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Aluminium Hydroxide Formula – Structure, Properties, Uses, Sample Questions

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  • Last Updated : 23 May, 2022

Aluminic acid, Aluminic hydroxide, and aluminum (III) hydroxide are all names for aluminum hydroxide. It is the chemical term for aluminum, as are all other metal carbonates, sulfates, and hydroxides. 
It may be found in nature as the mineral gibbsite and its polymorphs, such as doyleite, nordstrandite, and bayerite.

Aluminum Hydroxide formula 

The chemical formula of aluminum hydroxide is Al(OH)3. Aluminic hydroxide is a white amorphous powder. It is water-insoluble but soluble in alkaline and acidic solutions. It can be used to treat stomach discomfort, acid indigestion, heartburn, and sour stomach. It can also be used to lower phosphate levels in persons who have renal difficulties. The antacid may also be useful for non-medical applications. 

Structure of Aluminum Hydroxide


Aluminum hydroxide is an amphoteric chemical with the ability to behave as both an acid and a base. It occurs in acidic solutions as the aluminum ion, Al3+, and the hydroxide ion, OH. It occurs in basic solutions such as the aluminum hydroxide ion, Al(OH)4-. The aluminum hydroxide ion has a tetrahedral structure with a bond angle of 116.5° between Al-O-Al. Aluminic hydroxide has the normal metal hydroxide structure with hydrogen bonding.
It is made up of two layers of hydroxyl groups and two layers of aluminum ions, which occupy two-thirds of the octahedral holes generated between the two layers.

Gibbsite is an amphoteric mineral that functions as a Bronsted-Lowry base to produce salt by absorbing hydrogen ions and neutralizing the acid. Here is the Reaction,

3HCl + Al(OH)3 → AlCl3 + 3H2O

In bases, it acts as a Lewis acid. It reduces the hydroxide ions of an electron pair. Another reaction is,

Al(OH)3 + OH→ Al(OH)4– 

Preparation of Aluminum Hydroxide 

The Bayer process is used to produce commercially used aluminum hydroxide. It is accomplished by dissolving bauxite in a sodium hydroxide solution at temperatures ranging from 0 to 270°C. After removing the trash, the sodium aluminate solution is allowed to precipitate. As a result, the precipitate formed is aluminum hydroxide.
Calcination can be used to produce alumina or aluminum oxide from aluminum hydroxide. 

Bayer Process Reactions

  • First: Al2O3.2H2O + 2 NaOH → 2 NaAlO2 + 3 H2O
  • Second: NaAlO2 + 2 H2O → Al(OH)3 + NaOH
  • Third: 2 Al(OH)3 → Al2O3 + 3 H2O

Physical Properties of Aluminum Hydroxide 

The following are the physical characteristics of aluminum hydroxide,

  1. Aluminum hydroxide occurs in the form of a white amorphous powder.
  2. Aluminum hydroxide has a melting point of around 573K.
  3. Aluminum hydroxide is insoluble in water but soluble in alkalis and acids.
  4. Solid aluminum hydroxide has a density of around 2.42g/cm3.

Chemical Properties of aluminum Hydroxide 

  1. Aluminum hydroxide is an amphoteric substance.
  2. It may function as both an acid and a base.
  3. Aluminum hydroxide behaves as a Bronsted–Lowry base in acids.
  4. As a result, it neutralizes the acid-forming salt and water that are the end results. 

