Chemical formula: (NH4)2Fe(SO4)2.6H2O
Synonyms: ammonium ferrous sulphate hexahydrate, ammonium iron (II) sulphate, ferrous ammonium sulphate.
Amount: 100 g
Appearance and odour: a mixture of small and medium light green crystals, slightly moist, without appreciable odour.
Packaging: professional wide necked, white HDPE bottle with blue conical seal cap and tamper evidence ring. Labelled. Bottle and cap are UN approved and reusable.
Description and uses: a double salt of ammonium sulphate and ferrous sulphate it is a primary source of a soluble iron (II) (ferrous) salt. Well soluble in cold water and highly soluble in hot water it is an ideal substance for crystal growing.
Named after Karl Friedrich Mohr, the German chemist who invented it, Mohr’s Salt is much more resistant to oxidation than plain ferrous sulphate (FeSO4) due to the presence of acidifying ammonium ions.
As a highly stable iron (II) compound with a high gravitational lever and a medium reducer it is often used as a titrant solution (0.1; 0.05 or 0.01 N) in redox titrations. For such analytical purposes it is recommendable (but not strictly speaking necessary) to dry the material overnight on filter paper in a dry, cool place. For most purposes ferrous ammonium sulphate titrant solutions require standardising.
To prevent hydrolysis (cloudiness) solutions of Mohr’s Salt are best prepared in 0.1 M strong acid (sulphuric or hydrochloric).