Secondary 2 Chemistry Tutor Hougang: a muddy-water sample is left on a table. Some particles gradually settle at the bottom, leaving clearer liquid above. The settling is sedimentation. Carefully pouring off that upper liquid without disturbing the settled material is decantation. Passing a liquid through an appropriate porous medium to retain suspended particles is filtration. These are three related but different processes. If a child can say what each achieves and what remains, a difficult separation-techniques question becomes much easier.
Parents searching for Secondary 2 Science tuition in Hougang, decantation notes, sedimentation versus filtration or how to separate mud from water often notice that students know the word “filter” but cannot decide whether a particular mixture first needs settling. The correct choice depends on the nature of the particles, the goal of the separation, and the quality of the final liquid needed.
I teach separation methods by tracing the matter from start to finish. Where did the solid go? Where is the liquid? Does the apparently clear top layer still contain dissolved material or very fine particles? And was any chemical reaction needed? Asking these questions turns a list of apparatus names into a scientific explanation that can transfer to many mixtures.
Sections: the three processes · worked mixtures · common mistakes · practice questions with answers · parent and tutor advice. The broader method-selection guide is Filtration, Evaporation or Distillation?.
1. Sedimentation: allow particles to settle
Sedimentation occurs when suspended particles settle through a fluid under an influence such as gravity. In a familiar school example, sufficiently large or dense sand or soil particles may settle to the bottom of a vessel of still water. A layer of sediment forms, and an upper liquid layer becomes clearer as particles leave suspension. This process uses a physical difference between the dispersed particles and their surrounding fluid.
Do not teach “all heavy particles always sink quickly” as an absolute rule. Particle size, shape, density relative to the liquid, liquid viscosity and agitation can affect settling behaviour. Very fine particles may settle only slowly or remain suspended for a long time. A solid dissolving into the liquid behaves differently from suspended grains.
The correct school-level statement is that the particular insoluble particles in the stated mixture are able to settle under the given conditions. We should not infer that an apparently clear top layer is free of every dissolved substance, microorganism or very fine suspended particle.
2. Decantation: move the upper liquid carefully
After sedimentation has created a sufficiently distinct lower sediment layer and an upper liquid layer, decantation transfers the upper liquid without intentionally transferring the settled solids. In a diagram, that usually means carefully tilting the container and pouring off the top liquid into another receiving container while leaving most sediment behind.
The method can be useful as a preliminary separation, but it is not automatically complete purification. If the liquid is poured too quickly, sediment may be disturbed and carried over. Fine suspended particles may remain in the poured liquid even after some larger ones have settled. The decanted liquid is not necessarily chemically pure or safe to drink.
A teacher may demonstrate a glass rod or other suitable technique to guide the pouring. At home, students can practise reading labelled diagrams rather than handling unknown water samples or glass apparatus. The intellectual skill is distinguishing which layer moves and which substance remains.
3. Filtration: pass a liquid through a retaining medium
Filtration uses an appropriate porous medium, often filter paper in school Science, to retain suspended insoluble particles while allowing the liquid through. The retained solid is the residue. The liquid collected after passing through the filter is the filtrate. These terms have specific meanings that should not be confused with the paper or receiving beaker.
If sand is suspended in water and the filter retains it, the sand is residue and the passing water is filtrate. But if dissolved sodium chloride was present in that water, the filtrate can still be salt solution. The filtration does not ordinarily remove dissolved salt ions merely because the receiving liquid looks clear.
The word “filter” also does not guarantee that every tiny particle or microorganism is removed. Different filtering media have different characteristics. A school filter-paper exercise is an introductory model, not a certification of potable water.
| Method | What happens | What it cannot guarantee |
|---|---|---|
| Sedimentation | Settle suitable suspended particles | All particles settle completely |
| Decantation | Transfer upper liquid from a separated layer | Upper liquid contains no contamination |
| Filtration | Retain suitable insoluble particles while liquid passes | Dissolved solutes or all microbes are removed |
| Distillation | Vaporise and condense a suitable volatile component | Every impurity is removed in every apparatus |
4. Sedimentation and decantation are not synonyms
A student might write “decantation is when sand sinks”. That describes the settling process rather than the subsequent transfer of liquid. Another might label the clear upper liquid “sedimentation”; that confuses a region of the diagram with the process. Ask the learner to describe what moves, when it moves and why.
