Element, compound and mixtures

Question 1

Element

Answer 1

A substance is made up of atoms that all contain the same number of protons (one type of atom) and cannot be split into anything simpler. Examples: hydrogen, oxygen, carbon

Question 2

Compound

Answer 2

A pure substance is made up of two or more elements chemically combined together. There are unlimited types of compounds. Cannot be separated by physical methods of separation. Example: copper (II) sulphate, calcium carbonate

Question 3

Mixture

Answer 3

A combination of two or more substances (elements and/or compounds) that are not chemically joined together. Can be separated by physical method of separation. Examples: salt and water, air

Question 4

Atoms

Answer 4

The smallest particles of an element that consists of electrons surrounding a nucleus that contains protons and neutrons

Question 5

Molecule

Answer 5

A group of two or more atoms chemically joined together forming an identifiable unit which retains the properties and composition of the substance

Question 6

Filtration

Answer 6

Separating insoluble solid from a liquid. The filtrate passes through and the insoluble solid (residue) stays in the filter paper

Question 7

Simple distillation

Answer 7

Separating a solvent from a solution. Method for separating substances with very different boiling points

Question 8

Fractional distillation

Answer 8

Water goes in at the bottom to ensure the jacket of the condenser is full of water. Method for separating substances with similar but different boiling points. The lower boiling point substance will come off first

Question 9

Crystallisation

Answer 9

Is used to produce solid crystals from a solution. Heat solution to evaporate some of the water until crystals form

Question 10

Chromatography

Answer 10

Is used to separate substances that have different solubilities in a given solvent (e.g. different coloured inks that have been mixed to make black ink)

Question 11

Chromatography practical

Answer 11

• Spot the ink / food colouring samples on a pencil line on the paper (pencil is used not ink – ink would dissolve in the solvent and pencil is insoluble.)
• Place the paper in beaker containing the solvent with solvent level below the spots (this prevents the spots mixing / dissolving in the solvent.)
• Cover the container with a lid – prevents evaporation of solvent and risk of fire
  if the solvent is not water (fumes may also be toxic.)
• Leave until the solvent reaches near the top of the paper.
• Remove the paper and allow it to dry.

If a coloured substance does not move up the paper it means it is insoluble in the water/solvent.