Why does ordinary oil float above water when left in a glass, while mayonnaise can remain thick, creamy and fairly uniform despite containing a large amount of oil? A Secondary 1 pupil might say that the oil has completely dissolved into vinegar or that the white colour proves it has turned into a new pure compound. The better Science question is how can a liquid that does not mix readily with water be divided into countless tiny droplets and kept from joining together again?
For families searching for a Secondary 1 Chemistry Tutor Hougang, the immediate answer is that mayonnaise is an oil-in-water emulsion. Mixing breaks the oil into many small droplets dispersed throughout an aqueous phase. Egg-yolk components such as lecithin and proteins act as emulsifiers, helping stabilise the oil–water interfaces, while the high fraction of dispersed oil droplets creates a thick texture. The oil has not dissolved molecularly into water, and the mixture is not permanently immune to separating: stability depends on droplet size, formulation, processing and storage.
- Immediate explanation: microscopic droplets of oil remain dispersed in a water-rich phase with the help of interfacial emulsifying ingredients
- Key ingredients: oil is the dispersed phase; water and vinegar contribute to the continuous phase; egg-yolk phospholipids and proteins help stabilise the interfaces
- Why thick: high droplet volume fraction, interactions and structure can make mayonnaise resist flow much more than plain oil or water
- Not the same as dissolving: droplets remain distinct microscopic regions, even when the sauce looks smooth and uniform
- What may go wrong: droplets can join or the emulsion can separate when formulation, processing or storage is unsuitable
- Safe school learning: use diagrams, micrographs and teacher-supplied data; raw-egg preparations and unknown foods are not needed for experiments
1. Begin with two distinct observations
A glass containing shaken oil and water may separate into layers after standing. A jar of properly formulated mayonnaise can remain thick and more uniform. The two products show different behaviour despite both containing oil and water.
The pupil should not say only that mayonnaise is sticky. The scientific problem concerns the location of the oil and the factors that stop microscopic droplets merging rapidly.
2. What is an emulsion?
An emulsion is a dispersion of small droplets of one liquid in another liquid with which it is not freely miscible. A typical mayonnaise is an oil-in-water emulsion rather than a molecular solution.
The UCLA organic chemistry glossary explicitly classifies mayonnaise as an emulsion stabilised by egg lecithin. A first-year learner should distinguish a dispersed droplet from one dissolved molecule.
3. What does dispersed mean?
A dispersed phase consists of droplets or particles distributed throughout a continuous material. In mayonnaise, oil droplets form the dispersed phase, and the aqueous phase surrounds them.
A diagram should not show one large oil layer on top of water as the structure of finished stable mayonnaise. That would represent the un-emulsified starting condition.
4. What is a continuous phase?
The continuous phase extends around the dispersed droplets. In common mayonnaise, water from the ingredients and vinegar forms the major water-rich continuous environment.
Even though oil can dominate by volume, the emulsion can still be called oil-in-water because water occupies the continuous regions separating droplets. Volume fraction and continuous-phase identity are distinct concepts.
5. Why oil and water normally separate
Water molecules are polar and have strong favourable interactions with one another. Most edible oils are made of comparatively nonpolar triglyceride molecules that do not mix freely on the molecular scale with water.
Separating into layers reduces the extent of energetically unfavourable oil–water interface for an un-stabilised mixture. The exact behaviour also depends on density, mixing and other ingredients.
6. The molecular structure of water matters
Water is a small polar molecule whose interactions include hydrogen bonding. Its physical properties differ from those of long hydrocarbon-rich regions in many triglycerides.
A pupil need not draw all electron orbitals to understand the comparison. The important fact is that molecular composition changes which interactions are energetically favourable.
7. Edible oils contain triglycerides
Typical cooking oils contain large amounts of triacylglycerol molecules with fatty-acid-derived chains. These chains have extensive nonpolar regions that contribute to the oil’s poor mixing with water.
The word oil does not identify one pure chemical. Mayonnaise recipes use different oil types whose detailed composition can influence flavour, stability and other properties.
8. Miscible and immiscible are useful words
Miscible liquids mix into one liquid phase over a relevant composition range. Immiscible or poorly miscible liquids prefer separate phases under the stated conditions.