I give the child a two-frame diagram. Frame one shows particles slowly collecting at the bottom while the vessel stays still. Frame two shows the container tilted to pour off the upper liquid. The first is sedimentation. The second is decantation. The events can form a sequence, but they are not the same action.
5. The meaning of sediment and supernatant
The sediment is the material that has settled at the bottom. The supernatant is the fluid layer above it. These terms describe the material’s location or state after settling. The process of transferring the supernatant is decantation. A school may use simpler language such as “clear liquid above the solid”; students should follow the vocabulary appropriate to their taught course.
It is helpful to name the components in full. In a sand-and-water example, the sediment consists largely of sand, and the supernatant consists of water with whatever dissolved or fine suspended material may remain. The upper liquid being relatively clear is not proof of complete purity.
6. Why leaving a mixture still can matter
A mixture that is continuously stirred may keep particles suspended instead of allowing them to settle. In the simple gravitational settling model, leaving a container undisturbed permits settling to occur. Vibration, flow or repeated stirring can make a clear interface harder to develop. The appropriate duration depends on the mixture, particle properties and the separation objective.
A pupil who says “the sand cannot sink if the water is cloudy” has mistaken appearance for a physical restriction. The water may look cloudy during settling because some particles remain suspended, while larger particles have already reached the bottom. We can describe the partial result without claiming the entire process is finished.
7. Why clearer water is not necessarily clean water
Muddy water can become less visibly cloudy after settling or filtering, but dissolved salts, dissolved chemicals and microorganisms may remain. Each method changes a particular property of the mixture. For drinking-water safety, treatment requires processes and monitoring appropriate to the hazards, and visual clarity alone is inadequate.
This distinction is useful for Singapore students thinking about water supply and sustainable cities. Water treatment is a multi-stage engineering task, not simply a choice between “dirty” and “clear” in a photograph. If a science question concerns dissolved sodium chloride, an ordinary sand filter or decantation cannot be assumed to remove it.
The water-treatment overview is covered in Water Treatment, NEWater and Desalination Explained. This page stays with the smaller decisions about sedimentation, decantation and filtration.
8. Worked example: a beaker of sand and water
Research task: A student is given a mixture of sand and water and wants to separate the visible sand. One acceptable conceptual route is to let the sand settle, then carefully decant much of the upper water. If a clearer liquid is required, use an appropriate filtration step. The exact procedure depends on the question’s aim, equipment and desired degree of separation.
If the student is asked what is left at the bottom after settling, name the sand sediment. If asked what is poured away, name the upper liquid. If asked what passes through filter paper, name the filtrate. The diagram-reading vocabulary must match the stage being shown.
A strong answer gives a reason: particles of sand are insoluble under the stated conditions, and their settling and retention can be used to separate them physically. No chemical reaction is needed. That is why the method can work even if the sand and water remain chemically unchanged.
9. Worked example: salt water that looks clear
Suppose the sample contains only dissolved salt in water. Waiting for sedimentation will not normally cause the dissolved ions to settle as visible grains under ordinary classroom conditions. Carefully pouring the liquid into another cup will not separate salt from water. An ordinary school filter also allows the salt solution to pass.
If the objective is to recover suitable solid salt, consider an appropriate evaporation or crystallisation method. If the objective is to collect the water, simple distillation may be appropriate. The important correction is not “wait longer” but “the solute is dissolved, so this separation principle is unsuitable”.
See Separating Salt and Sand for the complete sequence involving both insoluble and soluble solids.
10. Worked example: coloured water after filtering
A dark dye is dissolved in water. The student passes it through ordinary filter paper and is surprised to collect similarly coloured filtrate. The colour was created by dissolved dye particles that can travel with the liquid. The method removes suitable suspended solids, not every dissolved coloured substance.
The child should say precisely what they observed rather than conclude that the filter was broken. A solid filter medium can work correctly for sand while being inappropriate for dissolved dye. Choose the separation technique according to the material’s physical properties.
11. Worked example: thick muddy water after one minute
A mixture with both large sand grains and very fine clay particles may develop a lower sediment while remaining visibly cloudy above it. The partly clarified liquid can still contain fine suspended material. A single photograph after one minute does not establish the eventual settling pattern, and a time estimate cannot be invented without knowing the particles and conditions.
