Mixtures Flashcards – AQA GCSE Combined Science: Trilogy (8464) — Chemistry — Foundation

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 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 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 filtered?

It is poured through filter paper, usually held in a funnel.

In filtration, what are the filtrate and residue?

The filtrate is the liquid collected after passing through the paper; the residue is the insoluble solid retained on it.

What happens to a substance dissolved in a liquid during filtration?

It passes through the filter paper with the liquid.

What is crystallisation used to obtain?

A dissolved solid from a solution, as crystals.

What are the main stages of crystallisation?

1. Evaporate some solvent to concentrate the solution.
2. Leave the solution to cool so crystals form.
3. Separate the crystals from the remaining solution and dry them.

Does crystallisation create a new substance?

No. It is a physical separation process.

What is paper chromatography used to separate?

Dissolved substances in a mixture.

What are the main steps in carrying out paper chromatography?

1. Place a small spot of the mixture on a pencil baseline near the bottom of the paper.
2. Place the paper in solvent, keeping the spot above the solvent level.
3. Let the solvent move up the paper, carrying the substances with it.

Why do substances travel different distances in paper chromatography?

They have different solubilities in the solvent and different attractions to the paper.