2. Aluminium hydroxide, Al(OH)₃, is found in nature as
the mineral gibbsite and its three much rarer
polymorphs: bayerite, doyleite and nordstrandite.
Aluminium hydroxide exist in many forms, all based
on the common combination of one aluminium atom
and three hydroxide molecules into different crystalline
arrangements that determine the appearance and
properties of the compound.
Gibbsite is the most chemically stable form of
aluminium hydroxide
3. In nature, the element aluminum
combines with other elements to form
compounds. Aluminum hydroxide is a
compound which is closely related to
aluminum oxide and aluminum oxide
hydroxide, the primary difference
between the three being the loss of
water. All three compounds are found
in bauxite, the ore used for creating
pure aluminum. While pure aluminum
is a metal, aluminum hydroxide is a
crystal.
4. Bauxite, an aluminium ore, is the world's
main source of aluminium. It consists mostly
of the minerals gibbsite (Al(OH)3),
bauxite mostly present near the village of Les
Baux in Provence, southern France.
5. It’s a odorless white powder.
Formula: Al(OH)3
Molar mass: 78.0036 g/mol
Density: 2.42 g/cm³
Melting point: 300 °C
Soluble in: Acid, Sulfuric acid, Alkali,
Hydrochloric acid (In Water….0.0001g/100ml)
Aluminium hydroxide is amphoteric in nature,
i.e, it has both basic and acidic nature.
6. Decomposition Reaction
Al(OH)3 Al2O3 + H2O
When it is heated to redness, It decomposes
into water and aluminium oxide.
Reaction with Acids
Al(OH)3 + 3HCl AlCl3 + 3H2O
The hydroxide reacts with acids readily that is
hydrochloric acid forming the water and the
aliminium salts.
7. Hot solution of potash alum is added slowly to a hot solution
of sodium carbonate.
The aluminium hydroxide is precipitated and then washed
thoroughly with hot water until it is free of sulfate ions.
3NaCO3+2KAl(SO4)2+3H2O 3Na2SO4 + K2SO4 + 2 Al(OH)3 + 2CO2
8. Aluminium hydroxide used commercially is manufactured by
the Bayer process which involves dissolving bauxite in sodium
hydroxide at temperatures up to 270 °C (518 °F). The waste
solid, bauxite tailings, is removed and aluminium hydroxide is
precipitated from the remaining solution of sodium aluminate.
2Al+2NaOH+2H2O−>2NaAlO2+3H2
2H2O+NaAlO2(aq)−>Al(OH)3(s)+NaOH(aq
9. Aluminium hydroxide is used as an Antacid.
Aluminium hydroxide is preferred over other alternatives such as sodium
bicarbonate because Al(OH)3, being insoluble, does not increase the pH of
stomach above 7 and hence, does not trigger secretion of excess acid by the
stomach. It reacts with excess acid in the stomach, reducing the acidity of the
stomach content, which may relieve the symptoms of heartburn or dyspepsia.
Such products can cause constipation, because the aluminum ions inhibit the
contractions of smooth muscle cells in the gastrointestinal tract, slowing
peristalsis and lengthening the time needed for stool to pass through the colon.
Some such products (such as Maalox) are formulated to minimize such effects
through the inclusion of equal concentrations of magnesium hydroxide or
magnesium carbonate, which have counterbalancing laxative effects.
10. It acts as astringent and antiseptic because of aluminium ions
formed by its solution in the hydrochloric acid of the stomach,
so also used as protective in treating peptic ulcer.
Precipitated Aluminium hydroxide is included as an adjuvant
in some vaccines (e.g. anthrax vaccine). Since it absorbs
protein well, it also functions to stabilize vaccines by
preventing the proteins in the vaccine from precipitating or
sticking to the walls of the container during storage.
11. Brand names as antacids
Alu-Cap, Aludrox, Gaviscon or Pepsamar.
brands for aluminium hydroxide
adjuvant
Alhydrogel, made by Brenntag Biosector
