7 Important Compounds of Aluminum and their Preparations
The compounds of aluminum are mainly covalent. In ionic compounds, such as aluminum fluoride, it exits as a trivalent aluminum ion, A13+. The hydrated aluminum ion is found in many compound e.g. A12(SO4)3 . 18H2O, and in aqueous solution Hydrated aluminum ions are usually acidic in aqueous solution. This post as also explains the industrial applications and uses of the various compounds of aluminum
Compounds of Aluminum
1. Aluminum Oxide, A12O3
This compound is commonly known as alumina. It occurs naturally as bauxite, corundum and white sapphire. It also occurs as ruby amethyst, topaz blue sapphire and emerald, the characteristic colour of which are due to other metallic oxide present as impurities. It is prepared by heating aluminum hydroxide or other aluminum compounds.
2A1(OH)3(s)→ A12O3(s) + 3H2O(g)
Aluminum oxide is a white crystalline powder which is almost insoluble in water. It reacts readily with dilute acids and strong alkalis to form salts, i.e it is amphoteric. Its reactions with acids and alkalis depend on the oxide being prepared at the lowest temperature possible, otherwise it will exits in a form which is insoluble in both acids and alkalis.
Aluminum oxide is used as a source of aluminum and in making furnace linings, ceramics and synthetic gem stones. It is also used as an abrasive, for absorption in chromatography, and as a catalyst in the catalytic cracking of hydrocarbons. This compound is one of the most widely used compounds of aluminium in industrial production processes.
2. Aluminum Hydroxide:- One of the most important compound of aluminum is Aluminum hydroxide. it is an amphoteric compound. In excess alkali, it gives tetrahydroxoaluminate(III) ion, and in acids, it forms salts.
A1(OH)3(s) + NaOH(aq)→ NaA1(OH)4(aq)
2A1(OH)3(aq) + 3H2SO4(aq)
→ A12(SO4)3(aq) + 6H20(1)
Aluminum hydroxide is used in the dyeing industry. It is called a mordant as it helps the dye to stick to the cloth.
3. Aluminum Chloride, AlCl3 Aluminum chloride is prepared by heating aluminum foils in a stream of dry chlorine or hydrogen chloride. The ease with which the anhydrous salt hydrolyzes explains why hydrogen chloride fumes are evolved from it in damp air.
Note: Sodium chloride and calcium chloride are electrovalent compounds which dissolve in water to give ions. Aluminum chloride, however, is a covalent compound which reacts with water.
4. Aluminum Tetraoxosulphate(VI), A12(SO4)3
This is also one of the important compounds of aluminum that occurs naturally but can be manufactured by the action of hot concentrated tetraoxosulphae(VI) acid on aluminum oxide.
A12O3(s) + 3H2SO4(aq)→ A12(SO4)3(aq) + 3H2O(1)
It is a white crystalline solid which is moderately soluble in water. It forms double salt (alums) with other tetraoxosulphates(VI), and is used in the treatment of water and sewage, and in paper making.
5. Alums
Alums are double traoxosulphates(VI) which ionize in solution to yield a monovalent cation (usually Na+=, K+ or NH4+), a trivalent cation (usually Fe3+, A13+ or Cr3+) and tetraoxosulphate(VI) ions. Their general formula can be written as follows.
M21SO4M2III(SO4)3, 24H2O or M1MIII(SO4)2.12H2O
Where M1and MIII are the monovalent and trivalent cations respectively.
All alums can be made by mixing equimolar masses of the tetraoxosulphates(VI) concerned. The alums crystallize out, each cation being associated with six molecules of water of crystallization. All alums have similar octahedral crystalline shapes.
Aluminum Potassium Tetraoxosulphate(VI)-dodlecahydrate, KA1(SO4)2. 12H2O: Also known as potash alum, is one of the commonest alums known. It is obtained by mixing hot solutions containing equimolar masses of potassium and aluminium tetraoxosulphates(VI). When the mixture is cooled, colourless crystals of the alum separate out.
Potash alum is usually used as a mordant in dyeing, i.e. it combines with and fixes the dyestuff onto the fibre in cases where the fibre cannot by dyed directly. Potash alum is also commonly used as a coagulant in water purification for removing colloidal suspension particles.
