How does a pure substance differ from a mixture in melting and boiling points?
Pure substance: Fixed melting and boiling points.
Mixture: Melts and boils over a range of temperatures.
What is simple distillation used for?
To separate a solvent from a solution (e.g. water from salt solution).
How does it work?
The solvent evaporates, condenses, and is collected.
What is fractional distillation used for?
To separate liquids with different boiling points (e.g. ethanol and water).
How does fractional distillation work?
The mixture is heated; liquids boil at different temperatures and condense separately.
What is filtration used for?
To separate an insoluble solid from a liquid (e.g. sand from water).
What is crystallisation used for?
To obtain crystals of a soluble solid from a solution by evaporating some solvent.
What is paper chromatography used for?
To separate and identify substances in a mixture (e.g. dyes, inks).
What does a chromatogram show?
Spots at different heights represent different components of a mixture.
What does one spot mean in a chromatogram?
The substance is pure.
What is the formula for the Rf value in chromatography?
Rf = distance moved by substance ÷ distance moved by solvent front
What is the Rf value used for?
To identify substances by comparing with known Rf values.
How do you investigate paper chromatography practically?
Draw a pencil baseline and add ink/food colouring spots.
Place paper in solvent (below the line).
Let solvent rise and separate the colours.
Measure distances to calculate Rf values.
