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Cobalt chloride is a common visual moisture indicator due to its distinct colour change when hydrated. The colour change is from some shade of blue when dry, to a pink when hydrated, although the shade of colour depends on the substrate and concentration.
Anhydrous cobalt(II) chloride is blue, while the hexahydrate is magenta in colour. [1] Because the color change of cobalt(II) chloride in different hydrates, it can be used to manufacture color-changing silica gel. Anhydrous cobalt halides react with nitric oxide at 70~120 °C to generate [Co(NO) 2 X] 2 (X = Cl, Br or I).
A humidity indicator card (HIC) is a card on which a moisture-sensitive chemical is impregnated such that it will change color when the indicated relative humidity (RH) is exceeded. This has usually been a blotting paper impregnated with cobalt(II) chloride base; Less toxic alternatives include other chemicals such as cobalt-free chloride base ...
Predicting the color of a compound can be extremely complicated. Some examples include: Cobalt chloride is pink or blue depending on the state of hydration (blue dry, pink with water) so it is used as a moisture indicator in silica gel. Zinc oxide is white, but at higher temperatures becomes yellow, returning to white as it cools.
Sometimes a humidity indicator is included in the desiccant to show, by color changes, the degree of water-saturation of the desiccant. One commonly used indicator is cobalt chloride (CoCl 2), which is blue when anhydrous, but turns purple upon bonding with two water molecules (CoCl 2 ·2 H 2 O).
The color of the flames also generally depends on temperature and oxygen fed; see flame colors. [5] The procedure uses different solvents and flames to view the test flame through a cobalt blue glass or didymium glass to filter the interfering light of contaminants such as sodium. [12] Flame tests are subject of a number of limitations.
Eventually, a less costly pigment was developed from cobalt ores, giving the color its present-day name. Cosmic Cobalt has been a favorite color for artists of every era. Getty Images/Wikimedia ...
Common indicators are cobalt(II) chloride and methyl violet. Cobalt (II) chloride is deep blue when dry and pink when wet, but it is toxic and carcinogenic, and was reclassified by the European Union in July 2000 as a toxic material. [29] Methyl violet may be formulated to change