtaining a solvent from a solution.
What happens inside the fractionating column during fractional distillation?
Repeated vaporisation and condensation.
What is fractional distillation used to separate more effectively?
A mixture of liquids with different boiling points.
Are new substances made during distillation?
No. The substances are physically separated.
What does filtration separate?
An insoluble solid from a liquid.
How is a mixture passed through a filter during filtration?
It is poured through filter paper placed in a funnel.
What is the filtrate in filtration?
The liquid that passes through the filter paper.
What is the residue in filtration?
The solid retained by the filter paper.
Is filtration a physical or chemical separation, and does it produce a new substance?
It is a physical separation and produces no new substance.
What does crystallisation separate from a solution?
A dissolved solid, by forming solid crystals.
What are the main steps in crystallisation?
Why is crystallisation a physical separation?
The dissolved substance becomes solid again without forming a new substance.
Why can paper chromatography separate dissolved substances?
They travel at different rates with the solvent through the paper, forming separate spots.
What determines how a substance moves during paper chromatography?
Its relative attraction to the solvent and the paper.
How is the mixture positioned on the paper before chromatography begins?
A small spot is placed on a pencil baseline above the solvent level.
Does paper chromatography produce new substances?
No. The separation is physical.