The Aluminium Acetate Formula is represented as Al(CH₃COO)₃, making it a salt formed when aluminium hydroxide reacts with acetic acid. This compound is also called Aluminium Ethanoate or Aluminium Triacetate. It appears in NCERT Chemistry for Class 11 and Class 12 under salt hydrolysis and coordination chemistry topics. JEE and NEET aspirants must understand its molecular formula, molar mass, and chemical behaviour. This article covers everything — from the formula and derivation to solved examples, common mistakes, and exam tips.
Key Aluminium Acetate Formulas at a Glance
Quick reference for the most important formulas and facts about Aluminium Acetate.
- Molecular Formula: Al(CH₃COO)₃ or Al(C₂H₃O₂)₃
- Condensed Formula: \( \text{Al}(\text{CH}_3\text{COO})_3 \)
- Molar Mass: \( M = 204.11 \text{ g/mol} \)
- Preparation: \( \text{Al(OH)}_3 + 3\text{CH}_3\text{COOH} \rightarrow \text{Al(CH}_3\text{COO)}_3 + 3\text{H}_2\text{O} \)
- Salt Type: Salt of weak acid (acetic acid) and weak base (aluminium hydroxide)
- Solubility: Slightly soluble in water; hydrolyses readily
- Common Name: Aluminium Triacetate / Aluminium Ethanoate
What is Aluminium Acetate Formula?
The Aluminium Acetate Formula gives the chemical composition of a white, water-soluble salt formed by the combination of aluminium and acetate ions. Its molecular formula is Al(CH₃COO)₃, sometimes written as Al(C₂H₃O₂)₃. The compound is systematically named Aluminium Ethanoate or Aluminium Triacetate.
In the NCERT Chemistry syllabus, this compound is relevant to Class 11 Chapter 4 (Chemical Bonding) and Class 12 Chapter 7 (The p-Block Elements) where aluminium compounds are discussed. It is also studied under salt hydrolysis in ionic equilibrium.
Aluminium acetate exists in three forms: basic aluminium monoacetate, basic aluminium diacetate, and neutral aluminium triacetate. The neutral form Al(CH₃COO)₃ is the most commonly referenced in textbooks. It has a molar mass of approximately 204.11 g/mol. The compound is widely used in medicine, textile dyeing, and as an astringent. Understanding its formula and structure is essential for CBSE board exams and competitive entrance tests.
Aluminium Acetate Formula — Expression and Variables
The molecular formula of Aluminium Acetate is written as:
\[ \text{Al(CH}_3\text{COO)}_3 \]
This can also be expressed in expanded form as:
\[ \text{Al}_2(\text{C}_2\text{H}_3\text{O}_2)_6 \text{ (for the dimer)} \]
The most commonly used and accepted formula in CBSE and NCERT textbooks is \( \text{Al(CH}_3\text{COO)}_3 \). Each acetate group \( \text{CH}_3\text{COO}^- \) carries a charge of −1, and aluminium carries a charge of +3, making the compound electrically neutral.
| Symbol / Group | Quantity / Name | Value / SI Unit |
|---|---|---|
| Al | Aluminium (central metal) | Atomic mass = 26.98 g/mol |
| CH₃COO⁻ | Acetate ion (ethanoate ion) | Molar mass = 59.04 g/mol each |
| 3 × CH₃COO⁻ | Three acetate groups | 3 × 59.04 = 177.12 g/mol |
| M (Molar Mass) | Total molar mass of Al(CH₃COO)₃ | 204.11 g/mol |
| Oxidation State of Al | Charge on aluminium | +3 |
| Charge on CH₃COO⁻ | Charge on acetate | −1 each |
| Net Charge | Overall charge of compound | 0 (neutral salt) |
Derivation of Molar Mass
The molar mass of Aluminium Acetate is calculated by adding the atomic masses of all atoms in the formula Al(CH₃COO)₃.
The formula contains: 1 Al atom, 6 C atoms, 9 H atoms, and 6 O atoms.
\[ M = 1(26.98) + 6(12.01) + 9(1.008) + 6(16.00) \]
\[ M = 26.98 + 72.06 + 9.07 + 96.00 = 204.11 \text{ g/mol} \]
Each acetate group CH₃COO contributes C₂H₃O₂. Three such groups give C₆H₉O₆. Together with Al, the empirical formula becomes AlC₆H₉O₆, confirming the molar mass of 204.11 g/mol.
