Aluminium Phosphate Formula, Physical & Chemical Behaviour
Aluminium Phosphate, or Aluminium (III) Phosphate, is an inorganic salt that is found in several minerals and is often used as a catalyst. It is also used in the pharmaceutical industry for manufacturing chemotherapeutic drugs. It occurs naturally in the form of the mineral berlinite. It is prepared chemically when soluble Aluminium salts are exposed to alkaline conditions. It is represented as AlPO4, which consists of hydrated Aluminium Orthophosphate. The Aluminium Phosphate solutions form polymeric aggregates wherein equilibrium is reached very slowly. It forms soluble Aluminium salts and Phosphoric acid by slowly reacting with Gastric acid.
However, it absorbs the bile acids weaker than Aluminium Hydroxide. Here, we will learn what is Aluminium Phosphate, what is the formula for Aluminium Phosphate, what is Aluminium Phosphate used for, and the properties of Aluminium Phosphate.
Aluminium Phosphate Structure- AlPO4
Aluminium Phosphate generally occurs as an anhydrous salt. However, its dihydrate and pentahydrate structures occur as well, which are represented as AlPO4.2H2O and AlPO4.5H2O.
The Aluminium Phosphate compound is formed by the Phosphate anion and Aluminium cation. Its anhydrous salt structure is much similar to several other minerals like quartz and has a trigonal crystal structure. However, its dihydrate form has a structure similar to NaCl in which 6 cations are coordinated to 6 anions. The structure of Aluminium Phosphate AlPO4 is shown below. This representation is commonly used for organic molecules.
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Chemical Formula of Aluminium Phosphate
Let us take a look at what is the chemical formula for aluminium phosphate.
Aluminium Phosphate is also called Aluminium Monophosphate or Mono-Aluminium Phosphate. It is formed by the Phosphate anion PO43-, and the Aluminium cation Al3+. Hence, the chemical or molecular formula of Aluminium Phosphate is AlPO4.
It occurs as a white crystalline powder. However, it is a colourless liquid in its aqueous form. It is insoluble in water and occurs in the form of a mineral berlinite. Aluminium phosphate is found in minerals like variscite and meta-variscite in its dihydrate form. Since it has piezoelectric properties, it is widely used in the electronic and electrical industries.
Now that you know about what is Aluminum Phosphate and what is the chemical formula for Aluminum Phosphate, let us take a look at some of its properties.
Physical Properties of Aluminium Phosphate AlPO4
Let us now discuss the physical properties of Aluminium Phosphate AlPO4 .
Chemical Properties of Aluminium Phosphate AlPO4
Now let us go through the chemical properties of Aluminium Phosphate AlPO4.
Aluminium Phosphate reacts with Hydrochloric Acid to form Aluminium Trichloride and Phosphoric acid. The reaction is as follows.
AlPO4 + 3HCl → AlCL3 + H3PO4
Aluminium Phosphate reacts with Magnesium Chloride to form Magnesium Phosphate and Aluminium Trichloride. The reaction is given as follows.
2AlPO4 + 3MgCl2 → Mg3(Po4)2 + 2AlCl3
FAQs on Aluminium Phosphate: Structure, Properties, and Applications
1. What is the chemical formula for Aluminium Phosphate?
The chemical formula for Aluminium Phosphate is AlPO₄. This compound is formed from the combination of the aluminium cation (Al³⁺) and the phosphate anion (PO₄³⁻). The equal and opposite charges of the ions balance each other out, resulting in a neutral ionic compound.
2. What are the most common real-world uses of Aluminium Phosphate?
Aluminium Phosphate has a wide range of applications across different industries due to its unique properties. Some of the most important uses include:
- Pharmaceuticals: It is used as an antacid to neutralise excess stomach acid and as an adjuvant in vaccines to enhance the body's immune response.
- Industrial Manufacturing: It serves as a base component in the production of ceramics, cements (including dental cement), and corrosion-inhibiting paints and coatings.
