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).
Dialysis of a sol (Class 12 chemistry practical)
You tie a sol in a semi-permeable bag and suspend it in distilled water.
The sol particles stay inside; small ions diffuse out. Record how you test for removed electrolytes.
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.
- Ferric hydroxide sols and FeCl₃ residues irritate skin and eyes.
- Confirmatory test reagents (e.g. AgNO₃) are toxic — use small volumes under teacher supervision.
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 purify a sol by dialysis using a parchment/cellophane membrane, as described in your laboratory manual.
Methods and quantities can differ between schools. Follow your teacher's instructions.
Apparatus and chemicals
| Item | Note |
|---|---|
| Parchment paper or cellophane bag | Soak as your manual directs before use. |
| Beaker (large) | Holds distilled water for dialysis. |
| Glass rod / thread | To suspend the bag without puncturing it. |
| Test tubes and droppers | For tests on dialysate if required. |
| Prepared sol (sol) | Use the sol you prepared in the lyophilic/lyophobic or ferric hydroxide experiment. |
| Distilled water (H2O) | Change the outer water as your teacher directs. |
| Confirmatory test reagents for ions (test reagents) | e.g. AgNO₃ for chloride if FeCl₃ sol was prepared — only what your manual lists. |
Theory and reaction
Open
Dialysis separates colloidal particles from crystalloids through a semi-permeable membrane.
Colloidal particles are too large to pass through; ions and small molecules diffuse into the outer water.
Repeated changes of outer water improve purification.
Large sol particles stay in the bag; electrolytes diffuse into the surrounding water.
Procedure
- Prepare or obtain the sol your manual specifies. Cool to room temperature if heated.
- Fill the soaked membrane bag partly with sol. Tie securely, leaving space for expansion.
- Suspend the bag in a beaker of distilled water. Leave for the time your manual states.
- Replace the outer water two or three times if directed. Stir the outer water gently only if allowed.
- Test a sample of dialysate for the ion your manual names (e.g. chloride). Record whether the test fades after dialysis.Safety: Test reagents may be toxic — use small volumes.
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 calculation. Qualitative comparison of sol before and after dialysis.
Result
State whether electrolytes were removed from the sol and describe the final appearance of the purified sol.
Precautions
- Do not puncture the bag — sol leaks defeat the purpose.
- Use distilled water in the outer bath.
- Do not squeeze the bag harshly.
Viva questions
Answer one question at a time. The full answers stay closed until you open them.
Question 1 of 4
Dialysis is based on…
Pick an answer first.
Show all questions and answers
Dialysis is based on…
Answer: Diffusion through a semi-permeable membrane. Reason: Small ions pass; colloidal particles remain.
During dialysis of ferric hydroxide sol prepared from FeCl₃, chloride ions…
Answer: Diffuse into the outer water. Reason: Cl⁻ is a crystalloid and leaves through the membrane.
Purification of sols by dialysis is similar in idea to…
Answer: Kidney dialysis in biology. Reason: Both use selective passage through a membrane.
Why change the outer water repeatedly?
Answer: To maintain a concentration gradient for diffusion of electrolytes. Reason: Fresh water keeps driving ions out of the bag.
Common mistakes
- Using tap water and reporting ‘pure’ sol without ion tests.
- Overfilling the bag so it bursts when tied.
- Discarding the sol instead of testing the dialysate.
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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