Preparation of Aluminium Acetate
Aluminium Acetate is prepared by reacting aluminium hydroxide with acetic acid. This is a classic acid-base neutralisation reaction. The balanced chemical equation is:
\[ \text{Al(OH)}_3 + 3\text{CH}_3\text{COOH} \rightarrow \text{Al(CH}_3\text{COO)}_3 + 3\text{H}_2\text{O} \]
In this reaction, aluminium hydroxide acts as the base. Acetic acid acts as the weak acid. Three moles of acetic acid react with one mole of aluminium hydroxide. Three moles of water are released as a byproduct.
Aluminium Acetate can also be prepared by reacting aluminium metal directly with acetic acid:
\[ 2\text{Al} + 6\text{CH}_3\text{COOH} \rightarrow 2\text{Al(CH}_3\text{COO)}_3 + 3\text{H}_2\uparrow \]
In this method, aluminium dissolves in excess acetic acid and hydrogen gas is released. Another preparation route involves reacting aluminium chloride with sodium acetate:
\[ \text{AlCl}_3 + 3\text{CH}_3\text{COONa} \rightarrow \text{Al(CH}_3\text{COO)}_3 + 3\text{NaCl} \]
This double displacement reaction gives aluminium acetate and sodium chloride as products. This method is commonly used in laboratory settings.
Physical and Chemical Properties of Aluminium Acetate
| Property | Value / Description |
|---|---|
| Appearance | White crystalline powder |
| Molar Mass | 204.11 g/mol |
| Density | Approximately 1.26 g/cm³ |
| Solubility in Water | Slightly soluble; hydrolyses in water |
| Odour | Faint acetic acid smell |
| pH of solution | Acidic (due to hydrolysis of Al³⁺) |
| Melting Point | Decomposes before melting |
| Nature | Salt of weak acid and weak base |
| Hydrolysis | Undergoes hydrolysis to give Al(OH)₃ and CH₃COOH |
Complete Chemistry Formula Sheet — Aluminium and Acetate Compounds
| Formula Name | Expression | Variables | Molar Mass | NCERT Chapter |
|---|---|---|---|---|
| Aluminium Acetate | \( \text{Al(CH}_3\text{COO)}_3 \) | Al = +3, CH₃COO⁻ = −1 | 204.11 g/mol | Class 12, Ch 7 |
| Aluminium Hydroxide | \( \text{Al(OH)}_3 \) | Al = +3, OH⁻ = −1 | 78.00 g/mol | Class 12, Ch 7 |
| Aluminium Chloride | \( \text{AlCl}_3 \) | Al = +3, Cl = −1 | 133.34 g/mol | Class 12, Ch 7 |
| Aluminium Oxide | \( \text{Al}_2\text{O}_3 \) | Al = +3, O = −2 | 101.96 g/mol | Class 12, Ch 7 |
| Aluminium Sulphate | \( \text{Al}_2(\text{SO}_4)_3 \) | Al = +3, SO₄²⁻ = −2 | 342.15 g/mol | Class 12, Ch 7 |
| Acetic Acid | \( \text{CH}_3\text{COOH} \) | C₂H₄O₂ | 60.05 g/mol | Class 12, Ch 12 |
| Sodium Acetate | \( \text{CH}_3\text{COONa} \) | Na = +1, CH₃COO⁻ = −1 | 82.03 g/mol | Class 12, Ch 7 |
| Ammonium Acetate | \( \text{CH}_3\text{COONH}_4 \) | NH₄⁺ = +1, CH₃COO⁻ = −1 | 77.08 g/mol | Class 12, Ch 7 |
| Basic Aluminium Acetate (Monoacetate) | \( \text{Al(OH)}_2(\text{CH}_3\text{COO}) \) | Al = +3, 2 OH⁻, 1 acetate | 136.08 g/mol | Class 12, Ch 7 |
| Basic Aluminium Diacetate | \( \text{Al(OH)(CH}_3\text{COO)}_2 \) | Al = +3, 1 OH⁻, 2 acetate | 178.12 g/mol | Class 12, Ch 7 |
Aluminium Acetate Formula — Solved Examples
Example 1 (Class 9-10 Level)
Problem: Calculate the molar mass of Aluminium Acetate, Al(CH₃COO)₃, given the atomic masses: Al = 27, C = 12, H = 1, O = 16.
Given: Formula = Al(CH₃COO)₃; Atomic masses: Al = 27, C = 12, H = 1, O = 16
Step 1: Count the atoms in Al(CH₃COO)₃.
