An introduction to Aluminum Hydroxide
Aluminium hydroxide is an inorganic compound made up of aluminium ion and hydroxide ions. It is an amphoteric compound which means it can act as an acid as well as a base. Aluminium hydroxide minerals occur in nature. It holds the property of an antacid. The IUPAC name of the aluminium hydroxide is Aluminium trioxide.
Hydrophobicity is a property of aluminium hydroxide. In most cases, it produces lyophobic solutions. The hydrolysis of aluminium chloride can be used to prepare aluminium hydroxide gels.
3H₂O + AlCl₃ Al(OH)₃ + 3HCl
Aluminium Compounds
Aluminium is an inorganic element belonging to the thirteenth group. Aluminium reacts with nitrogen gas and forms an aluminium nitride
Al + N₂ → AlN
Aluminium reacts with the oxygen gas and forms aluminium trioxide also known as alumina.
Al + O₂ → Al₂O₃
Aluminium reacts with hydrochloric acid and forms aluminium trichloride as a product and hydrogen gas as a byproduct. This aluminium trichloride is used in the preparation of aluminium hydroxide gels.
Al + HCl → AlCl₃ + H₂
Aluminium reacts with the dilute sodium hydroxide solution and forms aluminium trihydroxide. This molecule is amphoteric in nature. Therefore, it further reacts with the dilute sodium hydroxide solution and forms sodium meta illuminate aa a product and hydrogen gas as a byproduct.
Al + NaOH (dil) → Al(OH)₃ → Na[Al(OH)₄] + H₂
Aluminium hydroxide reacts with the water molecules and forms a solution. This reaction can be used to clear drains. This reaction is also used to remove the obstructions from the drainage pipe.
AlCl₃ + H₂O → [Al (H₂O)₆]⁺³ + 3Cl⁻
Aluminium trichloride reacts with hydrochloric acid and forms white fumes.
AlCl₃ + HCl → white fumes
Structure of Aluminium Hydroxide
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Aluminium cation is attracted with three hydroxide anions.
Properties of Aluminium Hydroxide
The Colour of aluminium hydroxide is white.
Its density is 2.43 g/cm³.
Its melting point is 300 degrees celsius.
Its molar mass is 78.0036.
Aluminium Hydroxide Gel Preparation
Aluminium hydroxide is hydrophobic in nature. Generally, it forms lyophobic solutions. Aluminium hydroxide gel preparation can be done with the hydrolysis of aluminium chloride.
AlCl₃ + 3H₂O → Al(OH)₃ + 3HCl
Step by Step Aluminium Hydroxide Gel Preparation
Prepare the 2% aluminium chloride solution (by adding 2g of aluminium chloride in 100 ml water).
Add 100 ml distilled water to the conical flask.
Boil the water with the help of the wire gauze.
Add 10 ml of the above prepared 2% aluminium chloride solution. Add this solution with the help of the dropper of the burette. As aluminium compounds are violent in nature.
Constantly stir the solution while adding aluminium chloride.
Heat the solution until you see a coloured solution. The colour of the aluminium hydroxide solution is white.
Leave the mixture for cooling at normal temperature.
The cooling solution is called aluminium hydroxide gel.
Precaution You Need to keep During Aluminium Hydroxide Gel Preparation
Clean the conical flask with a steaming process to avoid any kind of impurities.
The byproduct (Hydrochloric Acid) formed in this reaction causes destabilization of the prepared gel. therefore, needs to be removed by the dialysis process.
Aluminium chloride solutions need to be added in a dropwise manner.
Uses of Aluminium Hydroxide Gel
It is used for treating gastric ulcers.
It is used in making vaccines.
It is used in cosmetics.
It serves as an intermediate compound in various reactions.
It is used as a flame retardant.
It is used in the manufacturing of certain drugs.
Side Effects of Aluminium Hydroxide Gel
Aluminium hydroxide is generally used as a medicine. But to some people, it shows side effects when consumed. These side effects involve:
Constipation is a possibility. Other issues, such as haemorrhoids and intestinal blockage, could result as a result of this. Contact your doctor or pharmacist right away if constipation persists or worsens.
If your doctor has prescribed this drug, ensure that he or she has determined that the benefits are more and the side effects are negligible. The majority of people who use this medication experience no significant side effects.
Exercise daily and drink ample amounts of water to avoid constipation. Constipation can be avoided by taking this medicine with a magnesium-containing antacid. Stool softeners may be beneficial as well. Other antacids, stool softeners, and laxatives might be discussed with your doctor or pharmacist.
In the intestines, aluminium-containing antacids bind to phosphate, a vital physiological component. If your kidneys are normal, this can result in low phosphate levels, especially if you take big dosages for a long time.
Get medical help right away if you experience any of the following side effects or symptoms of a serious medical problem: black/tarry stools, mental/mood disorders (e.g., confusion, deep sleep), pain with urination, stomach/abdominal pain, or vomit that looks like coffee grounds.
This medicine seldom causes a severe allergic reaction. However, if you witness any symptoms of some allergic response, such as a rash, redness, itching/swelling (particularly of the face/tongue/throat), extreme dizziness, or shortness of breath, go to the doctor right away.
This is a very important list of some potential adverse effects. Contact your doctor or pharmacist if you have any other side effects not listed above.
Aluminium Hydroxide: How to Use It
Before each dose, give the bottle a good shake. The flavour of the suspension may be improved by refrigerating it. Do not allow yourself to become frozen. This drug is most effective when taken without any other liquids. If necessary, dilute your dose with a little water.
