Use the ethanol emulsion test to detect fats and oils
Choose the reagent, explain the method and interpret controlled observations.
Cross-referenced to the 2028–2029 0653 section using original teaching from the related single-science courses. A 0653-specific objective-by-objective and Core/Supplement review is in progress. Written practice is self-checked and does not demonstrate supervised laboratory competence or award an official Cambridge grade.
Before you begin
- Recall the distinction between an element, a molecule and a cell structure.
Work on paper. Try each question before revealing help, and explain why your method works.
Quick readiness check
What is the target of the Ethanol emulsion test?
What you will learn
- Choose the reagent, explain the method and interpret controlled observations.
- Explain the conclusion from stated evidence and recognise its limits.
Choose the target and method
Ethanol emulsion tests for fats and oils. Mix the sample with ethanol to extract lipid, then add the clear ethanol extract to water. A cloudy white emulsion indicates a positive result. Remove insoluble food debris as specified so it is not mistaken for the emulsion.
The starting or negative appearance is clear; the positive observation is a cloudy white emulsion. Record the observed change before writing a conclusion. A coloured reagent is not automatically a positive result.
Check what the result proves
A known oil provides a positive comparison; a matching reagent blank helps distinguish background cloudiness. Ethanol is flammable and must be kept away from flames.
Use a separate clean sample portion for each test and clean pipettes to avoid contamination. A positive test supports detection of the named target under these conditions; it does not measure the whole nutrient composition. A negative result means the target was not detected by this method, not proof that none exists at any concentration. Practical work needs teacher-approved procedures and supervision; these written exercises do not certify laboratory competence.
Sources for this lesson
Pause and explain
Why is a milky starting food alone not evidence for the claimed conclusion?
Worked example
A properly controlled Ethanol emulsion test gives a cloudy white emulsion. Interpret it.
Show the worked solution
- Identify the reagent and its named target.
- Compare with the positive and negative controls.
- Restrict the conclusion to the target detected.
Answer Fats and oils detected under the stated test conditions.
Try a topic test
Choose Easy, Normal or Difficult. Save your answers and open worked review after finishing.
Test this topic →From guided practice to a new situation
Write your answer and reasoning first. Use a hint only if you are stuck. The model solution is for self-checking; your written work is not automatically marked.
State the target and positive observation of Ethanol emulsion.
Give me a hint
Link reagent to one target.
Compare my reasoning
- Identify fats and oils.
- State a cloudy white emulsion.
Fats and oils; a cloudy white emulsion.
Look for these in your work
- Name the tested target and the observed change.
- Use the correct procedure and comparison when interpreting the result.
After correctly extracting two samples in ethanol and transferring clear extracts into water, S forms a new white cloud while T stays clear. The oil control is cloudy and the reagent blank clear. Interpret S and T.
Give me a hint
Compare the new observations with the working controls.
Compare my reasoning
- S matches the lipid-positive observation.
- T has no newly formed emulsion.
- Sensitivity limits prevent claiming absolute absence.
Lipid was detected in S; lipid was not detected in T under these test conditions.
Look for these in your work
- Use the extract-then-water sequence.
- Restrict the negative claim to detection conditions.
A milky starting sample and the ethanol-water reagent blank are both cloudy. Why is the starting milkiness inadequate evidence, and how should the comparison be improved?
Give me a hint
Separate pre-existing cloudiness from a new test result.
Compare my reasoning
- Starting cloudiness may come from the food before the assay.
- A cloudy reagent blank also prevents a clear negative comparison.
- Use uncontaminated reagents, allow debris to settle and transfer the clear ethanol extract into water; repeat controls.
Do not call the starting milkiness a positive test. Correct the cloudy blank and compare newly formed emulsion from a clear extract with working controls.
Look for these in your work
- Identify both sources of ambiguity.
- Retain extraction before adding the clear extract to water.
Common mistakes
- Starting reagent colours and sample colours can mislead.
- Controls help validate the comparison and procedure.
What can you explain now?
Why is a milky starting food alone not evidence for the claimed conclusion?
Compare with the explanation
The observation must be interpreted using the correct method and controls.
Pre-existing cloudiness is not proof that the ethanol extraction produced an emulsion.
After trying it yourself, choose your next review. This is your self-assessment.
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Make it stick
Recall the target, method, positive change and one control without looking.
If you needed the solution, close it and solve the problem again from a blank page. A correct answer is stronger when you can explain the reason for each step.