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Chrome alum or Chromium(III) potassium sulfate is the potassium double sulfate of chromium. Its chemical formula is KCr(SO 4 ) 2 and it is commonly found in its dodecahydrate form as KCr(SO 4 ) 2 ·12(H 2 O).
The chromate coating process starts with a redox reaction between the hexavalent chromium and the metal. [2] In the case of aluminum, for example, Cr 6+ + Al 0 → Cr 3+ + Al 3+ The resulting trivalent cations react with hydroxide ions in water to form the corresponding hydroxides, or a solid solution of both hydroxides: Cr 3+ + 3 OH − → Cr ...
The most common of these analogs is chrome alum KCr(SO 4) 2 ·12 H 2 O. In most industries, the name "alum" (or "papermaker's alum") is used to refer to aluminium sulfate, Al 2 (SO 4) 3 · n H 2 O, which is used for most industrial flocculation [1]: 766 (the variable n is an integer whose size depends on the amount of water absorbed into the alum).
Chromium(III) can be obtained by dissolving elemental chromium in acids like hydrochloric acid or sulfuric acid, but it can also be formed through the reduction of chromium(VI) by cytochrome c7. [9] The Cr 3+ ion has a similar radius (63 pm) to Al 3+ (radius 50 pm), and they can replace each other in some compounds, such as in chrome alum and alum.
Chromium's ability to form such stable bridged bonds explains why it is considered one of the most effective tanning compounds. Chromium-tanned leather can contain between 4 and 5% of chromium. [16] This efficiency is characterized by its increased hydrothermal stability of the skin, and its resistance to shrinkage in heated water. [13]
Mordants include tannic acid, oxalic acid, [4] alum, chrome alum, sodium chloride, and certain salts of aluminium, chromium, copper, iron, iodine, potassium, sodium, tungsten, and tin. Iodine is often referred to as a mordant in Gram stains, but is in fact a trapping agent. [3] [failed verification]
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Chrome plating (less commonly chromium plating) is a technique of electroplating a thin layer of chromium onto a metal object. A chrome plated part is called chrome, or is said to have been chromed. The chromium layer can be decorative, provide corrosion resistance, facilitate cleaning, and increase surface hardness. Sometimes a less expensive ...