This contains aluminium, which can interfere with the absorption of other medications (such as digoxin, iron, tetracycline antibiotics, pazopanib, and quinolone antibiotics like ciprofloxacin). To avoid this problem, talk to your doctor or pharmacist about how to schedule your medications.
If your acid problems persist or worsen after one week of use, or if you suspect you have a significant medical concern, seek medical help right away.
Did You Know?
Aluminium hydroxide reacts with both acid and base.
Aluminium hydroxide is used in coating TiO2 nanoparticles.
Aluminium hydroxide is used to reduce phosphate levels in people with certain kidney conditions.
Aluminium hydroxide consumption reduces the absorption of the other medicines in the body. Therefore, two-hour gaps before and after taking aluminium hydroxide should be maintained for consuming other medicines with this.
Hence the article is very useful for the students to understand the properties, structure of aluminium hydroxide. Step by Step procedure of preparation of aluminium hydroxide gel is given in the above article.
FAQs on Aluminium Hydroxide Gel Preparation
1. What is aluminium hydroxide gel and what is its chemical formula?
Aluminium hydroxide gel is a colloidal suspension of aluminium hydroxide in water. It is an inorganic compound with the chemical formula Al(OH)₃. In its gel form, it acts as an amorphous, gelatinous precipitate that is widely used in pharmaceuticals, particularly as an antacid.
2. How is aluminium hydroxide gel prepared in a laboratory?
A common laboratory method for preparing aluminium hydroxide gel involves a double decomposition reaction. It is typically prepared by adding a solution of an alkali, like ammonium hydroxide (NH₄OH) or sodium hydroxide (NaOH), to a solution of an aluminium salt, such as aluminium chloride (AlCl₃). This causes the precipitation of a gelatinous white substance, which is the aluminium hydroxide gel. The precipitate is then purified through dialysis to remove excess ions.
3. What are the main uses of aluminium hydroxide gel in medicine?
The primary medical use of aluminium hydroxide gel is as an antacid. It helps to:
- Neutralise excess stomach acid (hydrochloric acid).
- Relieve symptoms of acid indigestion, heartburn, and upset stomach.
- Treat conditions like peptic ulcers and gastritis.
- Act as a phosphate binder in patients with kidney failure to reduce high phosphate levels in the blood.
4. Why is aluminium hydroxide gel an effective antacid?
Aluminium hydroxide gel is an effective antacid because of its amphoteric nature and slow-reacting properties. It neutralises the hydrochloric acid (HCl) in the stomach to form aluminium chloride and water, thereby increasing the stomach's pH. The reaction is Al(OH)₃ + 3HCl → AlCl₃ + 3H₂O. Its slow action provides sustained relief without causing a sudden "acid rebound," where the stomach overproduces acid in response to rapid neutralisation.
5. What is the difference between aluminium hydroxide gel and dried aluminium hydroxide gel?
The main difference lies in their physical state and water content. Aluminium hydroxide gel is an aqueous suspension of hydrated aluminium oxide. In contrast, dried aluminium hydroxide gel is the same substance after it has been dried to a powder form, containing a much lower percentage of water. The dried form is often used to manufacture tablets and capsules, while the wet gel is used for liquid oral suspensions.
6. Besides being an antacid, what are other applications of aluminium hydroxide?
Beyond its use as an antacid, aluminium hydroxide has several other important applications:
- Vaccine Adjuvant: It is used in some vaccines to enhance the body's immune response to the antigen.
- Flame Retardant: It is used as a fire-retardant filler for polymer applications.
- Water Purification: It acts as a flocculant to remove suspended particles from water.
- Cosmetics: It serves as an opacifying agent and skin protectant in products like foundations and lotions.
7. What chemical reaction is involved in the preparation of aluminium hydroxide gel from an aluminium salt?
The preparation typically involves a precipitation reaction. When a solution of aluminium chloride (AlCl₃) is treated with a base like ammonium hydroxide (NH₄OH), aluminium hydroxide precipitates out as a gel. The balanced chemical equation for this reaction is: AlCl₃(aq) + 3NH₄OH(aq) → Al(OH)₃(s)↓ + 3NH₄Cl(aq). The downward arrow (↓) indicates the formation of a solid precipitate.
8. How is the purity and strength of aluminium hydroxide gel tested (assay)?
The assay of aluminium hydroxide gel is performed to determine its acid-neutralising capacity. A known weight of the gel is dissolved in a specific volume of a standardised hydrochloric acid (HCl) solution in excess. The mixture is heated to ensure complete reaction. After cooling, the unreacted (excess) HCl is titrated against a standardised solution of sodium hydroxide (NaOH) using an indicator like methyl orange. The amount of HCl consumed by the gel is then calculated, which indicates its strength.
9. What are the common side effects or precautions when using aluminium hydroxide gel?
While generally safe, the most common side effect associated with aluminium hydroxide is constipation. This is why it is often formulated with magnesium hydroxide, which has a laxative effect. Other potential side effects include loss of appetite and muscle weakness. It's also important to note that it can interfere with the absorption of other medications, so it should be taken at a different time from other drugs.
10. Why is aluminium hydroxide often combined with magnesium hydroxide in antacid formulations?
Aluminium hydroxide is combined with magnesium hydroxide in antacids for two key reasons. First, it balances out the side effects: aluminium hydroxide tends to cause constipation, while magnesium hydroxide can cause diarrhoea. Combining them results in a more neutral effect on bowel movements. Second, they have different reaction speeds. Magnesium hydroxide is a relatively fast-acting antacid, while aluminium hydroxide is slower but provides longer-lasting relief. Their combination offers both quick and sustained neutralisation of stomach acid.