Al = 1, C = 6 (2 per acetate × 3), H = 9 (3 per acetate × 3), O = 6 (2 per acetate × 3)
Step 2: Write the molar mass expression: \( M = 1(27) + 6(12) + 9(1) + 6(16) \)
Step 3: Calculate each term: \( M = 27 + 72 + 9 + 96 \)
Step 4: Add all values: \( M = 204 \text{ g/mol} \)
Answer
Molar Mass of Aluminium Acetate = 204 g/mol
Example 2 (Class 11-12 Level)
Problem: How many moles of acetic acid are required to completely react with 39 g of aluminium hydroxide to produce aluminium acetate? (Molar mass of Al(OH)₃ = 78 g/mol)
Given: Mass of Al(OH)₃ = 39 g; Molar mass of Al(OH)₃ = 78 g/mol; Reaction: Al(OH)₃ + 3CH₃COOH → Al(CH₃COO)₃ + 3H₂O
Step 1: Find moles of Al(OH)₃: \( n = \frac{\text{mass}}{\text{molar mass}} = \frac{39}{78} = 0.5 \text{ mol} \)
Step 2: Use the molar ratio. From the balanced equation, 1 mol Al(OH)₃ reacts with 3 mol CH₃COOH.
Step 3: Calculate moles of CH₃COOH required: \( n_{\text{CH}_3\text{COOH}} = 0.5 \times 3 = 1.5 \text{ mol} \)
Step 4: Calculate mass of acetic acid: \( m = 1.5 \times 60 = 90 \text{ g} \)
Answer
Moles of acetic acid required = 1.5 mol; Mass of acetic acid = 90 g
Example 3 (JEE/NEET Level)
Problem: Aluminium Acetate undergoes hydrolysis in water. Write the hydrolysis equation and predict whether the resulting solution is acidic, basic, or neutral. Justify your answer using Ka and Kb values (Ka of acetic acid = 1.8 × 10⁻⁵; Kb of Al(OH)₃ is very small, approximately 10⁻⁹).
Given: Salt = Al(CH₃COO)₃; Ka (CH₃COOH) = 1.8 × 10⁻⁵; Kb (Al(OH)₃) ≈ 10⁻⁹
Step 1: Identify the nature of the salt. Al(CH₃COO)₃ is a salt of weak acid (CH₃COOH) and weak base (Al(OH)₃).
Step 2: Write the hydrolysis equation: \[ \text{Al(CH}_3\text{COO)}_3 + 3\text{H}_2\text{O} \rightleftharpoons \text{Al(OH)}_3 + 3\text{CH}_3\text{COOH} \]
Step 3: Compare Ka and Kb. Ka = 1.8 × 10⁻⁵ is much larger than Kb ≈ 10⁻⁹.
Step 4: Since Ka > Kb, the acid (CH₃COOH) is stronger than the base (Al(OH)₃). The cation Al³⁺ hydrolyses more than the anion CH₃COO⁻. The solution is therefore acidic.
Step 5: Use the pH formula for salt of weak acid and weak base: \[ \text{pH} = 7 + \frac{1}{2}(\text{pKa} – \text{pKb}) \]
\[ \text{pKa} = -\log(1.8 \times 10^{-5}) \approx 4.74; \quad \text{pKb} = -\log(10^{-9}) = 9 \]
\[ \text{pH} = 7 + \frac{1}{2}(4.74 – 9) = 7 + \frac{1}{2}(-4.26) = 7 – 2.13 = 4.87 \]
Answer
The aqueous solution of Aluminium Acetate is acidic with an approximate pH of 4.87. This is because Ka of acetic acid is greater than Kb of aluminium hydroxide, meaning Al³⁺ hydrolyses more extensively than CH₃COO⁻.
CBSE Exam Tips 2025-26
- Memorise the formula correctly: Write Al(CH₃COO)₃, not Al(CH₃CO)₃. The acetate group is CH₃COO⁻, not CH₃CO⁻. This is a very common error in board exams.
- Know all three names: Aluminium Acetate, Aluminium Ethanoate, and Aluminium Triacetate all refer to the same compound. CBSE may use any of these names.
- Molar mass calculation: Always count atoms carefully — 1 Al, 6 C, 9 H, 6 O. We recommend practising this calculation at least twice before the exam.
- Preparation reactions: Learn all three preparation routes — from Al(OH)₃ + CH₃COOH, from Al + CH₃COOH, and from AlCl₃ + CH₃COONa. CBSE frequently asks for balanced equations.
