The zinc It is a transition metal that belongs to group 12 of the periodic table and is represented by the chemical symbol Zn. It is the element number 24 in abundance in the earth's crust, found in sulfur minerals, such as sphalerite, or carbonates, such as smitsonite..
It is a metal highly known in popular culture; Zinc roofs are an example, as are supplements to regulate male hormones. It is found in many foods and is an essential element for countless metabolic processes. There are several benefits of its moderate intake compared to the negative effects of its excess in the body.
Zinc has been known long before its silver color galvanized steels and other metals. Brass, an alloy of varied composition of copper and zinc, has been a part of historical objects for thousands of years. Today its golden color is usually seen in some musical instruments.
Likewise, it is a metal with which alkaline batteries are made, since its reducing power and ease of donating electrons makes it a good option as an anodic material. Its main use is to galvanize steels, coating them with a layer of zinc that oxidizes or sacrifices to prevent the iron underneath from corroding later..
In its derivative compounds, it almost always has an oxidation number or state of +2. Therefore, the Zn ion is consideredtwo+ shrouded in molecular or ionic environments. While Zntwo+ it is a Lewis acid that can cause problems within cells, coordinated with other molecules, interacts positively with enzymes and DNA.
Thus, zinc is an important cofactor for many metallo-enzymes. Despite its enormously important biochemistry, and the brilliance of its greenish flashes and flames when burning, within the world of science it is considered a "boring" metal; since, its properties lack the attractiveness of other metals, as well as its melting point is considerably lower than theirs.
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Zinc has been manipulated for thousands of years; but in an unnoticed way, since ancient civilizations, including the Persians, Romans, Transylvanians and Greeks, already made brass objects, coins and weapons.
Therefore, brass is one of the oldest known alloys. They prepared it from the mineral calamine, Zn4YestwoOR7(OH)twoHtwoOr, which they ground and heated in the presence of wool and copper.
During the process, the small amounts of metallic zinc that could have formed escaped as vapor, a fact that delayed its identification as a chemical element for years. As the centuries passed, the brass and other alloys increased their zinc content, looking more grayish..
In the 14th century, in India, they had already managed to produce metallic zinc, which they called Jasada and they marketed it at that time with China.
And so the alchemists were able to acquire it to carry out their experiments. It was the renowned historical figure Paracelsus who named it 'zincum', possibly from the resemblance between zinc crystals and teeth. Little by little, in the midst of other names and various cultures, the name 'zinc' ended up curdling for this metal.
Although India already produced metallic zinc since the 1300s, this came from the method that used calamine with wool; therefore, it was not a metallic sample of considerable purity. William Champion improved on this method in 1738, Great Britain, using a vertical retort furnace.
In 1746 the German chemist Andreas Sigismund Marggraf obtained for the "first time" a sample of pure zinc by heating calamine in the presence of charcoal (a better reducing agent than wool), inside a container with copper. This way of producing zinc developed commercially and in parallel with Champion's.
Later, processes were developed that finally became independent of calamine, using zinc oxide instead; that is to say, very similar to the current pyrometallurgical process. The kilns also improved, being able to produce increasing amounts of zinc..
Until then, there was still no application that demanded huge amounts of zinc; but that changed with the contributions of Luigi Galvani and Alessandro Volta, who gave way to the concept of galvanization. Volta also came up with what is known as a galvanic cell, and zinc was soon part of the design of dry cells..
It is a grayish metal, usually available in granular or powder form. Physically it is weak, so it is not a good option for applications where it must support heavy objects.
Likewise, it is brittle, although when heated above 100 ºC it becomes malleable and ductile; up to 250 ºC, at which temperature it becomes brittle and sprayable again.
65.38 g / mol
30
419.53 ° C. This low melting point is indicative of its weak metallic bond. When melted it has an appearance similar to liquid aluminum.
907 ºC
460 ºC
-7.14 g / mL at room temperature
-6.57 g / mL at the melting point, that is, just when melting or melting
7.32 kJ / mol
115 kJ / mol
25,470 J / (mol K)
1.65 on the Pauling scale
-First: 906.4 kJ / mol (Zn+ gaseous)
-Second: 1733.3 kJ / mol (Zntwo+ gaseous)
-Third: 3833 kJ / mol (Zn3+ gaseous)
Empirical 134 pm
122 ± 4 pm
2.5. This value is considerably lower compared to the hardness of other transition metals, that is, tungsten..
Diamagnetic
116 W / (m K)
59 nΩm at 20 ° C
It is insoluble in water as long as its oxide layer protects it. Once this is removed by the attack of an acid or a base, the zinc ends up reacting with the water to form the complex aqueous, Zn (OHtwo)6two+, locating the Zntwo+ in the center of an octahedron bounded by water molecules.
When it burns, it can release toxic ZnO particles into the air. In the process, a greenish flame and glowing light are observed.
