Elements, compounds and mixtures 1.8-1.13

Consist of one type of atom only

A substance that is made of two or more different elements which are chemically bonded together e.g. a chemical reaction to form a molecule of carbon dioxide Difficult to separate the original elements out again Properties of a compound are often different from the original elements

No chemical bond between the different parts of a mixture - can be separated out physically Properties of a mixture are mixture of the properties of the separate parts Isn’t a pure substance - not made up of a single element or compound Therefore will melt or boil gradually over a range of temperatures

Fixed melting and boiling point

NO A mixture is not pure so it will melt or boil gradually over a range of temperatures

• Separate an insoluble solid from a liquid E.g. if the product of a reaction is an insoluble solid you can filter it out from the liquid reaction mixture • Purification –> solid impurities

Put a filter paper in a cone shape into a funnel and pour your mixture into it Liquid part runs through and leaves the solid residue behind

Separate a soluble solid from a solution

Pour the solution into an evaporating dish and gently heat the solution –> some water evaporate = solution more concentrated Remove from heat when some of the water has evaporated and leave to cool Salt should start to form crystals Filter the crystals out of the solution and leave them in a warm place to dry

• Draw a pencil line near the bottom of a sheet of filter paper • Add spots of different inks on the line at regular intervals • Loosely roll the sheet up and put it in a beaker of solvent (depending on what is being tested - water/ethanol) above the pencil line • Place a lid to stop the solvent evaporating • The solvent seeps up the paper with the inks • Each dye will move up the paper at a different rate and form a spot in a different place • Take out the paper when the solvent has nearly reached the top of the paper • End result is a chromatogram

• Different dyes will move up the paper at different rates • Some stick to the paper and others will dissolve more readily in the solvent (travel more quickly) • The distance the dyes travel depends on the solvent and the paper used

The ratio between the distance travelled by the dissolved substance (solute) and the distance travelled by the solvent

Rf = distance travelled by solute/distance travelled by solvent

Distance travelled - measure from the baseline to the centre of the spot

• Separate mixtures • Identify the substances present in a mixture –> if 2 inks have spots at the same distance they both contain that substance

Separate out solutions

• Solution is heated - part of the solution that has the lowest boiling point evaporates • Vapour is then cooled, condenses and collected • The rest of the solution is left in the flask

Can only separate things with very different boiling points

Separate a mixture of liquids

• Put the mixture in the flask with a fractionating column on top and heat it • The different liquids have different boiling points so evaporate at different temperatures • Liquid with the lowest boiling point evaporates first –> temperature at its boiling point it reaches the top of the column (cooler at the top of the column) • Higher boiling points liquids condense before reaching the top therefore • Once the first liquid has been collected raise the temperature