6. Aluminum Trioxonitrate(V), A1(NO3)3:
Aluminum nitrate may be prepared in the laboratory by dissolving aluminum oxide or aluminum hydroxide in dilute trioxonitrate(V) acid. the salt crystallizes out as nonahydrate crystals, A1(NO3)39H2O.
A12O3(s) + 6HNO3(aq) → 2A1(NO3)3,+ 3H2O(1)
A1(OH)3(s) + 3HNO3(aq) → A1(NO3)3,(aq)+ 3H2O(1)
7. Aluminum Hydride, A1H3
This is a white covalent solid. It can be prepared by reacting excess aluminum chloride with lithium hydride.
6LiH + A12C16 → 2A1H3 + 6LiCl
With excess lithium hydride, lithium tetrahydriod aluminate(III) is obtained.
8LiH + A12C16 → 2LiAIH + 6LiCl
Lithium tetrahydridoaluminate(III), LiA1H4,
and sodium terahydridobroate(III), NaBH4, are strong reducing agents used in organic chemistry.
Let’s now take a deeper look into the chemistry of the various compounds formed by aluminum in its reactions
The Chemistry of Compounds Formed by Aluminum
Aluminum, also known as alum, is a silvery-white metallic element. It is a member of Row 2 (Group 13) of the Periodic Table.
It is never found free in nature but is found combined with other elements in such minerals as bauxite, beryl and cryolite. It forms an oxide film that resists many acids but dissolves in alkaline solutions.
Phosphate
The compound aluminum phosphate is an inorganic salt consisting of an aluminium cation and a phosphate anion. The neutral chemical formula for this compound is AlPO4. The compound can be found in the form of a rock, a mineral or an inorganic salt. The mineral alum is the main source of aluminium phosphate, and it is used in manufacturing of a wide range of products including glass, ceramics and aluminum alloys.
The atomic structure of aluminum phosphate is tetrahedral. The compound has a low melting point and a high boiling point, which makes it easy to melt. It is also soluble in acids, but it is insoluble in water. The compound is isoelectronic with silicon dioxide, making it a material of interest in the field of microelectronics. It is also an excellent candidate for use as a phosphorus precursor in the production of semiconductors and high-pressure metallurgy.
Its amphoteric nature allows it to participate in acid-base reactions with various reactants. For example, it can react with acidic compounds such as HCl or HNO3. In addition to its reactivity, aluminium phosphate is able to bind to and adsorb substances. This property is useful in applications such as ceramics and pharmaceutical formulations.
Aluminum phosphate is commonly used in the manufacture of vaccines. It can improve the efficacy of live attenuated viral vaccines by preventing competition between different virus strains. It is also used as a carrier in the preparation of monovalent and multivalent vaccines, as well as in the delivery of live attenuated vaccines by intradermal administration.
While phosphate is essential for the human body, too much can be toxic. Excessive exposure over a prolonged period of time can cause neurological damage, bone health problems and kidney disease. The best way to prevent these risks is by following the proper safety precautions when working with phosphate. It’s important to follow the advice of a medical professional when using any medication or supplements that contain phosphate. This will ensure that you are receiving the right amount of phosphate for your specific needs.
Nitride
Aluminum nitride, whose chemical formula is AlN, is one of the newest members of the technical ceramics family. Although it was discovered more than 100 years ago, the development of a commercially viable product has occurred only within the last 20 years. It is a solid with high thermal and electrical conductivity and low corrosion resistance.
Nitride compounds of other metals, such as silicon nitride (SiN), titanium nitride (TiN) and boron nitride (BiN), are well known. The nitrides of gallium and indium also have high thermal conductivity, but they lack the ductility of aluminum nitride.
Aluminum nitride is a solid with a hexagonal wurtzite structure, in which each aluminium atom has four neighbouring nitrogen atoms at the corners of a tetrahedron. The structure is similar to that of the hexagonal diamond (lonsdaleite), but differs in that all tetrahedra are oriented in the same direction. The structure is stable at high temperatures and is hard to etch, but can be softened by hydration to form an amorphous layer with good mechanical properties.
The production of aluminum nitride involves reacting molten aluminum with a nitrogen precursor at pressures up to about 0.2 MPa (absolute). It is possible to dope the nitride by adding a magnesium, calcium or strontium compound. The dopants reduce the passivation of the aluminum and give the nitride desirable properties such as low thermal expansion coefficient and high electrical conductivity.