Zinc is a reactive metal. At room temperature it can not only be covered by an oxide layer, but also by basic carbonate, Zn5(OH)6(CO3)two, or even sulfur, ZnS. When this layer of varied composition is destroyed by the attack of an acid, the metal reacts:
Zn (s) + HtwoSW4(ac) → Zntwo+(ac) + SO42−(ac) + Htwo(g)
Chemical equation corresponding to its reaction with sulfuric acid and:
Zn (s) + 4 HNO3(ac) → Zn (NO3)two(ac) + 2 NOtwo(g) + 2 HtwoO (l)
With hydrochloric acid. In both cases, although not written, the complex aqueous Zn (OHtwo)6two+; except if the medium is basic, since it precipitates as zinc hydroxide, Zn (OH)two:
Zntwo+(aq) + 2OH-(ac) → Zn (OH)two(s)
Which is a white, amorphous and amphoteric hydroxide, capable of continuing to react with more OH ions-:
Zn (OH)two(s) + 2OH-(ac) → Zn (OH)4two-(ac)
Zn (OH)4two- is the zincate anion. In fact, when zinc reacts with such a strong base, such as concentrated NaOH, the complex sodium zincate, Natwo[Zn (OH4]:
Zn (s) + 2NaOH (aq) + 2HtwoO (l) → Natwo[Zn (OH4)] (aq) + Htwo(g)
Likewise, zinc can react with non-metallic elements, such as halogens in the gaseous state or sulfur:
Zn (s) + Itwo(g) → ZnItwo(s)
Zn (s) + S (s) → ZnS (s) (top image)
Zinc exists in nature as five isotopes: 64Zn (49.2%), 66Zn (27.7%), 68Zn (18.5%), 67Zn (4%) and 70Zn (0.62%). The others are synthetic and radioactive.
Zinc atoms crystallize into a compact but distorted hexagonal structure (hcp), a product of their metallic bond. The valence electrons that govern such interactions are, according to the electronic configuration, those belonging to the 3d and 4s orbitals:
[Ar] 3d10 4stwo
Both orbitals are completely filled with electrons, so their overlap is not very effective, even when the zinc nuclei exert an attractive force on them..
Consequently, the Zn atoms are not very cohesive, a fact reflected in their low melting point (419.53 ºC) compared to other transition metals. In fact, this is a characteristic of group 12 metals (along with mercury and cadmium), so they sometimes question whether they should really be considered elements of block d.
Although the 3d and 4s orbitals are full, zinc is a good conductor of electricity; therefore, its valence electrons can “jump” to the conduction band.
It is impossible for zinc to lose its twelve valence electrons or have an oxidation number or state of +12, assuming the existence of the Zn cation.12+. Instead, it loses only two of its electrons; specifically those of the 4s orbital, behaving similarly to alkaline earth metals (Mr. Becambara).
When this happens, zinc is said to participate in the compound with an oxidation number or state of +2; that is, assuming the existence of the Zn cationtwo+. For example, in its oxide, ZnO, zinc has this oxidation number (Zntwo+ORtwo-). The same applies to many other compounds, coming to think that only Zn (II) exists.
However, there is also Zn (I) or Zn+, which has lost only one of the electrons from the 4s orbital. Another possible oxidation number for zinc is 0 (Zn0), where its neutral atoms interact with gaseous or organic molecules. Therefore, it can be presented as Zntwo+, Zn+ or Zn0.
Zinc is in the 24th position of the most abundant elements in the earth's crust. It is generally found in sulfur minerals, distributed throughout the planet.
To obtain the metal in its pure form, it is first necessary to collect the rocks located in underground tunnels and concentrate the minerals rich in zinc, which represent the true raw material..
These minerals include: sphalerite or wurzite (ZnS), zincite (ZnO), willemite (ZntwoYes4), smitsonite (ZnCO3) and gahnite (ZnAltwoOR4). Sphalerite is by far the main source of zinc.
Once the mineral has been concentrated after a process of flotation and purification of the rocks, it must be calcined to transform the sulphides into their respective ones. In this step, the mineral is simply heated in the presence of oxygen, developing the following chemical reaction:
2 ZnS (s) + 3 Otwo(g) → 2 ZnO (s) + 2 SOtwo(g)
The SOtwo also reacts with oxygen to generate SO3, compound intended for the synthesis of sulfuric acid.
Once the ZnO has been obtained, it can undergo either a pyrometallurgical process, or electrolysis, where the end result is the formation of metallic zinc..
ZnO is reduced using coal (mineral or coke) or carbon monoxide:
2 ZnO (s) + C (s) → 2 Zn (g) + COtwo(g)
ZnO (s) + CO (g) → Zn (g) + COtwo(g)
The difficulty faced by this process is the generation of gaseous zinc, due to its low boiling point, which is overcome by the high temperatures of the furnace. That is why zinc vapors must be distilled and separated from the other gases, while their crystals condense on molten lead..
Of the two collection methods, this is the most widely used worldwide. ZnO reacts with dilute sulfuric acid to leach out zinc ions as its sulfate salt:
ZnO (s) + HtwoSW4(ac) → ZnSO4(ac) + HtwoO (l)
Finally this solution is electrolyzed to generate metallic zinc:
2 ZnSO4(ac) + 2 HtwoO (l) → 2 Zn (s) + 2 HtwoSW4(ac) + Otwo(g)
In the subsection on chemical reactions it was mentioned that hydrogen gas is one of the main products when zinc reacts with water. That is why, in the metallic state, it must be properly stored and out of the reach of acids, bases, water, sulfur or any source of heat; otherwise, there is a risk of fire.