The correct written answer is conditional: some larger particles may have settled, but further settling or an appropriate separation step may be needed. Avoid claiming that the upper layer is pure or that every particle will eventually settle at the same rate.
12. Why pouring too fast changes the result
Decantation depends on avoiding substantial disturbance of the sediment. If the container is shaken or poured abruptly, settled particles can be carried into the receiving vessel. The result is less clear, not necessarily because the substance chemically changed, but because the physical separation was incomplete.
When asked for an improvement, specify controlled gentle transfer of the upper liquid while leaving the sediment behind. If a more thorough removal of suspended particles is required, add an appropriately selected filtration step. The improvement must address the actual source of contamination.
13. Why filtration may still follow decantation
Decantation often removes much of the liquid from a settled bulk solid, but some suspended particles may remain. Filtration can then improve removal of certain particles, depending on filter characteristics. The sequence may also reduce the amount of bulky sediment passing into the filter, although the exact advantage depends on the system.
This is an example of process design: different methods can be combined because each has different strengths. A student who writes every separation method in a random order has not yet learned which property each one uses. A well-designed sequence accounts for the mixture after each stage.
14. Separating two immiscible liquids is a different decantation problem
The term decantation can also describe carefully separating layers of liquids that do not mix appreciably, such as oil and water under suitable conditions. These form layers because of their physical behaviour and densities, although real emulsions can complicate the situation. Pouring off a layer can sometimes work, but a separating funnel may give better control in an appropriate supervised laboratory.
Do not assume that a simple filter paper will separate two immiscible liquids. Both liquid phases may pass or wet the filter in ways that defeat the intended result. Nor should students confuse a separating funnel with a filter funnel: they are different pieces of apparatus operating on different principles.
15. Why oil and water layers do not make a salt solution
Ordinary cooking oil and water are largely immiscible, so after adequate time they can form separate layers. Salt dissolves in water in a different way; the dissolved ions are distributed within the aqueous phase and do not normally form a separate floating or sinking layer of dry salt. These material differences determine which separation technique might work.
Students often use the word ‘separate’ for every mixture without asking what form the components take. A complete explanation distinguishes two immiscible liquid phases, a suspended solid in a liquid, and a dissolved solute. The same word ‘mixture’ can describe all three, but the appropriate method can differ.
16. What particle size changes
Imagine three jars containing sand grains, fine clay and dissolved sodium chloride, respectively. Larger insoluble grains may settle readily. Fine clay can remain suspended for longer. Dissolved ions are not simply tiny sand grains waiting for enough time to fall to the bottom. The particle interactions and state of dispersion differ fundamentally.
Do not assert that every small particle will settle if we wait exactly ten minutes, or that all colloidal dispersions behave identically. The actual distribution, densities, viscosity and interparticle forces can matter. A lower-secondary answer should follow the properties stated in the question, not invent a universal settling time.
17. What density can and cannot tell you
A suspended solid that is denser than a liquid may settle under gravity when other conditions permit, but density alone does not predict the speed or completeness of separation. Particle size and shape affect motion through liquid, while agitation can prevent sediment from collecting. Some materials float or remain suspended due to other factors.
A learner who writes “the heavier particles sink” may be using colloquial weight language imprecisely. If the scientific explanation calls for it, refer to density relative to the fluid and the actual suspended particles. Not everything with greater total mass sinks faster, especially when objects or particles differ greatly in size and form.
18. What is a suspension?
A suspension contains particles dispersed through a fluid that are not dissolved at the molecular or ionic scale. Depending on the particles and system, the mixture may scatter light, look cloudy, and potentially settle or be separated by an appropriate physical method. Muddy water is a familiar school example, though real muddy water may include a range of particle sizes and dissolved components.
A solution differs because its solute is distributed at the molecular or ionic scale. This is why dissolved sugar and salt do not settle in the way sand grains may settle. If the child thinks dissolved sugar is simply microscopic sediment, return to the particle model rather than assign another list of separation techniques.
19. Is a suspension the same as a colloid?
Not exactly. Colloidal systems contain dispersed particles or structures with characteristic size ranges and behaviour; many do not settle rapidly under ordinary conditions. Simplified school classifications sometimes contrast a suspension that may settle with a colloid that remains dispersed for longer. Real materials can be complex, so avoid treating one visual sign as a complete chemical analysis.