In addition to its insulating and conducting properties, aluminum nitride has good oxidation and corrosion resistance, as well as excellent mechanical strength. It has a lower density than alumina and is lighter than beryllium oxide, which makes it suitable for applications in space-related equipment.
It is also used in electronic devices such as light emitting diodes (LEDs), power LEDs and thin film microelectronics. Its exceptional mechanical and electrical properties make it particularly well suited to laser diodes and other radiation-sensitive components. It is also an ideal material for acoustic transducers due to its piezoelectric properties. This makes it a useful replacement for lead zirconate, titanium dioxide and other traditional materials. In addition, it can be fabricated into large-area wafers for use in integrated circuits and microelectronics.
Hydride
Aluminum is known to form a number of compounds with hydrogen, the most common being hydride. These compounds are solid, liquid or gaseous nonconductors with weak Van der Waals intermolecular interactions. Hydrogen bonds with highly electropositive s-block metals to form covalent hydrides. These compounds have low melting and boiling points. These hydrides are not chemically stable and are likely to explode when they come into contact with water or air. They are also unstable to oxidative attack and decomposition, although not as much as oxides.
The reaction of aluminum chloride with hydrogen gas gives the compound aluminum hydride AlH3 or alane, which is a strong base. This is an important reducing (hydride addition) reagent for organic synthesis in solution at both laboratory and industrial scales. The compound reacts with a wide variety of organic functional groups, including carboxylic acids and esters. It can also reduce nitro groups and carbon-carbon multiple bonds.
This reaction is a useful alternative to hydride-forming reagents such as sodium dithiosulfate and tris(diketiminyl)methylsilane. It is also more selective than the use of aqueous HCl for reduction reactions involving carboxylic acids. However, it is not a good choice for the reduction of nitro-containing compounds or carbonyl compounds, which require strong bases.
The aqueous salt of aluminum hydride is known as alum and has major commercial applications. It is used as a mordant for printing cloth and as a coagulant in water purification systems. It is also used to reduce the acidity of drinking water and for removing iron from wastewater. It is also used as a substitute for phenol in certain dental products.
In addition to being a useful reducing reagent, aluminum hydride can form covalent compounds with many ligands. It can also form complexes with boron and phosphido-boron ions to form boranes, which have been useful in organic synthesis. It can also form an ionic compound with lithium to make lithium aluminum hydride, which is a powerful Lewis acid and a common reducing agent in organic chemistry. It can also hydrate to produce the alkaline earth compound, aluminum acetate.
Alumina
Aluminum is the third most abundant metal in Earth’s crust. It is never found free in nature, however, and most of the aluminum on Earth is combined with other elements. Aluminum oxide, or alumina, is the most common of these compounds and is used as a starting material for smelting aluminum and in a wide range of advanced ceramics. It also serves as a raw material for chemical processing. Alumina is obtained from bauxite, a naturally occurring ore containing variable amounts of hydrous aluminum oxides. Alumina can also be produced synthetically. Aluminum oxide is a white, crystalline substance and has the chemical formula Al2O3. Corundum and ruby are natural forms of alumina and can be made into gemstones under certain circumstances.
Alumina has good thermal conductivity, even at elevated temperatures and is non-reactive to acids. It can be shaped into shapes and has high hardness. It is resistant to corrosion and can withstand alkali attacks. It has a very large surface area with which it can absorb gases, which gives it an excellent barrier property and enables it to serve as a shielding material.
In addition, alumina is a good electrical insulator and can be metal coated for use in high temperature brazing applications. It is also used as an abrasive for grinding and polishing purposes. It is an effective material for producing optical components, such as windows and mirrors and can be molded into body armor for military use.
When exposed to oxygen, alumina reacts to form aluminum hydroxide (Al(OH)3) and a variety of salts called aluminates. The latter are widely used in the textile industry. Aluminum hydroxide is also known as alum and was used in ancient times to set dyes on fabrics. It is still used today to make soaps and other cosmetic products. It is also a good deodorant and antiperspirant. Aluminum chloride is also a useful product and reacts with hydrogen to form aluminum hydride (AlH3), which is an important reducing agent in organic chemistry.
Some of the most useful aluminum compounds are intermetallic alloys that contain both aluminum and other metals, such as iron or silicon. These have a fixed relationship between the atoms of the two metals, as well as a constant chemical composition and chemical formula.
