CBSE Class 12 chemistry practical, Surface chemistry · Physical chemistry experiments
Source: CBSE Class 12 chemistry practical syllabus · use your school laboratory manual (NCERT Lab Manual where your school uses it).
Lyophilic and lyophobic sols (Class 12 chemistry practical)
You prepare one lyophilic and one lyophobic sol using the recipes in your laboratory manual.
Record what you see when each sol is left standing or heated gently — do not copy stability claims from the internet instead of your own notes.
Published practice page. Concentrations, masses, and numerical answers come from your school laboratory manual and your own readings — not invented here. Not yet reviewed by a named chemistry reviewer. Version 1.0.0, updated 2026-10-03.
Safety — read before you start
Safety warning. Practise here. Perform the real experiment only in your school lab, with your teacher present.
- Alkali burns skin and eyes.
- Ferric salts stain and are irritant.
Wear: Lab coat, Splash goggles, Gloves, as your teacher directs.
Follow your teacher’s disposal instructions. Do not pour leftovers down a household drain.
Loads only after you tap. Use the lab hands to pick up and use equipment (pointer hidden in the scene). Falls back to a flat diagram if WebGL is unavailable.
Aim
To prepare lyophilic and lyophobic sols and compare their appearance, ease of preparation, and relative stability as directed in your laboratory manual.
Methods and quantities can differ between schools. Follow your teacher's instructions.
Apparatus and chemicals
| Item | Note |
|---|---|
| Beakers | Clean; grease-free for lyophobic sols. |
| Glass rod | Stirring; avoid scratching beakers. |
| Tripod, gauze, burner (if required) | Only for the heating steps your manual lists. |
| Measuring cylinder / balance | For masses and volumes in your manual. |
| Filter paper and funnel (if required) | Some manuals filter the ferric hydroxide sol. |
| Starch or gum arabic (lyophilic) (starch or gum) | Use the concentration, mass, and volume values printed in your school laboratory manual. This page does not invent a numerical result for you. |
| Ferric chloride solution (FeCl3) | For lyophobic ferric hydroxide sol — strength as in manual. |
| Sodium hydroxide or ammonium hydroxide (NaOH or NH4OH) | Added dropwise to precipitate Fe(OH)₃ and peptise as directed. |
| Distilled water (H2O) | Boiled and cooled if your manual requires it for sol preparation. |
Theory and reaction
Open
A sol is a colloidal dispersion of solid particles in a liquid. Particle size is typically 1–100 nm.
Lyophilic sols form readily when the dispersed phase has a strong affinity for the medium (e.g. starch in water). They are relatively stable and may be re-dispersed after drying in many cases.
Lyophobic sols need a peptising agent or careful technique; particles have little affinity for the medium. They coagulate more easily on heating or on adding electrolytes.
Ferric chloride with alkali gives colloidal ferric hydroxide. Starch disperses in water to give a lyophilic sol.
Procedure
- Prepare the lyophilic sol: dissolve or suspend starch (or gum) in hot distilled water as your manual describes. Cool and note appearance.
- Prepare the lyophobic sol: add ferric chloride solution to boiling distilled water, then add dilute alkali dropwise with stirring until a deep red-brown sol forms.Safety: Alkali and ferric salts are corrosive. Add alkali slowly; a sudden excess can flocculate the sol.
- Compare colour, clarity, and ease of formation in your observation table.
- Leave both sols undisturbed. Note any settling or change after the time your teacher specifies.
- If the manual includes a coagulation test, add a few drops of electrolyte to each sol and record differences.
Observation table
Enter the readings from your school lab in the practical file below. This page does not fill them in for you.
Calculation
No numerical calculation. Comparative observations only.
Result
State which sol is lyophilic and which is lyophobic, with brief evidence from your preparation and stability notes.
Precautions
- Use distilled water when the manual specifies it.
- Add alkali dropwise for ferric hydroxide sol — excess alkali coagulates the sol.
- Do not confuse a true sol with a coarse suspension.
Viva questions
Answer one question at a time. The full answers stay closed until you open them.
Question 1 of 4
Lyophilic sols are characterised by…
Pick an answer first.
Show all questions and answers
Lyophilic sols are characterised by…
Answer: Strong affinity of dispersed phase for the dispersion medium. Reason: The dispersed phase is solvent-loving and often forms more easily.
Lyophobic sols generally…
Answer: Coagulate more readily on adding electrolytes. Reason: They need stabilisation; electrolytes reduce the zeta potential and cause coagulation.
The Tyndall effect is…
Answer: Scattering of light by colloidal particles. Reason: Colloidal particles scatter a beam of light; true solutions do not show it strongly.
Peptisation means…
Answer: Converting a freshly precipitated substance into a colloidal sol. Reason: A precipitate is dispersed to colloidal size with a peptising agent or technique.
Common mistakes
- Calling a cloudy suspension a ‘sol’ without the manual’s peptisation steps.
- Adding cold water to ferric chloride when the manual requires boiling water.
- Skipping the comparison table between the two types.
Frequently asked questions
- Can I do this at home?
- No. Use this page to practise the order of steps and viva. Do the real experiment only in your school laboratory, with your teacher present.
Your practical file
Name, school, and roll number are optional and are not sent anywhere.
The practical file opens on this device.
Review
Not yet reviewed by a named chemistry reviewer. Published for practice only — follow your teacher and laboratory manual for quantities and safety.
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