Uses of Aluminum Hydroxide 

  • Aluminum hydroxide offers several benefits, including large-scale manufacturing, sufficient raw resources, excellent product purity, and good acid solubility. As a result, aluminum hydroxide may be employed as a key raw material in the production of aluminum salts such as barium aluminate, aluminum sulfate, and others.
  • Because of its filling, flame retardant, smoke-eliminating properties, and non-toxicity, aluminum hydroxide powder is widely recognized as a suitable flame retardant filler for plastics, unsaturated polyester, rubber, and other organic polymers. The flame retardant mechanism of aluminum hydroxide is as follows: when the temperature is above 200°C, the aluminum hydroxide begins to conduct endothermic breakdown and releases three crystal water, and its decomposition rate reaches its maximum at 250°C. 
  • Aluminum hydroxide may be converted into alumina, a material with good thermal chemical stability, thermal strength, creep resistance, dielectric characteristics, and a low thermal expansion coefficient. Alumina is a critical ingredient in the production of ceramics.
    We can regulate the phase development of the composite during the ceramic synthesis process by activating aluminum hydroxide and managing the crystallization process.
  • Aluminum hydroxide occurs in water mostly in the form of Al(OH)4, which may precipitate hazardous heavy metals in sewage using the coprecipitation technique to accomplish water purification after additional filtering.  Aluminum hydroxide has a large specific surface area and may adsorb colloid, suspended particles, colors, and organic compounds from sewage. 
  • Aluminum hydroxide has the ability to neutralize gastric acid and is non-toxic, which is why it is constantly employed as a traditional medication for stomach therapy.
    The use of aluminum hydroxide as an adjuvant can also boost the immunogenicity of the vaccine. The mechanism of action is as follows: aluminum hydroxide adsorbs antigen on its surface, allowing the antigen to be released slowly, hence extending effectiveness.
  • By controlling the temperature, concentration, and pH of the reactants, we can obtain a variety of target products with varying surface area, pore-volume, pore structure, and crystal structure, which can be effectively used as a catalyst carrier for the hydrogenation of unsaturated carbonyl compounds and the preparation of fullerenes and other similar compounds. 
  • Aluminum hydroxide has a high whiteness, ultrafine particle size, and full crystal shape, and it is very compatible with brighteners. Aluminum hydroxide, as an additional coating and resin, may significantly increase coated paper’s whiteness, opacity, smoothness, and ink absorption.

Sample Questions 

Question 1: What is the function of aluminum hydroxide?


Aluminum is a naturally occurring metal. aluminum hydroxide is the antacid. aluminum hydroxide is used to treat heartburn, stomach discomfort, aching stomach, and acid indigestion. aluminum hydroxide is also used to lower phosphate levels in persons with various renal diseases. 

Question 2: Explain the importance of Aluminum Hydroxide gel?


Aluminum Hydroxide gel is an amorphous Aluminum Hydroxide suspension. Partially carbon replacements are present in the mineral gel form. Glycerin, peppermint oil, saccharin, sucrose, and sorbitol, among other ingredients, may be present in the gel form. Different antibacterial components can also be present in appropriate concentrations in the gel. It is primarily used to treat symptoms caused by an excess of stomach acid, such as heartburn, acid indigestion, and stomach distress. It works better than pills or capsules. Precipitation of ethanolic solutions of aluminum chloride results in the formation of the gel and Primary amines, such as octylamine, propylamine, and dodecylamine, are also present.
These act as proton acceptors during hydrolysis, allowing precipitation to occur. 

Question 3: Is it safe to use aluminum hydroxide in cosmetics?


Hydroxide in aluminum 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 aluminum hydroxide is harmful to the skin. 

Question 4: Is aluminum hydroxide harmful?


Aluminum hydroxide side effects include severe stomach pain or constipation, a loss of appetite, difficulty when peeing, muscular weakness, weariness, and excessive sleepiness. 

Question 5: Is alkali hydroxide a weak base?


As a chemical compound, aluminum hydroxide has the molecular formula Al(OH)3…. In aluminum hydroxide, for example, the hydroxide (OH) can function as a weak base when interacting with the strong acid, hydrochloric acid (HCl). A weak base is one that partially dissociates or breaks away in solution. 

Question 6: What causes aluminum hydroxide to be an acid? 


Aluminum hydroxide is insoluble in water and can only be dissolved in bases and acids. Aluminum hydroxide is expected to serve as an amphoteric material in water. 

Aluminum hydroxide will operate as an acid if a strong base is present. 

Question 7: What causes phosphate deficit in aluminum hydroxide? 


Aluminum hydroxide may induce phosphorus deficit in people with low phosphorus diets by interacting with phosphates to generate insoluble aluminum phosphate. 

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