A first-year student should not interpret immiscible as meaning no molecules ever cross the interface. It means the macroscopic liquid phases do not form a single freely mixed solution.
9. What agitation does initially
Stirring, whisking or industrial mixing can break a larger oil region into many small droplets. The new droplet surfaces create much more oil–water contact area.
But mixing alone may not create a durable emulsion. Without suitable stabilisation, droplets can collide and merge after the mechanical force stops.
10. Why small droplets matter
Dividing a fixed oil volume into smaller droplets creates more total interfacial area. A high number of small droplets can help produce an even, creamy-looking dispersion.
Droplet size and distribution also affect viscosity and separation. A student should not say that all droplets are exactly the same diameter because mayonnaise looks uniform to the eye.
11. Why oil droplets want to merge
Oil–water interfacial contact carries an energetic cost. Two droplets that coalesce can reduce the total interface area, depending on conditions. Without stabilising mechanisms, the emulsion may separate over time.
This is why an un-stabilised shaken oil-and-water mixture may not remain uniform. The relevant driving forces are interfacial, not oil molecules consciously trying to escape.
12. What coalescence means
Coalescence occurs when separate droplets meet and merge into a larger drop. Repeated coalescence can eventually produce larger oil-rich regions and visible separation.
A pupil should distinguish droplets colliding from droplets actually merging. A stable emulsion may contain many collisions without each collision resulting in coalescence.
13. What an emulsifier does
An emulsifier contains molecular features that interact favourably with both phases or helps stabilise their interface in other ways. It can lower interfacial tension and provide barriers that reduce droplet merging.
The purpose is not to convert every oil molecule into water. It is to help maintain the dispersed structure of two otherwise poorly miscible liquids.
14. Egg yolk supplies useful emulsifiers
Egg yolk contains phospholipids, including lecithin components, and proteins that help stabilise oil droplets in mayonnaise. Different formulations may also include other emulsifiers or thickeners.
The University of Michigan’s chemical engineering encyclopedia describes egg yolk as a key emulsifying ingredient in mayonnaise. The exact composition varies across recipes and commercial products.
15. What lecithin means
Lecithin is a term often used for mixtures of phospholipids rather than one universal pure molecule. The molecules can have polar regions and nonpolar hydrocarbon-rich chains.
This structure allows them to associate with both watery and oily environments. Students should not memorise a single chemical formula for all lecithin materials.
16. Amphiphilic molecules
An amphiphilic molecule has parts with different affinities for water and oil-like environments. Such architecture can help the molecule position itself at the oil–water interface.
A simple diagram shows a polar head facing water and nonpolar tails interacting with the oil droplet. It is a model, not a claim that each molecule has a visible coloured head and body.
17. What happens around an oil droplet
Suitable emulsifying molecules can form an interfacial layer around droplets, making it harder for two bare oil surfaces to join. Proteins can also contribute protective interfacial films.
The droplet remains an oil-rich region, not a giant molecule completely dissolved in water. That is the central structural difference between an emulsion and a true solution.
18. Electrostatic and steric stability
Some emulsions are stabilised by electrical repulsion between interfaces, by physical barriers from adsorbed molecules, or by combinations of effects. The detailed balance varies with the formulation.
These are advanced concepts, but the beginner’s picture is simple: droplet surfaces are modified so they do not merge as readily when they approach one another.
19. How pH can affect the system
Acidity can change the charge and behaviour of some proteins and other emulsifying components. Vinegar or lemon-derived acidity may therefore influence emulsion stability as well as flavour and preservation properties.
A student should not conclude that adding unlimited acid always improves a mayonnaise emulsion. Ingredient ratios and safe formulation limits matter.
20. Why vinegar is not the emulsifier by itself
Vinegar provides a water-based acidic component, but ordinary oil and vinegar still tend to separate if not properly emulsified. Egg-yolk components or other stabilisers play a major role in mayonnaise.
This is a useful contrast with vinaigrette, whose stability depends on formulation and mixing. The mere presence of vinegar does not convert the oil into a water-soluble substance.
