

An Overview of Class 12 Chemistry To Prepare Ferric Hydroxide Solution Experiment
Colloidal solutions are heterogeneous. They are made up of two components: the dispersed phase or solute and the dispersion medium or solvent. In a colloidal solution, the dispersed phase and dispersion medium do not form a single phase, and hence small or large particles of the solute remain visible in the colloidal solution. There are various types of colloids, one of them being sols. Sols are a type of colloidal solution wherein the dispersed phase is a solid component, and the dispersion medium is liquid. Ferric hydroxide sol is a lyophobic sol wherein the ferric hydroxide is solvent-repelling since it shows a very low affinity towards the dispersed medium. Since water is the dispersed medium, it can also be said that ferric hydroxide sol is hydrophobic. Other examples of lyophobic sols are Aluminum hydroxide and arsenic sulfide.
Table of Contents
Aim
Requirements
Theory
Methodology
Observations
Conclusion
Precaution
Summary
Questions
Aim
To prepare ferric hydroxide Fe(OH)3 sol
Requirements
Beaker(250ml), Glass, rod, filter paper, burner, wire-gauze, Conical flask, tripod stand, stand with clamp, dropper, 2% Ferric chloride solution, distilled water, etc.
Theory
Various metal hydroxides and metal sulfides form a lyophobic sol since they have a very affinity towards the dispersed medium in which they are made. Ferric hydroxide is one such type of lyophobic sol prepared indirectly through hydrolysis using Ferric chloride in boiling distilled water. The reaction for this is as follows-
\(FeCl3 + 3H2O \to Fe(OH)3 + 3HCl\)
Hydrolysis of ferric chloride leads to the formation of insoluble ferric hydroxide particles, which aggregate together, forming larger colloidal particles. The stability of various lyophobic sols is due to the charge present on the outer surface of the colloidal particles.
Procedure
i) Preparation of FeCl3
Weigh 2g of pure FeCl3 in a beaker.
Add 100 ml of Distilled water and dissolve all the FeCl3 into it.
2% Ferric chloride solution is prepared.
ii) Preparation of Fe(OH)3
Take a 250ml conical flask and clean it using the process of steaming out.
Add distilled water to this flask, boil it over a burner, and use a wire gauze.
Take the 2% Ferric chloride solution and add it to the boiling water, drop-wise, using a dropper.
Heat the above flask until a deep red or brown coloured solution of Ferric hydroxide is not obtained. Keep adding extra water when required, as water is lost due to evaporation.
Allow the contents of the solution to come at room temperature. The final ferric hydroxide Fe(OH)3 sol is prepared.
Observations
As the process of hydrolysis begins small colloidal particles of ferric hydroxide appear, and they slowly aggregate and form large colloidal sols. The solution obtained is deep red or brown in colour.
Result
A lyophobic colloidal sol of ferric hydroxide was prepared using the process of hydrolysis.
Precautions
Clean all apparatus before and after use.
Be careful while working near the burner.
Remove the HCl produced in the reaction by the dialysis process.
Add the ferric chloride solution dropwise into boiling water.
Wear all the other safety gear such as lab coat, gloves etc., while working in a laboratory.
Lab Manual Questions
1. By which method ferric hydroxide colloid is prepared?
Ans: Ferric Hydroxide is a colloidal solution which is prepared indirectly through the process of hydrolysis of Ferric chloride. Boiling water is used for this purpose, and the final product is insoluble ferric hydroxide particles.
2. Describe different types of colloidal solutions.
Ans: There are 4 types of colloidal sols-
Sols- The dispersed medium is water and the dispersed phase is a solid.
Emulsions-Both dispersed medium and dispersed phase are liquid.
Foam- Here, the dispersed phase is gas, and the dispersed medium is solids or liquids.
Aerosols- Here, the dispersed phase is solid or liquid, and the dispersed medium is gas.
3. Why does HCl have to be removed during the formation of ferric hydroxide?
Ans: As a by-product of the hydrolysis reaction (HCl), hydrochloric acid is formed. This HCl destabilises the colloidal sol and hence needs to be removed from the colloidal solution, or a stable solution will not be obtained.