- Gels and Binders: Aluminium Phosphate gel is used as a binder in various applications, taking advantage of its ability to form stable suspensions.
- Cosmetics: It can be found in some cosmetic products as a white colourant or pigment.
3. How does Aluminium Phosphate work as an antacid?
Aluminium Phosphate functions as an antacid by acting as a weak base. When it enters the stomach, it reacts with and neutralises the excess hydrochloric acid (HCl), which is the primary cause of acidity and heartburn. This neutralisation reaction produces aluminium chloride and water, thereby increasing the pH of the stomach and providing relief from discomfort. Its low solubility ensures the effect is gradual and sustained.
4. What is the fundamental difference between Aluminium Phosphate (AlPO₄) and Aluminium Phosphide (AlP)?
It is crucial not to confuse Aluminium Phosphate with Aluminium Phosphide, as their properties and safety are vastly different. The key difference lies in the anion they contain:
- Aluminium Phosphate (AlPO₄) contains the polyatomic phosphate ion (PO₄³⁻). It is a relatively stable compound used in medicine and industry.
- Aluminium Phosphide (AlP) contains the monoatomic phosphide ion (P³⁻). This compound is extremely hazardous. It reacts rapidly with water or moisture in the air to release phosphine gas (PH₃), which is highly toxic and potentially lethal upon inhalation.
In summary, AlPO₄ is a stable salt, while AlP is a dangerous fumigant precursor.
5. Is Aluminium Phosphate considered safe for human use?
Yes, in the controlled amounts used in specific applications, Aluminium Phosphate is considered safe. For instance, when used as an antacid, its purpose is to neutralise stomach acid with minimal absorption into the body. As a vaccine adjuvant, it has a long history of safe use to help stimulate a stronger immune response. Similarly, related compounds like Sodium Aluminium Phosphate are recognised as safe (GRAS) for use as food additives by regulatory bodies like the FDA. However, its safety is context-dependent and relies on proper formulation and dosage, and it is entirely different from the highly toxic Aluminium Phosphide.
6. How is Aluminium Phosphate typically prepared in a laboratory setting?
A common method for preparing Aluminium Phosphate is through a precipitation reaction. This involves mixing aqueous solutions of a soluble aluminium salt, like aluminium sulfate (Al₂(SO₄)₃) or aluminium chloride (AlCl₃), with a soluble phosphate salt, such as sodium phosphate (Na₃PO₄). The Aluminium Phosphate, being largely insoluble in water, precipitates out as a solid, which can then be filtered, washed, and dried. The balanced chemical equation for the reaction with aluminium sulfate is: Al₂(SO₄)₃ (aq) + 2Na₃PO₄ (aq) → 2AlPO₄ (s) ↓ + 3Na₂SO₄ (aq).
7. What is the expected Van't Hoff factor (i) for Aluminium Phosphate?
This is a common conceptual trap for students. Theoretically, if Aluminium Phosphate (AlPO₄) were to fully dissociate in water, it would form two ions: Al³⁺ and PO₄³⁻, suggesting a Van't Hoff factor (i) of 2. However, AlPO₄ is a weak electrolyte and is only sparingly soluble in water. Due to its very low solubility, it exists almost entirely as an undissociated solid in equilibrium with the solution. Therefore, its effective Van't Hoff factor in a saturated aqueous solution is much closer to 1, not 2.
8. What type of crystal structure does Aluminium Phosphate have?
Aluminium Phosphate is an ionic compound that forms a crystal lattice structure. Interestingly, it exhibits polymorphism, meaning it can exist in several different crystalline forms. Many of its structures are analogous to those of silicon dioxide (SiO₂). For example, the berlinite form of AlPO₄ has a crystal structure that is very similar to that of α-quartz. In this structure, Al and P atoms alternate in the positions occupied by Si atoms in quartz, each tetrahedrally coordinated to four oxygen atoms.
