The zinc hydroxide (Z n (OH) 2) is regarded as a chemical of inorganic nature, consisting solely of three elements: zinc, hydrogen and oxygen. It can be found in a rare way in nature, in different solid crystalline forms of three minerals that are difficult to find, known as sweetite, ashoverite and wülfingite.
Each of these polymorphs has characteristics intrinsic to its nature, although they commonly come from the same limestone rock sources and are found in combination with other chemical species.
By Alchemist-hp (talk) (www.pse-mendelejew.de), from Wikimedia Commons
In the same way, one of the most important properties of this substance is its ability to act as an acid or base depending on the chemical reaction that takes place, that is, it is amphoteric.
However, zinc hydroxide has a certain level of toxicity, eye irritation if you have direct contact with it and represents an environmental risk, especially in aquatic spaces.
Chemical structure
In the case of the mineral called sweetite, it is formed in oxidized veins found in the bed of limestone rocks, along with other minerals such as fluorite, galena or cerussite, among others.
Sweetite is made up of tetragonal crystals, which have a pair of axes of identical length and an axis of different lengths, originating at 90 ° angles between all axes. This mineral has a crystalline habit with a dipyramidal structure and is part of the 4 / m spatial set.
On the other hand, ashoverite is considered a polymorph of wülfingite and sweetite, becoming translucent and luminescent.
Furthermore, ashoverite (which is found together with sweetite and other polymorphs in limestone rocks) has a tetragonal crystalline structure, the cells of which intersect at the angles.
The other form in which zinc oxide is found is wülfingite, whose structure is based on the orthorhombic crystalline system, of the dysphenoidal type, and is found in star-shaped assemblages or inlays.
Obtaining
Various processes can be used to produce zinc hydroxide, including the addition of sodium hydroxide in solution (in a controlled manner) to one of the many salts that zinc forms, also in solution.
Since sodium hydroxide and zinc salt are strong electrolytes, they completely dissociate in aqueous solutions, so that zinc hydroxide is formed according to the following reaction:
2OH - + Zn 2+ → Zn (OH) 2
The above equation describes the chemical reaction that occurs for the formation of zinc hydroxide, in a simple way.
Another way to obtain this compound is through an aqueous precipitation of zinc nitrate with the addition of sodium hydroxide in the presence of the enzyme known as lysozyme, which is found in a large number of secretions such as tears and saliva of the animals, among others, in addition to having antibacterial properties.
Although the use of lysozyme is not essential, different structures of zinc hydroxide are obtained when the proportions and the technique by which these reagents are combined are altered.
Other reactions
Knowing that Zn 2+ gives rise to ions that are hexahydrated (when it is found in high concentrations of this solvent) and tetrahydrated ions (when it is found in small concentrations of water), it can be argued that by donating a proton from the complex formed to the OH ion - a precipitate (white in color) is formed as follows:
Zn 2+ (OH 2) 4 (aq) + OH - (aq) → Zn 2+ (OH 2) 3 OH - (aq) + H 2 O (l)
In case of adding sodium hydroxide in excess, the dissolution of this zinc hydroxide precipitate will occur with the consequent formation of a solution of the ion known as zincate, which is colorless, according to the following equation:
Zn (OH) 2 + 2OH - → Zn (OH) 4 2-
The reason zinc hydroxide dissolves is because this ionic species is commonly surrounded by water ligands.
By adding an excess of sodium hydroxide to this formed solution, what happens is that the hydroxide ions will reduce the charge of the coordination compound to -2, in addition to making it soluble.
On the other hand, if ammonia (NH 3) is added in excess, an equilibrium is created that causes the production of hydroxide ions and generates a coordination compound with +2 charge and 4 bonds with the ammonia ligand species.
Properties
As with the hydroxides that are formed from other metals (for example: chromium, aluminum, beryllium, lead or tin hydroxide), zinc hydroxide, as well as the oxide formed by this same metal, has amphoteric properties.
Being considered amphoteric, this hydroxide has a tendency to dissolve easily in a dilute solution of a strong acidic substance (such as hydrochloric acid, HCl) or in a solution of a basic species (such as sodium hydroxide, NaOH).
In the same way, when it comes to conducting tests to check the presence of zinc ions in solution, the property of this metal is used that allows the formation of the zincate ion when sodium hydroxide is added in excess to a solution containing zinc hydroxide. zinc.
Furthermore, zinc hydroxide can produce an amine coordination compound (which is soluble in water) when dissolved in the presence of excess aqueous ammonia.
As for the risks that this compound represents when it comes into contact with it, they are: it causes serious irritation to the eyes and the skin, it shows considerable toxicity to aquatic organisms and it represents long-term risks to the environment.
Applications
Despite being found in rare minerals, zinc hydroxide has many applications, among which is the synthetic obtaining of laminar double hydroxides (HDL) in the form of zinc and aluminum films, through electrochemical processes.
Another application that is usually granted is in the absorption process in surgical materials or dressings.
In the same way, this hydroxide is used in order to find zinc salts by mixing a salt of interest with sodium hydroxide.
There are also other processes that involve the presence of zinc hydroxide as a reagent, such as the hydrolysis of salts by coordination compounds of this compound.
Likewise, in the investigation of the properties that the surface presents in the reactive adsorption process in hydrogen sulfide, the participation of this zinc compound is analyzed.
References
- Wikipedia. (sf). Zinc Hydroxide. Recovered from en.wikipedia.org
- Pauling, L. (2014). General chemistry. Obtained from books.google.co.ve
- PubChem. (sf). Zinc Hydroxide. Recovered from pubchem.ncbi.nlm.nih.gov
- Sigel, H. (1983). Metal Ions in Biological Systems: Volume 15: Zinc and its Role in Biology. Obtained from books.google.co.ve
- Zhang, XG (1996). Corrosion and Electrochemistry of Zinc. Recovered from books.google.co.ve