How would you confirm that a colourless liquid is pure?

Question

How would you confirm that a colourless liquid is pure?

Answer 1

Depending on the liquid, you could measure its freezing (melting) point, or boiling point.  Pure compounds tend to have distinct temperatures.  Impure mixtures have a wider range for these temperatures.  Crystals are more perfect for pure compounds also.  These are rules of thumb, there are always exceptions.

More complex analytical methods would be liquid and gas chromatography, mass spectroscopy, fluorescence spectroscopy, absorption and emission spectroscopy, optical rotation spectroscopy.  These are the most common types of analysis I've done.