Potassium alum
From Free net encyclopedia
Potassium alum or potash alum is the potassium double sulfate of aluminium. Its chemical formula is KAl(SO4)2 and is commonly found in its dodecahydrate form as KAl(SO4)2·12(H2O). It is commonly used in water purification, leather tanning, fireproof textiles, and baking powder. Its mineral form is known as kalunite (rock form) and kalinite (fiber form).
Characteristics
- Melting Point: 92-93 °C
- Boiling Point: 200 °C (decomposes)
- Density: 1.76 g/cm3
- Atomic mass: 258.207
- Color: Clear (with whitish tinge)
Potassium alum, K2SO4·Al2(SO4)3·24H2O, crystallizes in regular octahedra (similar to two pyramids stuck together, but with flattened corners). and is very soluble in water. The solution reddens litmus and is an astringent. When heated to nearly a red heat it gives a porous, friable mass which is known as "burnt alum." It fuses at 92 °C in its own water of crystallization. "Neutral alum" is obtained by the addition of as much sodium carbonate to a solution of alum as will begin to cause the separation of alumina; it is much used in mordanting. Alum finds application as a mordant, in the preparation of lakes for sizing hand-made paper and in the clarifying of turbid liquids. See the mineral alunite.
Mineral form and occurrence
Potassium alum is a naturally occurring sulfate mineral which typically occurs as encrustations on rocks in areas of weathering and oxidation of sulfide minerals and potassium-bearing minerals. Alunite is an associate and likely potassium and aluminium source. Found at Vesuvius, Italy, Alum Cave, Tennessee, and Alum Gulch, Arizona in the United States.
External links
Template:Mineral-stubru:Алюмокалиевые квасцы vi:Kali alum zh:鉀鋁礬