Order immiscible liquids by density
Predict which liquid forms the upper layer only after confirming that the liquids do not mix.
Section 1.4 · Density
Extended only (Supplement); Physics 0625, 2026–2028, section 1.4. Predict the order of liquids from density only when they do not mix. Use the supplied densities under the stated conditions; do not infer stable separate layers for miscible liquids. Written practice is self-checked; supervised practical experience, cumulative assessment and human subject-teacher review remain pending.
Before you begin
- Compare values in a common density unit.
- Distinguish mixing from separate liquid layers.
Work on paper. Try each question before revealing help, and explain why your method works.
Quick readiness check
What condition allows the separate-layer density rule here?
What you will learn
- Predict layer order for non-mixing liquids.
- Explain why density values alone do not establish layers for miscible liquids.
The less dense liquid settles above
When two liquids do not mix and are allowed to settle, the less dense liquid lies above the denser liquid in the simple model. Original illustrative liquids A, B and C with densities 0.80,1.00,1.20 g/cm³ and explicitly stated mutual immiscibility arrange from top to bottom as A, B, C.
The ordering follows density, not the total mass poured or the order in which the liquids were added. A larger amount of A can still form the upper layer; its quantity changes layer depth, not the material density under unchanged conditions. The diagram is schematic and does not claim a measured layer thickness.
Check the non-mixing condition
Two liquids of different densities do not necessarily form stable separate layers. If they are miscible, they can mix into a solution. The syllabus's layer prediction explicitly assumes they do not mix. Do not apply a density-order rule while ignoring that condition.
If densities are written in different units, convert first. A value 900 kg/m³ equals 0.90 g/cm³ and is less than 1.10 g/cm³. Label each liquid and state top-to-bottom order explicitly; a list of numbers alone can leave the physical arrangement unclear.
Pause and explain
A = 0.80, B = 1.00 and C = 1.20 g/cm³ do not mix. Which is the top-to-bottom order?
Worked example
Three mutually non-mixing liquids have A = 0.80, B = 1.00 and C = 1.20 g/cm³. Give their settled order.
Show the worked solution
- Compare densities in the same units.
- The least dense liquid A is uppermost.
- The order from top to bottom is A, B, C.
Answer Top to bottom: A, B, C.
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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.
Order mutually non-mixing liquids A = 0.80, B = 1.00, C = 1.20 g/cm³ from top to bottom.
Give me a hint
The least dense layer settles above the others.
Compare my reasoning
- A has the smallest density.
- B is intermediate and C greatest.
- Top-to-bottom order is A, B, C.
A, B, C.
Look for these in your work
- State the order direction.
- Use the non-mixing condition.
Non-mixing liquids A,B,C have densities 0.85,1.10,0.95 g/cm³. State their top-to-bottom order.
Give me a hint
Sort the density values in increasing order.
Compare my reasoning
- A at 0.85 is least dense.
- C at 0.95 is intermediate.
- B at 1.10 lies below both.
A, C, B.
Look for these in your work
- Compare all three values.
- Keep each label paired with its density.
Two explicitly miscible liquids have densities 0.90 and 1.10 g/cm³. Can you claim the first remains as a separate upper layer after mixing?
Give me a hint
Check whether the premise for separate layers is satisfied.
Compare my reasoning
- Their densities differ.
- But the problem states that they mix.
- Stable separate layers cannot be justified using this immiscible-liquid rule.
No; the non-mixing condition is not satisfied.
Look for these in your work
- Identify miscibility.
- Avoid an unsupported layer prediction.
Common mistakes
- The liquids must not mix.
- Compare density rather than total poured mass.
- Convert units before ordering.
What can you explain now?
Non-mixing liquids have densities 900 kg/m³ and 1.10 g/cm³. Which lies above?
Compare with the explanation
The 900 kg/m³ liquid.
It is 0.90 g/cm³, less than 1.10 g/cm³.
After trying it yourself, choose your next review. This is your self-assessment.
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Make it stick
Give a labelled layer prediction, then state why the same claim fails when the liquids mix.
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.