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).
Emulsions and emulsifying agents (Class 12 chemistry practical)
You compare a temporary emulsion (oil + water alone) with one stabilised by an emulsifying agent.
Use the oil, soap, and volumes from your laboratory manual.
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.
- Laboratory oils and soap solutions must not be ingested.
- Avoid eye contact with soap or alkaline emulsifier solutions.
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 an emulsion of oil in water, study the action of an emulsifying agent, and note how the emulsion breaks on standing or on adding an electrolyte, as in your manual.
Methods and quantities can differ between schools. Follow your teacher's instructions.
Apparatus and chemicals
| Item | Note |
|---|---|
| Test tubes or small bottles with stoppers | For shaking emulsions. |
| Measuring cylinder | Equal oil and water volumes if the manual says so. |
| Droppers | For soap solution or gum. |
| Edible or laboratory oil (e.g. castor oil) (oil) | Use the concentration, mass, and volume values printed in your school laboratory manual. This page does not invent a numerical result for you. |
| Distilled water (H2O) | Dispersion medium. |
| Soap solution or gum arabic (emulsifier) | Emulsifying agent strength as in manual. |
| Sodium chloride solution (optional) (NaCl) | If manual tests breaking by electrolyte. |
Theory and reaction
Open
An emulsion is a colloid of one liquid dispersed in another (e.g. oil in water, O/W).
Emulsifying agents are often surface-active: they form a film at droplet surfaces and reduce coalescence.
Without a stabiliser, oil and water separate on standing because interfacial tension favours two bulk phases.
Shaking with an emulsifier gives a metastable oil-in-water emulsion.
Procedure
- Measure oil and water as your manual states into a test tube. Stopper and shake. Note how quickly layers separate.
- Repeat with the same volumes plus a few drops of soap or gum solution. Shake equally. Record stability time.
- Identify the continuous phase using the manual’s test (e.g. dilution with water) if provided.
- If directed, add dilute NaCl to the stable emulsion and note whether it breaks.
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. Record relative stability in words or comparative times from your watch.
Result
Conclude whether your emulsion is oil-in-water (or as your tests show) and how the emulsifying agent changed stability.
Precautions
- Use only oils and reagents supplied in the lab.
- Clean stoppers — grease affects emulsion quality.
- Do not ingest laboratory oils or soap solutions.
Viva questions
Answer one question at a time. The full answers stay closed until you open them.
Question 1 of 4
An emulsion is…
Pick an answer first.
Show all questions and answers
An emulsion is…
Answer: A dispersion of one liquid in another. Reason: Two immiscible liquids, one dispersed as droplets in the other.
Soap stabilises an O/W emulsion mainly by…
Answer: Orienting at the oil–water interface. Reason: Surfactant molecules reduce interfacial tension and stabilise droplets.
Milk is often cited as an example of…
Answer: An emulsion (fat in aqueous phase). Reason: Fat globules dispersed in an aqueous phase with natural emulsifiers.
Adding excess electrolyte to a charge-stabilised emulsion may…
Answer: Cause breaking (coalescence) of droplets. Reason: Ions compress the double layer and droplets merge.
Common mistakes
- Unequal shaking effort between ‘with’ and ‘without’ emulsifier tubes.
- Calling any cloudy mixture an emulsion without noting separation.
- Using hard tap water when the manual specifies distilled water.
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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