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Aluminum hydroxide (Al(OH)3) is also called Aluminic acid or Aluminic hydroxide or Aluminium (III) hydroxide. In nature, it is found in the form of mineral gibbsite and its polymorphs such as doyleite, nordstrandite, and bayerite. Aluminium hydroxide is an amorphous powder white. It is insoluble in water but soluble in alkaline and acidic solutions. Let’s learn more about the chemical compound, aluminium hydroxide and discuss some important questions.
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Key Takeaways: Aluminium Hydroxide structure, properties, production, uses, health issues associated
Structure of Aluminium hydroxide
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Aluminium hydroxide has a structure of metal hydroxide which consists of hydrogen bonds. It comprises double layers of hydroxyl groups along with aluminium ions which occupy 2/3rd of the octahedral holes which form part of the middle of the two layers.
Chemical structure of Aluminium hydroxide
Gibbsite (raw material) is amphoteric and acts as a Brønsted-Lowry base in order to yield a salt by picking up the hydrogen ions and thereby neutralising the acid. The reaction is as follows:
3HCl + Al(OH)3 → AlCl3 + 3H2O
Furthermore, it acts as a Lewis acid in bases wherein it takes away the electron pair from the hydroxide ions. The reaction which occurs is as follows:
Al(OH)3 + OH– → Al(OH)4–
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Properties of Aluminium hydroxide
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Physical Properties: Aluminium hydroxide naturally occurs as odourless in nature. Furthermore, it is a white amorphous solid which has a density of 2.42gmL−1.
The melting point of aluminium is 300ºC. Furthermore, aluminium chloride is found to be insoluble in water as well as ethanol. However, it is found to be soluble in alkaline solutions as well as in acids.
Chemical Properties: Aluminium hydroxide is an amphoteric compound. This implies that aluminium hydroxide can demonstrate both acidic or basic characteristics depending on the reaction conditions.
Moreover, the substance is soluble in both acids and alkalis solutions. The following reaction demonstrates the same:
Al(OH)3 + 3H+→Al3+H2O
Al(OH)3 + OH−→AlO2−+H2O
Production of Aluminium Hydroxide
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Aluminium hydroxide is available in numerous geological systems in nature. However for commercial purposes, its production mostly takes place via the Bayer and sintering processes. These processes can result in obtaining alumina from the mineral bauxite.
Commercially used aluminium hydroxide is manufactured by the Bayer process. The process is carried out by dissolving bauxite in a sodium hydroxide solution at a temperature range up to 270°C. The waste produced in the process is removed and the sodium aluminate solution is allowed to precipitate. Therefore, the precipitate obtained is aluminium hydroxide. Alumina or aluminium oxide can be obtained from aluminium hydroxide by the process of calcination.
The steps involved in Bayer’s Process are as follows:
Step-1 : Al2O3.2H2O + 2 NaOH → 2 NaAlO2 + 3H2O
Step-2 : NaAlO2 + 2H2O → Al(OH)3 + NaOH
Step-3 : 2 Al(OH)3 → Al2O3 + 3H2O
There are various other processes which are used commercially in order to obtain aluminium hydroxide. They are micro-emulsion, the hydrothermal technique, and the Sol-gel method. A much higher level purity of the compound can be obtained from these methods in comparison to Bayer’s Process.
Uses of Aluminium Hydroxide
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Aluminium hydroxide has multiple different uses in the chemical industry. These uses of aluminium hydroxide include using the compound as rubber, plastic, epoxy resin filler, polymer, flame retardant, as well as an additive for glass/plastic.
In pharmaceuticals, aluminium hydroxide is effective as an antacid for the treatment of ulcer and gastritis.
Also, it can be used in some types of vaccines. Aluminium hydroxide works efficiently in the excipient production of some drugs. Aluminium hydroxide is used as a flame retardant in plastics.
The following is the list of uses for aluminium hydroxide:
- Used as an antacid.
- Used in aluminium Hydroxide gel.
- Used to manufacture activated alumina.
- Used as a filler in cosmetics.
- Used as a chemical intermediate.
- Used as a soft abrasive for plastics.
- Used in glass additive to increase resistance to thermal shock.
- Used in waterproofing fabrics.
- Used in the manufacturing of glass.
What are the health hazards associated with Aluminium hydroxide?
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Prolonged exposure to Aluminium(III) hydroxide causes irritation in eyes, respiratory system, and skin. When it comes in contact with water it causes a violent explosion.
Things to Remember
- Aluminium hydroxide acts as an antacid and is used to treat heartburn and sour stomach.