4. What is the charge of Fe(OH)3 sol?
Ans: Fe(OH)3 sol particles formed after hydrolysis undergo a process of agglomeration and form large colloidal particles Fe3+ ions are absorbed by the colloidal particles giving them a positive charge on their surface.
Viva Questions
1. Fe(OH)3 chemical name is?
Ans: Fe(OH)3 stands for ferric hydroxide. It is a deep red or brown colloidal solution.
2. What are the qualities of a true solution?
Ans: True solutions are –
Homogenous i.e. the solute particles completely dissolved in the solvent and hence form a solution.
They are in a single phase
They do not have any suspended particles. eg. NaCl in water.
3. What are the components of a solution?
Ans: A solution is made of solute and a solvent.
4. Which process is used for purifying the Fe(OH)3 Sol?
Ans: The dialysis process is used for purifying the Fe(OH)3 Sol. This is done by removing HCl generated post the reaction.
5. What is hydrolysis?
Ans: A chemical reaction which leads to the decomposition of reactants and water is known as hydrolysis. Water is used for the breakage of reactants and for forming the end products.
6. What is agglomeration?
Ans: Agglomeration is a process of combination of two or more particles to form a larger particle or a combination of particles to form a larger mass.
7. What is dialysis?
Ans: The process of separating ions or molecules from the colloidal solutions is known as dialysis. It happens through the process of diffusion.
8. What is lyophobic sol and lyophilic sol?
Ans: Sols in which solute particles have a weak affinity towards the dispersion medium are known as lyophobic sols. Sols in which solute particles have a strong affinity towards the dispersion medium are known as lyophilic sols.
9. How HCl is formed while preparing ferric hydroxide Fe(OH)3 sol?
Ans: During the hydrolysis reaction Fe3+ combines with the OH- of the water molecule forming the ferric hydroxide. The remaining H+ and Cl- ions combine and form HCl.
10. Give examples of foam types of colloidal solutions.
Ans: Examples of foam-type colloids are whipped cream, shaving cream, soap lather etc.
Practical Based Questions (MCQs)
1. What is the ferric hydroxide formula?
Fe(OH)3
FeOH
Fe2OH2
FeOH2
Ans: Fe(OH)3
2. Lyophobic colloids can be prepared by
Boiling water
Add the constituents slowly while constantly stirring
Take ice cold chilled water and then adding the constituents while stirring
Both A and B
Ans: Both A and B
3.______is a universal solvent
Alcohol
Glycerin
Water
Esters
Ans: Water
4. Hydro means______and Lysis means____
Water, Breakage
Breakage, Water
Liquid, Joining
Solvent, Reformation
Ans: Water, Breakage
5. State which of the following are true-
Ferric chloride is positive charged sol
Ferric hydroxide sol is positively charged
Starch sol is positively charged
Lyophobic are solvent loving
Ans: Ferric hydroxide sol is positively charged
6. One molecule of Fe(OH)3 requires_____and _____
FeCl3,H2O
3H2O, FeCl3
3FeCl3, 4H2O
4H2O, 2FeCl3
Ans: 3H2O, FeCl3
7. What is by-product during the formation of Ferric hydroxide?
Sulfuric acid
Nitric acid
Hydrochloric acid
Sodium Hydroxide
Ans: Hydrochloric acid
8. HCl is a strong ___and can donate _____H+ ions
Acid, 1
Acid, 2
Base, 1
Weak acid, 1
Ans: Acid, 1
9. What is another name for ferric hydroxide?
Iron dihydrate
Ion trihydrate
Ferrous hydroxide
Iron hydroxide
Ans: Iron hydroxide
10. Find the odd man out
Margarine
Ice cream
Mayonnaise
Brine solution
Ans: Brine solution
Summary
In a colloidal solution the solute remains suspended in the solvent. Colloids are of various types depending on the dispersed phase and the dispersion medium used. Lyophobic Sols are a type of colloidal solution wherein the solid dispersed phase has less affinity towards the liquid dispersion medium. Ferric hydroxide is one such example of Lyophobic sols. It is prepared by hydrolysis of ferric chloride with boiling water. Ferric hydroxide is a dark red or brown coloured solution which has various applications in industries and chemical labs.