- Salt hydrolysis: In the 2025-26 syllabus, ionic equilibrium questions often include salt of weak acid and weak base. Know that Al(CH₃COO)₃ gives an acidic solution because Ka > Kb.
- Uses in medicine: Aluminium acetate is used as an astringent and antiseptic. This factual detail appears in 1-mark questions in CBSE board exams.
Common Mistakes to Avoid
- Wrong formula writing: Many students write AlCH₃COO or Al(CH₃CO)₃ instead of the correct Al(CH₃COO)₃. Always include the full acetate group with both oxygen atoms.
- Incorrect atom count: Students often count only 4 C atoms instead of 6. Remember that each acetate group CH₃COO has 2 carbon atoms. Three groups give 6 carbons total.
- Confusing with Ammonium Acetate: Aluminium Acetate (Al(CH₃COO)₃) and Ammonium Acetate (CH₃COONH₄) are completely different compounds. Do not mix up their formulas or properties.
- Hydrolysis prediction error: Students often assume that salts of weak acid and weak base always give neutral solutions. This is wrong. The pH depends on the relative values of Ka and Kb. For Al(CH₃COO)₃, the solution is acidic, not neutral.
- Forgetting the charge balance: When writing the formula, always verify that the total positive charge equals the total negative charge. Al³⁺ + 3(CH₃COO⁻) = net charge of zero. This is a simple but important check.
JEE/NEET Application of Aluminium Acetate Formula
In our experience, JEE aspirants encounter the Aluminium Acetate Formula primarily in three contexts: salt hydrolysis, stoichiometry, and p-block chemistry. Understanding each context helps you score full marks on related questions.
1. Salt Hydrolysis and pH Calculation (JEE Main Pattern)
Al(CH₃COO)₃ is a classic example of a salt of weak acid and weak base. JEE Main frequently tests the formula for pH of such salts:
\[ \text{pH} = 7 + \frac{1}{2}(\text{pKa} – \text{pKb}) \]
You must know that Ka of acetic acid (1.8 × 10⁻⁵) is much larger than Kb of Al(OH)₃. This means the solution is acidic. JEE questions often ask you to identify whether the solution is acidic, basic, or neutral — and to justify your answer quantitatively.
2. Stoichiometry and Mole Concept (JEE Main and NEET)
Both JEE Main and NEET include mole concept problems involving aluminium salts. You may be asked to calculate the mass of Al(CH₃COO)₃ produced from a given mass of Al(OH)₃ or AlCl₃. The key steps are: find moles of reactant, apply molar ratio, and convert to mass using molar mass (204.11 g/mol).
3. p-Block Chemistry — Aluminium Compounds (JEE Advanced)
JEE Advanced tests deep knowledge of p-block elements. Aluminium forms many salts, and questions may compare the behaviour of AlCl₃, Al₂(SO₄)₃, and Al(CH₃COO)₃ in solution. Our experts suggest focusing on the amphoteric nature of Al(OH)₃ and how it reacts with both acids and bases to form different products. The reaction of Al(OH)₃ with acetic acid to give Al(CH₃COO)₃ is a standard example of this behaviour.
4. Medical Uses — NEET Biology-Chemistry Interface
NEET occasionally tests the application of inorganic compounds in medicine. Aluminium acetate is used as an astringent in ear drops and skin preparations. Knowing this application helps in NEET questions that link chemistry with pharmacology and biology.
Uses of Aluminium Acetate
| Field | Application | Form Used |
|---|---|---|
| Medicine | Used as an astringent and antiseptic in ear drops (Burow’s solution) | Basic aluminium acetate solution |
| Textile Industry | Used as a mordant in dyeing to fix dyes onto fabrics | Aluminium triacetate |
| Waterproofing | Used to make fabrics water-resistant | Basic aluminium acetate |
| Cosmetics | Used in antiperspirants and skin care products | Dilute solution |
| Paper Industry | Used as a sizing agent to improve paper quality | Aluminium acetate solution |
| Food Industry | Used as a food additive and preservative (limited use) | Dilute aluminium acetate |
FAQs on Aluminium Acetate Formula
For more chemistry formulas, visit our comprehensive Chemistry Formulas hub. You may also find these related articles helpful: Ammonia Formula, Bleaching Powder Formula, and Silicon Dioxide Formula. For official NCERT resources, visit ncert.nic.in.