21. Why mustard can help some emulsions
Mustard formulations may contain compounds and dispersed materials that help stabilise oil–water interfaces. Their effects depend on the specific condiment and recipe.
The Yale National Initiative’s emulsion teaching material describes everyday condiments as examples of stabilisation. The learning point is that one product may contain several cooperating emulsifying ingredients.
22. What proteins contribute at interfaces
Proteins can interact with oil and water and form films around droplets. Their structure and charge influence how well they stabilise an emulsion under given conditions.
An egg-yolk protein does not need to become a fat molecule to assist an oil droplet. The chemical properties of different regions of a protein matter.
23. Why mayonnaise can be very thick
In mayonnaise, the oil droplets can occupy a large fraction of the volume. Crowded droplets affect each other’s ability to move, producing high apparent viscosity and, in some products, a yield stress.
This is more precise than saying the oil froze. The droplets remain liquid while their collective arrangement makes the emulsion resistant to flow.
24. What viscosity means
Viscosity is resistance to flow under defined conditions. Mayonnaise often flows much less readily than water because of its dispersed structure and the interactions among droplets.
Viscosity depends on temperature and measurement method. A first-year pupil can describe that the same spoon moves differently through the two materials without numerical formulas.
25. What yield stress means
Some thick emulsions can resist small applied stresses without flowing much, then begin moving when the applied force exceeds a threshold. Mayonnaise can show this soft-solid-like behaviour.
A jar’s ability to hold a spoon mark is therefore not proof that the oil became a crystalline solid. It reflects the collective mechanical properties of the concentrated emulsion.
26. Why high oil fraction can thicken rather than thin
Oil by itself is a flowing liquid. But when finely dispersed droplets occupy much of a continuous phase, they can crowd and deform, increasing the mixture’s resistance to motion.
This is a surprising structure–property lesson. More of one liquid can produce a product that flows less easily because the phase arrangement changed.
27. Why the oil’s amount has limits
An emulsion formulation can fail if too much oil is added relative to available interfacial stabilisation or if mixing is unsuitable. Droplets may coalesce and form separated phases.
A pupil should not infer that adding unlimited oil will make mayonnaise infinitely thick and stable. The desired composition lies within a workable range.
28. What a split emulsion looks like
A broken emulsion can show visible oily regions and a thinner watery phase. That suggests the originally dispersed droplet structure has changed, but not necessarily that every oil molecule underwent a chemical reaction.
The dominant event can be physical coalescence and phase separation. This is a useful contrast with chemical oxidation of cooking oil.
29. Why mayonnaise is not permanently stable
Commercial mayonnaise may be quite stable under its intended storage conditions, but emulsion stability has limits. Temperature, formulation, mechanical history and product ageing can affect performance.
The word stable is comparative and time-dependent. It should not be turned into the absolute claim ‘mayonnaise can never separate’.
30. Creaming and separation are different processes
In an emulsion, droplets may migrate under gravity or other forces before they coalesce. Concentration gradients can therefore develop without every droplet merging immediately.
A student should distinguish creaming or droplet redistribution from coalescence and complete phase separation. Different observations require different explanations.
31. Why oil density matters
Many edible oils have lower density than water-rich phases. In an unstable mixture, buoyancy can cause oil-rich regions or droplets to move relative to the surrounding liquid.
This helps explain layers in a simple oil–water glass, but the speed of separation also depends on droplet size, viscosity and stabilising interfaces.
32. Why small droplets can separate slowly
Smaller droplets often move slowly through a viscous continuous phase under gravity. Interfacial stabilisers also reduce coalescence, improving the apparent stability of the mixture.
The student should not infer that tiny droplets alone guarantee stability forever. Both mechanical motion and molecular interactions must be considered.
33. Droplet size distribution
A real emulsion contains droplets with a distribution of sizes. This distribution can influence appearance, flow and how readily the material separates over time.
A microscopic image of one region is a sample rather than a complete guarantee about the whole jar. Scientific measurements need representative sampling.
34. A creamy appearance arises partly from scattering
Microscopic oil droplets and other structures redirect incoming visible light, helping make mayonnaise appear pale or creamy rather than transparent.
