Properties of compounds
It is important to know the properties of compounds in a mixture as each property can be linked to a purification technique.
Solubility
Some properties are visible to the naked eye, like insoluble compounds or solids in a mixture - known as a suspension. When a solute is soluble in a solvent then the resulting solution may change color. When a solute is soluble in water, we often show that in the chemical name. Eg. MgSO4·7H2O.
Miscibility
Another property visible to the naked eye is immiscibility - when two liquids do not mix and form a boundary layer. Oil and water do not mix, because the former is hydrophobic and the latter hydrophilic. While bodies of water can be immiscible because of differences in their density, temperature and salinity.
Volatility/Boiling points
After simple tests or analyses, we can estimate the volatility or boiling point of a compound. Simple, organic compounds like alcohols mean they are highly volatile and so have low boiling points. This can be detected without any testing since we can smell alcohol at room temperature.
Other properties
More complex analyses, like NMR and mass spectrometry, can help reveal the chemical composition of compounds. From the chemical composition, we can estimate the molecular size and even predict the properties of the compounds. For example, if the compound is likely to be hydrophobic if it has large apolar regions, which is common in biomolecules.