Aluminium chloride is usually assumed by chemists to be same as aluminium chloride anhydrous.
The definition of anhydrous is 'of a substance, especially a crystalline compound containing no water'. (Wikipedia 2017)
Aluminium chlorides (anhydrous) molar mass is 133.34 g/mol. It has no water attached to the ionic compound. Its chemical formula is usually shown as
However Aluminium chloride (hexahydrate) molar mass is 241.43 g/mol. This is because the Aluminium chloride absorbs water as it is hygroscopic (it absorbs water from the air), adding to its molar mass.
Its chemical formula is usually shown as