Elements, compounds and mixtures paper 2

Question 1

what is an element

Answer 1

The simplest type of substances made up of only one type of atom.

Question 2

what is a compound

Answer 2

A substance that contains two or more elements chemically joined together in fixed proportions.

Question 3

what is a mixture

Answer 3

Different substances in the same space, but not chemically combined

Question 4

Pure substances melting and boiling point

Answer 4

are fixed

Question 5

Mixture melting and boiling point

Answer 5

are over a wide range of temperatures

Question 6

Simple distillation

Answer 6

This method is used to separate a liquid from a solution. The salt water is boiled. The water vapour condenses back into a liquid when passed through the condenser. The salt is left behind in the flask.

Question 7

Fractional distillation

Answer 7

This method is used to separate a mixture of different liquids that have different boiling points.
By using the thermometer to carefully control of temperature of the column, keeping it at a certain temperature, only one substance remains as vapour all the way up to the top of the column and passes into the condenser.

The vapour then condense back into a liquid.

Question 8

Filtration

Answer 8

This method is used to separate an insoluble solid from a liquid.

The mixture is poured into the filter paper. The sand does not pass through and is left behind (residue) but the water passes through the filter paper and is collected in the conical flask (filtrate).

Question 9

Crystallisation

Answer 9

Gently heat the solution in an evaporating basin
until crystals form on a glass rod (which shows that a hot saturated solution has formed).
Leave to cool and crystallise.
Filter to remove the crystals.
Dry by leaving in a warm place.

Question 10

Paper chromatography

Answer 10

This method can be used to separate the parts of a mixture into their components.

Question 11

Rf value

Answer 11

distance of dye from baseline /distance of solvent front from the baseline

Question 12

practical: investigate paper chromatography using inks/food colourings

Answer 12

A pencil line (baseline) is drawn 1cm from the bottom of the paper
A spot of each sample of dye is dropped at different points along the baseline.
The paper is suspended in a beaker which contains a small amount of solvent. The bottom of the paper should be touching the solvent, but the baseline with the dyes should be above the level of the solvent.
A lid should cover the beaker
When the solvent has travelled to near the top of the paper, the paper is removed from the solvent and a pencil line drawn to show the level the solvent reached up the paper. This is called the solvent front.
The chromatogram is then left to dry so that all the solvent evaporates.