This links to Why Milk Looks White. Both are dispersions that scatter light, but their formulations, droplet concentrations and purposes differ.
35. Creamy colour does not prove composition
An off-white sauce can look like mayonnaise without containing egg yolk or having the same emulsion structure. Colour alone is insufficient to identify one emulsifier.
The student should ask for ingredient information and, if necessary, material measurements rather than infer a product’s composition from appearance.
36. What a microscopic cross-section shows
A diagram of oil-in-water mayonnaise should show many oil droplets within a continuous aqueous phase. Emulsifier molecules or proteins sit near the boundaries between them.
Avoid drawing a layer of oil floating separately on top of another layer while calling it a stable emulsion. The picture must match the system being explained.
37. Contrast with a micelle
A micelle formed by surfactants is a different assembly from a relatively large oil droplet stabilised by emulsifiers. Both can include amphiphilic molecules, but their structures are not automatically identical.
A pupil who has studied dishwashing liquid should not call every mayonnaise droplet a detergent micelle. The dispersed phase and geometry matter.
38. Emulsifier and surfactant overlap in function
Many emulsifiers have surface-active properties, reducing interfacial tension or stabilising interfaces. But commercial formulations also rely on viscosity and protein-film effects.
The functional term describes what a component does in a particular system. It does not imply one universal molecule is used in dish soap, milk and mayonnaise.
39. Does emulsification create a new compound?
Mixing oil and water into droplets does not necessarily produce a new pure chemical compound. It changes the physical organisation of a multi-component mixture.
Other chemical changes can occur in foods during processing, but the basic emulsion formation is principally a dispersion and interface-stabilisation process.
40. Why an emulsion is not a solution
In a true solution, solute species are molecularly or ionically dispersed at much smaller scales. In an emulsion, liquid droplets remain as separate microscopic regions.
That structural distinction explains why the same two materials may look uniform but behave differently. A student should understand the scale of mixing, not just the word homogeneous.
41. What stability tests might measure
Food scientists measure droplet size, phase separation, viscosity and other properties under controlled conditions to characterise an emulsion. Each test answers a different question.
A photograph of a smooth jar cannot establish every important property, just as a dark oil sample cannot reveal all oxidation products without analysis.
42. A fictional separation-index dataset
Imagine a teacher gives percentage of separated oil after a defined time: 1%, 3%, 10% and 24% for four formulations. The first appears more resistant to separation under that test.
These numbers are invented for classroom reasoning. They do not establish microbial safety, flavour or suitability for one particular commercial recipe.
43. Compare two droplet sizes
Suppose an emulsion with smaller droplets shows less visible separation than another with larger droplets under a matched test. That is consistent with slower movement and stabilisation, but does not reveal all interfacial chemistry.
A strong conclusion identifies the possible mechanisms and asks what was controlled. Droplet size alone is not the complete stability formula.
44. A fictional viscosity table
A worksheet compares water at 1 relative unit, plain oil at 60 and a thick emulsion at 800 under a single defined measurement method. The emulsion resists flow much more.
The data are illustrative, not official values for mayonnaise. They show that combining two flowing liquids into a dense emulsion can lead to a very different rheological response.
45. Calculate a separation change
If a separated fraction rises from 5% to 12%, that is a 7-percentage-point increase. Relative to the starting 5%, it is a 140% increase.
A pupil should not report that 7 grams of oil were lost without knowing total amount and how the fraction was measured.
46. Why a pale colour is not a safety measure
A mayonnaise product can remain pale and creamy even if its storage history is unsuitable. Microbial safety and ingredient handling are separate issues from emulsion structure.
Food safety must follow the product’s use and storage instructions. A home-created raw egg mixture should not be used as an experiment for children.
47. Raw eggs and foodborne illness
Recipes involving raw or undercooked eggs may carry foodborne pathogen risks, including Salmonella, depending on source and handling. Commercial products have specific safety controls and formulations.
This guide explains the emulsion without providing a raw-egg preparation procedure. A pupil can use micrographs and scientific diagrams instead.
48. Why acidity is not an automatic guarantee
An acidic mayonnaise formulation may inhibit some microorganisms under specified conditions, but a generic splash of vinegar does not guarantee a homemade mixture is safe.
