2.2 Separating Substances

Completely made up of a single element or compound

More than one compound or element present

A pure substance will have a sharp melting point and a mixture will melt over a range of temperatures

Use melting point apparatus: it will heat up the sample very slowly so you can observe and record the exact temperature it melts at

A mixture of liquids with very different boiling points

1- Pour your solution into a flask 2- Raise the flask with a thenometer in it above a Bunsen burner. Connect a condenser to the flask which flows into a beaker 3- Gradually heat the flask until the part of the solution with the lowest boiling point evaporates 4- The water vapour passes into the condenser where it cools and condenses and flows into the beaker to be collected

A mixture of liquids with similar boiling points

1- Put your mixture in a flask 2- Attatch a fractionating column with a thenometer above the flask, connected to a condenser which flows into different test tubes on a test tube rack 3- Gradually heat the flask until the liquid with the lowest boiling point evaporates and will slowly make its way to the top of the collumn where it flows into the condenser condenses and falls into the beaker 4- Liquids with higher boiling points might start to evaporate but they will condense before the top of the collumn because it is cooler there 5- Once the first liquid has been collected raise the temperature until the next one reaches the top

Glass column filled with glass rods which is hotter at the bottom and cooler at the top

An insoluble solid from a liquid

1-Put some filter paper into a funnel above a beaker 2- Pour your mixture into it. The liquid part of the mixture runs through the paper leaving solid residue

A soluble solid from a solution

1- Pour the solution into an evaporating dish and gently heat it above a Bunsen burner. Some liquid will start to evaporate and the solution will become more concentrated 2- Once crystals start to form remove the dish from the heat and allow the solution to cool 3- Insoluble crystals should form 4- Filter them from the solution and pat them dry

A mixture of soluble substances and identifies them too

Where the molecules can move

Where the molecules can’t move

Liquid or gas

Solid or really thick liquid

The solvent

The filter paper

1- Draw the baseline near the bottom of the paper. Put a spot of mixture to be separated on the line. 2- Put some of the solvent into a beaker. Dip the bottom of the paper (but not the spot) into the solvent 3- Put a watch glass on the beaker 4- The solvent will start to move up the paper. When the solvent reaches the chemicals in the mixture they will move up too. 5- You will see different chemicals in the sample separate out 6- Remove the paper from the beaker before the solvent reaches the top and mark the solvent front

The line where the mixture starts in chromatography

Pencil marks are insoluble and so won’t move with the solvent as the ink might

The line marking the distance the solvent has moved