The finer the zinc is divided, the greater the risk of fire or even explosion..
Otherwise, as long as the temperature is not close to 500 ºC, its solid or granular form does not represent any danger. If it is covered by a layer of oxide, it can be handled with bare hands, since it does not react with their humidity; however, like any solid, it is irritating to the eyes and respiratory tract.
Although zinc is essential for health, an excess dose can cause the following symptoms or side effects:
- Nausea, vomiting, indigestion, headaches and stomach aches or diarrhea.
- Displaces copper and iron during absorption from the gut, which is reflected in increasing limb weakness.
- Kidney stones.
- Loss of sense of smell.
Perhaps zinc is one of the metals, along with copper, that forms the most popular alloys: brass and galvanized iron. Brass has been observed on numerous occasions during a musical orchestra, as the golden glow of the instruments is due in part to the said alloy of copper and zinc..
Metallic zinc itself does not have many uses, although rolled up it serves as the anode for dry cells, and in powder form it is intended as a reducing agent. When a layer of this metal is electrodeposited on another, the former protects the latter from corrosion by being more susceptible to oxidation; that is, zinc oxidizes before iron.
That is why steels are galvanized (coated with zinc) to increase their durability. Examples of these galvanized steels are also present in endless “zinc” roofs, some of which come with a coat of green paint, and in bus bodies, household utensils and suspension bridges..
There is also aluzinc, an aluminum-zinc alloy used in civil constructions..
Zinc is a good reducing agent, so it loses its electrons for another species to gain; especially a metal cation. When in powder form, its reducing action is even faster than that of solid granules..
It is used in the processes of obtaining metals from their minerals; such as rhodium, silver, cadmium, gold and copper.
Likewise, its reducing action is used to reduce organic species, which may be involved in the oil industry, such as benzene and gasoline, or in the pharmaceutical industry. On the other hand, zinc dust also finds application in alkaline zinc-manganese dioxide batteries..
Zinc dust, given its reactivity and more energetic combustion, finds use as an additive in match heads, in explosives and fireworks (they impart white flashes and greenish flames)..
Zinc sulfide has the property of being phosphorescent and luminescent, which is why it is used in the production of luminous paints..
The white color of its oxide, as well as its semi and photo conductivity, is used as a pigment in ceramics and papers. In addition, it is present in talc, cosmetics, rubbers, plastics, fabrics, medicines, inks and enamels..
Our body needs zinc to fulfill many of its vital functions. To acquire it, it is incorporated in some nutritional supplements in the form of oxide, gluconate or acetate. It is also present in creams to relieve burns and skin irritations, and in shampoos.
Some benefits known or associated with taking zinc are:
- Improves the immune system.
- It is a good anti-inflammatory.
- Reduces the annoying symptoms of the common cold.
- Prevents cell damage in the retina, so it is recommended for vision.
- It helps regulate testosterone levels and is also associated with men's fertility, the quality of their sperm, and the development of muscle tissue..
- Regulates the interactions between brain neurons, which is why it is linked to improvements in memory and learning.
-And in addition, it is effective in the treatment of diarrhea.
These zinc supplements are commercially available as capsules, tablets, or syrups..
Zinc is thought to be part of 10% of the total enzymes in the human body, approximately 300 enzymes. Among them, carbonic anhydrase and carboxypeptidase can be mentioned..
Carbonic anhydrase, a zinc-dependent enzyme, acts at the tissue level by catalyzing the reaction of carbon dioxide with water to form bicarbonate. When the bicarbonate reaches the lungs, the enzyme reverses the reaction and carbon dioxide is formed, which is expelled to the outside during expiration.
Carboxypeptidase is an exopeptidase that digests proteins, releasing amino acids. Zinc works by supplying a positive charge that facilitates the interaction of the enzyme with the protein it is digesting..
Zinc is present in different organs of the human body, but it has the highest concentration in the prostate and in semen. Zinc is responsible for the proper functioning of the prostate and the development of the male reproductive organs.
Zinc is involved in the metabolism of RNA and DNA. Zinc fingers (Zn-fingers) consist of zinc atoms that serve as binding bridges between proteins, which together are involved in various functions.
Zinc fingers are useful in reading, writing, and transcription of DNA. In addition, there are hormones that use them in functions associated with growth homeostasis throughout the body..
Glutamate is the main excitatory neurotransmitter in the cerebral cortex and brainstem. Zinc accumulates in glutaminergic presynaptic vesicles, intervening in the regulation of the release of the neurotransmitter glutamate and in neuronal excitability.
There is evidence that an exaggerated release of the neurotransmitter glutamate may have a neurotoxic action. Therefore, there are mechanisms that regulate its release. Zinc homeostasis thus plays an important role in the functional regulation of the nervous system..
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