A Chemistry explanation of pH and emulsion stability does not replace validated food-processing and storage procedures. Keep the topics distinct.
49. Why labels matter for egg-free mayonnaise
Some egg-free products use plant proteins, starches or other emulsifiers. They can be designed to resemble mayonnaise in appearance and texture while having different component chemistry.
A good student distinguishes the functional role of an emulsifier from the ingredient’s origin. Egg yolk is common, not the only possible way to stabilise an oil-in-water emulsion.
50. Mayonnaise and milk are related but distinct
Both contain dispersed fat-rich droplets in a watery environment and can scatter visible light. Milk is generally much more dilute in fat droplets than concentrated mayonnaise, and it also contains prominent casein micelles.
This helps explain their very different flow properties. Calling both emulsions is a starting classification rather than a guarantee of equal viscosity or texture.
51. Mayonnaise versus vinaigrette
A simple oil-and-vinegar dressing may separate after standing, while a stabilised mayonnaise can remain uniform much longer because of emulsifiers and its concentrated droplet structure.
Both contain oil and an aqueous acidic phase; the difference lies substantially in formulation and how the droplets are stabilised.
52. Mayonnaise versus chocolate
Chocolate can contain solid particles dispersed in a fat-rich phase, whereas mayonnaise is a concentrated oil-in-water emulsion. Their continuous phases and microstructures differ substantially.
A creamy mouthfeel or pale colour does not prove an identical colloidal system. See Why Chocolate Turns White for a distinct food-material problem.
53. How air bubbles complicate some foods
Some sauces can also contain entrained gas bubbles. An emulsion containing oil droplets is not automatically a foam, although one food product can contain several dispersed phases.
A student should name the dispersed material—liquid oil or gas—before choosing the term emulsion or foam.
54. Why motion can matter after storage
Stirring a separated sauce can redistribute phases temporarily, but the original stability depends on its emulsifiers and structure. A mixture that separates repeatedly may not regain its intended properties automatically.
A school worksheet can ask whether the proposed action changes droplet size, chemistry or simply temporarily mixes the layers.
55. An exam-style explain answer
Question: ‘Why does mayonnaise stay creamy instead of rapidly separating like shaken oil and water?’ Answer: Oil is dispersed as small droplets in a water-rich phase, while lecithin and other egg-yolk components help stabilise the droplet interfaces and reduce coalescence.
A weak answer says the oil dissolved chemically into water. The correct explanation identifies a dispersed phase, continuous phase and interfacial stabilisation.
56. An exam-style comparison
Question: ‘Compare mayonnaise with a mixture of oil and water after standing.’ The unstable mixture may form separate layers, while properly stabilised mayonnaise maintains many tiny oil droplets throughout its water-rich phase.
Both start with poorly miscible liquids. The different microstructure and emulsifiers explain the contrasting appearance.
57. A changed-case prediction
Question: ‘If an emulsion has insufficient stabilising material, what might happen?’ Droplets may coalesce more readily, creating larger oil-rich regions and eventual phase separation.
The precise rate depends on formulation and environment, so a qualitative prediction is more defensible than inventing a fixed time.
58. A question about high oil content
Question: ‘Why is mayonnaise thick even though oil and water can both flow?’ Closely packed, stabilised droplets interact and make the emulsion resist deformation and flow.
This is a microstructure explanation. The oil does not have to freeze into a hard solid for viscosity to increase.
59. G1: phases and particles
For G1, draw many oil droplets held in a continuous water-rich liquid. Explain that a suitable emulsifier helps the droplets stay separated longer.
Use the MOE G1 lower-secondary Science syllabus; surface-energy calculations are enrichment when outside the course.
60. G2: emulsifier structure and a fair test
A G2 learner can describe oil, water and an amphiphilic emulsifier, then interpret a simple separation-index table and identify the controlled variables.
The MOE G2/G3 lower-secondary Science syllabus provides the appropriate curriculum framework.
61. G3: interfaces and concentrated dispersions
A secure G3 learner can discuss interfacial tension, lecithin adsorption, droplet packing and emulsion failure, and explain why a viscosity reading is not the same as microbial safety.
