8.1.1 Pure substances
In Chemistry, pure substance is…
- Single element or compound
- Not mixed with any other substance
- Eg vaporised iodine
Pure elements and compounds
- Melt & boil at specific temp
- Melting & boiling point data → distinguish pure substances from mixtures
In everyday language, pure substance is…
- Substance that has had nothing added to it
- Unadulterated & in its natural state
- Eg pure milk
8.1.2 Formulations
Formulations
- Mixture that has been designed as a useful product
- Made by mixing components in carefully measured quantities → ensure product has the required properties
- Eg fuels, cleaning agents, paints, medicines, alloys, fertilisers & foods
8.1.3 Chromatography
What is chromatography used for?
To separate mixtures & give info to help identify substance
How to set up?
- Draw a pencil line on the paper.
- Place ink on the baseline in a dot.
- Place the paper into the beaker which has water in it. Make sure the baseline is above water level so dye doesn’t dissolve in water.
- Hang paper over edge of beaker to keep it right.
- Put a lid on coz H2O(s) ⇌ H2O(g) & lid → closed reaction
- Wait for solvent to go up paper near the top.
- Remove paper & let it dry.
- Draw circles around spots.
Describe the results
- A is made up of 1 dye
- B is made up of 1 dye
- C is made up of 1 dye
- A & C matches the colouring from cake icing
Calculate the distance moved by the solvent (2)
Explain how different dyes are separated by paper chromatography. (4)
- Solvent moves through paper
- Different dyes have different solubility in solvent & different attractions for paper
- So they are carried to different distances
Why do different compounds separate in a gas chromatograph column? (1)
- Different substances travel at different speeds
Identify the errors & describe problem each error would cause (4)
- Baseline drawn in ink – dissolves in solvent
- Dye under solvent – dissolves in solvent
- Water level above start line
- Food colours would dissolve into water
- Start line drawn in ink
- Ink would ‘run’ on the paper