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Preparing aluminium hydroxide solution is one of the most important experiments. Aluminium hydroxide can be easily prepared in the lab by heating aluminium chloride in 100 ml of distilled water. White color solution of aluminium hydroxide will be observed. In order to produce aluminium hydroxide on a large scale, Bayer’s process can be used.
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Aim
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To prepare Aluminium hydroxide solution.
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Theory
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The nature of aluminium hydroxide is hydrophobic. The hydroxide can be obtained when aluminium chloride undergoes the process of hydrolysis. The reaction which takes place in the process is given below:
As you can see HCl is produced as the byproduct apart from the required aluminium hydroxide. This HCl is seen as the ionic impurity which has to be removed so that the main product is not affected. In order to remove the HCl, the process of dialysis takes place.
Properties of Aluminium Hydroxide
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Aluminium hydroxide having the chemical formula of Al(OH)3 is an amphoteric hydroxide. It has a molar mass of 78g/mol and the melting point is about 300 degrees celsius. When aluminium hydroxide reacts with an acid, it will act as a Bronsted Lowry base, therefore, will accept protons. It also has the property of acting as a Lewis acid when reacted with a base and so accepts an electron from a hydroxyl anion.
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Materials Required
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- Conical flask (250ml)
- Glass rod
- Boiling tube
- Dropper
- Burette
- Funnel
- Tripod stand
- Wire gauze
- Iron stand
- Round bottom flask
- Solution of aluminium chloride (2% solution)
- Distilled water
Check Also: Amphoteric Oxides
Procedure
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- A conical flask of 250ml is taken and sterilized under steam. This will remove all the contamination which can become a hindrance in the process.
- Now prepare the 2% solution of aluminium chloride if the stock is not available. To prepare the same add 2g of pure aluminium Chloride in 100mlof distilled water.
- Take 100ml of distilled water in the clean clinical flask and place it over the burner with the wire gauze.
- Add 10ml of the 2% solution of aluminium chloride that you have prepared. Use a dropper or a burette for the same.
- Make sure to stir the solution constantly as you add the aluminium chloride.
- Keep heating the flask until you see a white-colored solution of aluminium hydroxide.
- Then let the flask cool down at room temperature.
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Precaution
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- Make sure to sterilize the equipment.
- To avoid the destabilization of the solution the HCl has to be removed.
Things to Remember
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- Prepare a stock solution of 2% aluminium chloride by adding 2g of pure aluminium chloride in 100ml of water.
- Sterilize all the flasks before use to avoid contamination as this process is sensitive.
- In order to produce aluminium hydroxide on a large scale Bayer’s process is used.
- A white color substance will be formed and aluminium hydroxide is amorphous.
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Sample Questions
Ques: How can you prepare 10% of aluminium chloride? (2 marks)
Ans: To make a solution of 10% aluminium chloride, add 10g of pure aluminium chloride in 100ml of distilled water.
Ques: what does 2% solution mean? (2 marks)
Ans: 2% solution w/v means that 2g of substance is added to 100ml of distilled water.
Ques: What is hydrolysis? (2 marks)
Ans: Hydrolysis is the process of cleavage of chemical bonds when water is added. This can be seen as the opposite of condensation which is the combination to make a larger molecule.
Ques: What is dialysis? (2 marks)
Ans: dialysis is the removal/separation of colloidal particles, by exploiting their rate of diffusion through a semi-permeable membrane.
Ques: what is a lyophobic solution? (2 marks)
Ans: As you know hydrophobic solution hates water, similarly lyophobic solutions are the ones that hate all solvents. aluminium hydroxide is an example of a lyophobic solution They can be easily precipitated if we add a small amount of electrolyte. They cannot form the colloidal solutions once precipitated therefore are irreversible in nature
Ques: What is the color obtained during the formation of aluminium hydroxide? (2 marks)
Ans: a white color will be obtained when the reaction will take place and aluminium hydroxide will be formed.
Ques: What are the properties of aluminium hydroxide? (2 marks)
Ans: aluminium hydroxide is an amorphous powder that is in white color. It is highly insoluble in water but can be dissolved in acidic solutions.
Ques: What is Bayer's process? (3 marks)
Ans: Bayer’s process is the process that is used to make aluminium hydroxide on a commercial scale. In this process, bauxite is dissolved in sodium hydroxide at a temperature of 270 degrees celsius. After the completion of this process, the waste is removed and sodium illuminate solution is allowed to precipitate. In this precipitate, the mineral obtains dis aluminium hydroxide.
Ques: What is calcination? (2 marks)
Ans: The process that is used to form alumina or aluminium oxide from aluminium hydroxide is called calcination.
Ques: How to prepare aluminium hydroxide? (2 marks)
Ans: Add 10ml of 2% solution of aluminium chloride to 100ml of distilled water and heat it. Continuously stir the flask and heat it till a white color product is obtained. Make sure to remove the HCl to avoid hindrance.
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