A changed example involving egg-free mayonnaise tests the functional role rather than the identity of one ingredient.
62. A 90-minute small-group lesson
Minutes 0–10: Ask why mayonnaise differs from oil and water. 10–25: Identify dispersed and continuous phases. 25–40: Draw lecithin at an oil–water interface. 40–55: Explain coalescence and droplet crowding.
55–70: Interpret fictional separation and viscosity tables. 70–80: Correct raw-egg safety and dissolution misconceptions. 80–90: Each pupil answers a changed emulsion example independently.
63. A parent diagnostic
One child may believe mayonnaise is an ordinary solution, another may know emulsion but not explain lecithin, while a third may confuse thickness with chemical bonding of all the oil.
Each requires a different teaching step. A small group should not stop when one pupil gives the right paragraph; every learner needs an independent changed-case answer.
64. One-week spaced practice
Day 1: Draw the oil droplets. Day 3: Recall why lecithin is amphiphilic. Day 5: Compare mayonnaise with oil and vinegar. Day 7: Read a new separation graph and explain its limitations.
The 20-minute Science Revision Plan provides a manageable structure for retrieval.
65. Why this is useful beyond mayonnaise
Cosmetics, medicines, paints and other manufactured products can contain emulsions. Their intended functions and safe formulations differ, but stabilising an interface is a recurring materials-science challenge.
A confident learner can apply the droplet-and-emulsifier model to a new system while checking which phase is continuous and which materials are present.
66. Frequently asked questions
Why does mayonnaise not separate quickly? Emulsifiers stabilise small oil droplets in a water-rich phase. Is the oil dissolved? No. Why thick? Crowded droplets and interactions. Can mayonnaise separate? Yes.
Is every mayonnaise egg-based? No. Does emulsion stability prove food safety? No. Should children prepare raw-egg samples for this lesson? No.
67. Source: UCLA chemistry glossary
The UCLA Illustrated Glossary of Organic Chemistry: Emulsion names mayonnaise as an oil-in-water emulsion stabilised by lecithin and distinguishes dispersions from solutions.
This source is particularly useful for the beginner’s classification. The concept should be tied to visible droplets and molecular interfaces rather than copied as a one-sentence definition.
68. Source: chemical engineering and food science
The University of Michigan Visual Encyclopedia: Condiments explains egg yolk’s emulsifying function in mayonnaise. Mississippi State University Extension: Emulsions also describes the role of lecithin and polar/nonpolar groups.
These references provide scientific context; the article deliberately does not require children to make raw-egg mayonnaise as a practical demonstration.
69. The relationship with other Hougang Chemistry topics
Read Why Oil and Water Do Not Mix, Why Milk Looks White, Why Dishwashing Liquid Removes Grease and Why Cooking Oil Turns Rancid.
The different articles separate immiscibility, colloidal scattering, surfactant cleaning and lipid oxidation from the specific stabilisation of mayonnaise.
70. Why one word should not replace explanation
Emulsion is a correct classification, but telling a student ‘mayonnaise stays together because it is an emulsion’ merely renames the observation.
The complete explanation names oil droplets, continuous watery phase, emulsifying molecules at the interfaces and why they reduce droplet merging. Those connections can be tested with a new food example.
71. An evidence-limit case study
Two sauces have nearly identical white colour but different stability after storage. The photograph cannot prove their lecithin concentration or oil fraction. A proper study needs ingredient and droplet information.
The student should identify what measurement would help: droplet-size distributions, phase-separation tests, formulation records or suitable microscopy. Different tests answer different scientific questions.
72. Final parent-facing explanation
A concise answer is: ‘Mayonnaise consists of microscopic oil droplets dispersed in a water-rich phase. Egg-yolk lecithin and other stabilising components help protect the oil–water boundaries from merging, while tightly packed droplets make the sauce thick. It remains an emulsion, not a true molecular solution.’
Then change the example to egg-free mayonnaise and ask what could provide the emulsifying function instead. That checks whether the child learned a material role, not merely an ingredient name.
73. The Hougang Chemistry learning hub
The Hougang Chemistry Tutor Library connects material properties, mixtures, particles and later Chemistry pathways. Use the student’s actual G1, G2 or G3 school topics to decide what to assess.