FAQs on Class 12 Chemistry To Prepare Ferric Hydroxide Solution Experiment
1. How do you prepare ferric hydroxide sol in a laboratory for the CBSE Class 12 Chemistry practical exam 2025-26?
The preparation of ferric hydroxide sol is a standard experiment based on the principle of hydrolysis. The step-by-step procedure is as follows:
- Take about 100 mL of distilled water in a clean beaker and heat it to boiling.
- In a separate test tube, prepare a 2% solution of ferric chloride (FeCl₃) by dissolving about 2g of solid FeCl₃ in 100 mL of distilled water.
- Using a dropper, add the ferric chloride solution drop by drop to the boiling distilled water while continuously stirring.
- Continue heating until a deep reddish-brown sol of ferric hydroxide is formed.
The chemical reaction involved is: FeCl₃ (aq) + 3H₂O (l) → Fe(OH)₃ (sol) + 3HCl (aq).
2. Why is the ferric hydroxide sol prepared in the experiment positively charged? Explain the mechanism involved.
Ferric hydroxide sol is positively charged due to the process of preferential adsorption of ions from the dispersion medium. The Fe(OH)₃ particles formed during hydrolysis adsorb the positively charged Ferric ions (Fe³⁺) from the ferric chloride solution. This forms a fixed positive layer around the colloidal particles, resulting in an overall positive charge on the sol: [Fe(OH)₃]Fe³⁺.
3. Is ferric hydroxide sol a lyophilic or a lyophobic sol? Justify your answer based on its preparation and stability.
Ferric hydroxide sol is a lyophobic sol (solvent-hating). This is because:
- Preparation Method: It is prepared by an indirect method (hydrolysis of FeCl₃), not by simply mixing with the solvent.
- Stability: It is inherently unstable and requires the presence of a charge on its particles for stability. It can be easily coagulated by adding a small amount of an electrolyte, which neutralises this charge.
4. What is the significance of the 'steaming-out' process and using boiling water for this experiment?
Both steps are crucial for forming a stable sol.
- The steaming-out process ensures that the apparatus is completely clean and free from any ionic impurities that could cause premature coagulation of the sol.
- Using boiling water is essential because the hydrolysis of ferric chloride is highly favoured at high temperatures. This ensures a complete reaction to form the Fe(OH)₃ colloidal particles. Using cold water would result in an incomplete or very slow reaction.
5. From an exam point of view, why is arsenious sulphide (As₂S₃) sol negatively charged, while ferric hydroxide sol is positively charged?
This is a classic comparison question based on preferential adsorption.
- Ferric Hydroxide Sol [Fe(OH)₃]: As explained, it is formed by the hydrolysis of FeCl₃. The Fe(OH)₃ particles preferentially adsorb Fe³⁺ ions, making the sol positive.
- Arsenious Sulphide Sol [As₂S₃]: It is prepared by passing H₂S gas through a solution of arsenious oxide. The As₂S₃ particles preferentially adsorb Sulphide (S²⁻) ions from the medium, making the sol negative.
6. According to the Hardy-Schulze rule, which electrolyte would be more effective in coagulating ferric hydroxide sol: NaCl or K₂SO₄? Explain why.
According to the Hardy-Schulze rule, the coagulating power of an ion is directly proportional to the magnitude of its charge. Since ferric hydroxide sol is positively charged, it will be coagulated by negative ions (anions). The two electrolytes provide Cl⁻ and SO₄²⁻ ions. As the sulphate ion (SO₄²⁻) has a greater negative charge (-2) compared to the chloride ion (Cl⁻) (-1), K₂SO₄ will be significantly more effective in coagulating the positive ferric hydroxide sol.
7. What would happen if the HCl formed during the preparation of ferric hydroxide sol is not removed?
The hydrochloric acid (HCl) formed is an electrolyte. If it is not removed (through a process like dialysis), its concentration will destabilise the sol. The excess ions (H⁺ and Cl⁻) would neutralise the positive charge on the colloidal particles, causing them to coagulate and precipitate out of the solution, thus destroying the sol. Therefore, purification is a vital step for long-term stability.

















