TOPIC 2 – Experimental Techniques
· Appropriate apparatus for MEASURING:
- Time: stopwatch/clock
- Temperature: thermometer
- Mass: balance
- Volume: measuring cylinder, burette, pipette
· PAPER CHROMATOGRAPHY:
- Used to separate mixtures and give information to help identify substances.
- Involves a stationary phase and a mobile phase.
- Separation depends on the distribution of substances between the phases.
- To carry it out: place the substances on line near bottom of paper, place the paper in the solvent and
observe how far the substances travel up the paper.
·Interpreting chromatograms:
- If two substances are the same, they will show up the same on the paper.
- Pure substances will only produce one spot and impure substance (or a mixture) will produce two
or more spots because it will separate on the paper to show all the different components as
separate spots.
- You can analyse colourless mixtures of chemicals if the ‘spots’ can be coloured by a chemical or light
treatment; these are all known as locating agents.
· RF Values:
- RF Value = distance moved by substance ÷ distance moved by solvent
- Different compounds have different Rf values in different solvents, which can be used to help
identify the compounds.
- Compounds in a mixture may separate into different spots depending on the solvent but a pure
compound will produce a single spot in all solvents.
· PURITY OF SUBSTANCES:
- A pure substance = a single element or compound, not mixed with any other substance.
- Pure substances melt and boil at specific temperatures.
- Mixture melt over a range of temperatures due to them consisting of 2 or more elements/compounds.
- To have a pure substance for food or drugs is very important as impurities could be dangerous even in
small amounts.
· Appropriate apparatus for MEASURING:
- Time: stopwatch/clock
- Temperature: thermometer
- Mass: balance
- Volume: measuring cylinder, burette, pipette
· PAPER CHROMATOGRAPHY:
- Used to separate mixtures and give information to help identify substances.
- Involves a stationary phase and a mobile phase.
- Separation depends on the distribution of substances between the phases.
- To carry it out: place the substances on line near bottom of paper, place the paper in the solvent and
observe how far the substances travel up the paper.
·Interpreting chromatograms:
- If two substances are the same, they will show up the same on the paper.
- Pure substances will only produce one spot and impure substance (or a mixture) will produce two
or more spots because it will separate on the paper to show all the different components as
separate spots.
- You can analyse colourless mixtures of chemicals if the ‘spots’ can be coloured by a chemical or light
treatment; these are all known as locating agents.
· RF Values:
- RF Value = distance moved by substance ÷ distance moved by solvent
- Different compounds have different Rf values in different solvents, which can be used to help
identify the compounds.
- Compounds in a mixture may separate into different spots depending on the solvent but a pure
compound will produce a single spot in all solvents.
· PURITY OF SUBSTANCES:
- A pure substance = a single element or compound, not mixed with any other substance.
- Pure substances melt and boil at specific temperatures.
- Mixture melt over a range of temperatures due to them consisting of 2 or more elements/compounds.
- To have a pure substance for food or drugs is very important as impurities could be dangerous even in
small amounts.