- It has the chemical formula (Al(OH)3).
- The base and acid are both the reactants of Aluminum Hydroxide.
- Aluminium Hydroxide is used to cover TiO2 nanoparticles.
- Aluminium Hydroxide is used medically to reduce phosphate levels in people with certain type of kidney conditions.
- The use of Aluminum Hydroxide results in reducing the absorption of other chemicals in the body. Thereby, spacing of two hours before and after taking Aluminum Hydroxide should be done in order to get the maximum benefits of taking medicines.
Sample Questions
Ques 1. What are the various uses of aluminium hydroxide? [2 marks]
Ans. Aluminium is a metal that occurs naturally. The antacid is the hydroxide of aluminium. Aluminium hydroxide is used in the treatment of heartburn, stomach pain, sore stomach or indigestion with acid. Aluminium hydroxide is also used in humans with other kidney disorders to reduce phosphate levels.
Ques 2. Is using aluminium hydroxide dangerous? [2 marks]
Ans. On prolonged exposure to the compound, it results in causing side effects which include intense stomach pain or constipation, loss of appetite; extreme discomfort while urinating; muscle weakness, excessive fatigue as well as extreme drowsiness.
Ques 3. Is aluminium hydroxide a weak base? [2 marks]
Ans. A weak base is a base that partially dissociates in solution, or breaks apart.
Aluminium hydroxide has molecular formula Al(OH)3 as a compound. Therefore, the hydroxide (OH) can act as a weak base when reacting with the strong acid, such as hydrochloric acid (HCl).
Ques 4. What is another name for aluminium hydroxide? [ 1 mark]
Ans. Aluminium hydroxide is available as an over-the-counter antacid drug which is used to treat peptic ulcer as well as hyperphosphatemia.
Ques 5. What is aluminium hydroxide gel? [3 marks]
Ans. Aluminium Hydroxide gel can be defined as the suspension of the amorphous Aluminum Hydroxide. The gel form of the mineral can be used to suspend material such as glycerin, peppermint oil, saccharin, sucrose and sorbitol along with various other flavours. The gel can also be used for medical purposes wherein it can be used to suspend different concentrations of drugs such as antimicrobials.
The gel is prepared via the process of precipitation of the ethanolic solutions of aluminium chloride. Primary amines such as octylamine, propylamine and dodecylamine are also added to enhance the process of gel formation. These amines serve as proton acceptors and thus makes the process of precipitation a possibility during hydrolysis.
Ques 6. How does Aluminium hydroxide react? [3 marks]
Ans. The formation of Aluminum Hydroxide includes the process of it slowly dissolving in the stomach and then reacting with the hydrochloric acid present which leads to the formation of aluminium chloride as well as water.
The process of formation of water and aluminium hydroxide also inhibits pepsin action by increasing pH and with the help of adsorption. Cryoprotective effects may occur because of the increased bicarbonate ions (HCO3-) and prostaglandin levels in the body.
In water, Aluminum Hydroxide behaves as an amphoteric substance, which means that iit acts as an acid before forming a solid and as a base before formation of solid acid.
Ques 7. Under what circumstances does aluminium hydroxide produce precipitate? [3 marks]
Ans. When aluminium salt is added to water around a neutral pH, Al hydroxide rain forms rapidly. Initially, the rain is in the form of key nano-scale particles, which then combine to form flocs. The nature of flocs depends largely on the composition of the solution, for example in the presence of humic acid (HA), which not only increases the size of the base nanoparticles but also reduces the contact points between them. Therefore, these are the circumstances in which Aluminum Hydroxides are formed with the help of water in presence of a neutral pH.
Ques 8. What results in the aluminium hydroxide to be an acid? [2 marks]
Ans. Aluminium hydroxide is insoluble in water and can be dissolved only in bases and acids. Aluminium hydroxide is expected to act as an inactive amphoteric material in water. However, Aluminium hydroxide will operate as an acid if a strong base is present in the reaction mixture.
Ques 9. What causes phosphate deficit in aluminium hydroxide? [2 marks]
Ans. Aluminium hydroxide may induce phosphorus deficiency in people with low phosphorus diets by interacting with phosphates in order to generate insoluble aluminium phosphate.
Ques 10. Is it safe to use aluminium hydroxide in cosmetics? [2 marks]
Ans. Hydroxide in aluminium is the artificial substance that functions as an opacifier. Agent and absorbent for painting are two of the most common applications. There is no evidence that aluminium hydroxide is in any way harmful to the skin in the present form in which it is used.
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