The final question is why a high amount of liquid oil can produce a thick food when dispersed into many stable microscopic droplets. Answering it is evidence of true structure–property understanding.
28 Worked Questions and Independent Checks
What type of mixture?
Mayonnaise is usually an oil-in-water emulsion. Check: droplets remain distinct microscopic regions.
Which is dispersed?
Oil forms many small droplets. Check: it is not fully molecularly dissolved in vinegar.
Which is continuous?
The aqueous phase containing water and acid. Check: continuous does not necessarily mean most by volume.
What is lecithin?
A mixture of amphiphilic phospholipids that helps stabilise oil–water interfaces. Check: not one universal pure molecule.
What does amphiphilic mean?
It has regions interacting differently with water and oil. Check: the molecule can locate at their boundary.
Why separate without emulsifier?
Droplets may coalesce and reduce unstable interface area. Check: no need for one pure chemical reaction.
What is coalescence?
Two droplets merge into a larger droplet. Check: not every collision ends in coalescence.
Why does mayonnaise look uniform?
Many tiny droplets are distributed throughout a phase. Check: macroscopically uniform need not mean a true solution.
Why can it look pale?
Droplets and other structures scatter visible light. Check: colour does not prove chemical identity.
Why thick?
High droplet concentration and interactions increase resistance to flow. Check: the oil need not freeze.
What is viscosity?
Resistance to flow under defined conditions. Check: measurement conditions matter.
Does oil dissolve into water?
Not in the way a true molecular solute does. Check: an emulsion has a separate dispersed liquid phase.
Can mayonnaise split?
Yes, if droplets coalesce or phases redistribute under unsuitable conditions. Check: no emulsion lasts forever.
Must mayonnaise contain egg?
Not always; other emulsifiers can stabilise particular formulations. Check: identify the function.
What does vinegar contribute?
Water and acidity among other properties. Check: vinegar alone need not stabilise every oil mixture.
How does this differ from milk?
Both are emulsions, but oil fraction, protein colloids and viscosity differ. Check: same classification does not imply same structure.
What is the independent variable?
If testing egg-yolk concentration, that is a changed formulation factor. Check: keep conditions comparable.
What is measured?
Droplet size, separation or viscosity under a defined method. Check: choose the property the question asks.
Calculate an increase
Separated fraction rises from 4% to 9%: five percentage points. Check: it is not five grams without a mass.
Calculate a relative rise
From 4% to 9% is a 125% increase relative to 4%. Check: name the denominator.
What if droplets are larger?
They may separate faster under some conditions, but formulation matters. Check: a prediction needs controls.
Why not raw egg experiments?
Foodborne illness risks require appropriate product and food safety. Check: diagrams and data are sufficient.
G1 response
Draw oil droplets in water and show emulsifier at the boundary. Check: the model is not a molecular solution.
G2 response
Compare an unstable mixture with a stabilised emulsion. Check: use the same materials as far as possible.
G3 response
Explain lecithin, interfacial stability and droplet packing. Check: viscosity is not a food-safety certificate.
Can a liquid be solid-like?
Yes, densely packed droplets can create high apparent viscosity or yield stress. Check: the liquids remain largely liquid.
Parent correction
‘The oil has turned to water’ is wrong. Correction: it remains as droplets in a water-rich continuous phase.
Final transfer
A plant-based creamy dressing contains tiny stable oil droplets. Is an emulsion plausible? Yes, but identify actual phases and emulsifiers before concluding.
74. A final comparison between chemistry and product design
The science of mayonnaise illustrates a general engineering decision: two ingredients that naturally separate can be reorganised into a useful product when appropriate interfacial molecules, mixing methods and proportions work together. The result is not simply a new substance with a creamy name; it is a structured mixture whose properties emerge from many microscopic droplets.
Ask a child to describe what would happen if the emulsifier was absent while everything else remained comparable. A correct conditional answer says droplets could merge more readily, eventually causing separation. Then ask what the colour of the mixture would prove. It can reveal appearance, but not the exact ingredient identity, safety or long-term stability without further evidence.