A colloid may scatter light, but a light-scattering observation alone does not identify every material in the sample or establish drinking-water safety. Such ideas are useful as extension, but a Secondary 2 pupil’s immediate job is to distinguish dissolved solute from undissolved dispersed particles.
20. Why a clear supernatant can still be a solution
Suppose sand settles out of saltwater. The liquid above may become visually clear while retaining dissolved salt. Pouring the supernatant into another beaker moves that salt solution; it does not separate salt ions from water. The apparent success of sedimentation is limited to the particles that settled.
This is one of my favourite diagnostic questions because it exposes whether the child interprets ‘clear’ as ‘pure’. Ask what the liquid contains after the sand settles. If they reply ‘only water’, the misunderstanding is about dissolved substances, not about pouring technique.
21. A full three-component worked problem
A mixture contains sand, water and dissolved sodium chloride. The task is to recover the sand and also collect the salt separately. First, an appropriate physical process can separate the insoluble sand from the liquid, often filtration, possibly after settling and decantation if useful. Then the salt must be recovered from the salt solution using a suitable evaporation or crystallisation procedure.
The important output after the solid–liquid step is sand and salt solution—not sand and pure water. If the final aim instead includes recovering the water itself, a suitable distillation process may be needed. Naming the desired product before choosing the last step is essential.
22. A process map: what remains after each stage
| Stage | Material in the lower or retained fraction | Material in upper or passing fraction |
|---|---|---|
| Initial suspension | Mixed sand and liquid | Mixed sand and liquid |
| Settling | Much of the sand forms sediment | Supernatant water with any remaining dissolved or fine materials |
| Decanting | Sediment largely left behind | Transferred upper liquid, potentially still impure |
| Filtering | Appropriate insoluble particles as residue | Filtrate, which may contain dissolved solute |
| Recovering dissolved salt | Recovered salt if suitable procedure used | Water is removed or collected according to method |
The map shows why we cannot label every collected liquid ‘pure water’. Its contents depend on the starting mixture and the removal properties of each step. A correct diagram traces every substance instead of letting inconvenient components vanish from the drawing.
23. How water treatment uses more than one method
Large-scale treatment of water may involve processes that promote settling, remove suspended particles, and treat microbial or dissolved contaminants through additional methods. Settling basins and filters address different kinds of material, and safe treated water requires suitable quality monitoring. The simple classroom sedimentation model is one conceptual component of a much larger system.
The real-world connection is powerful if kept honest. A student can recognise why preliminary settling might reduce the solids load on later treatment stages without being told that pouring off muddy water makes it safe to drink. The science of clean water is a chain of specific removal tasks and verification.
24. When waiting longer does not solve the problem
If a solution contains only dissolved sodium chloride, waiting longer does not make ordinary salt ions fall out like a layer of sand. Other conditions such as evaporation or changes in solubility can cause solid material to appear, but that is a different physical process. It cannot be explained as ordinary sedimentation of undissolved grains.
If a cloudy suspension contains extremely fine particles, longer settling may or may not clarify it sufficiently within the practical time available. The property and required endpoint matter. ‘Wait until everything settles’ is not a general scientific method for every mixture.
25. Ten mistakes worth fixing precisely
| Mistake | Why it is unreliable | More accurate response |
|---|---|---|
| Calling settling decantation | Decantation is the transfer after separation | Name sedimentation for the settling |
| Calling the upper liquid residue | Residue is the solid retained by a filter | Name supernatant or decanted liquid |
| Calling filter paper the residue | Paper is the medium | Residue is the collected solid |
| Saying decantation removes dissolved salt | Dissolved salt remains in liquid | Choose an appropriate solute-recovery method |
| Clear means potable | Visual clarity is limited evidence | Safety needs suitable testing and treatment |
| All particles settle in ten minutes | Settling depends on mixture properties | Use stated conditions and measurements |
| Filters remove everything | They have specific limitations | Match method to target |
| Oil plus water is a single solution | They are largely immiscible | Recognise the liquid layers |
| All heavy objects sink quickly | Size and fluid behaviour matter | Avoid a universal settling-rate claim |
| Decanting is always more complete than filtering | Methods have different capabilities | Specify the goal and residual contamination |
26. What an exam question is really asking
For ‘describe what happens’, report settling, layer formation or liquid transfer as observed. For ‘explain why’, connect the result to insolubility, physical separation or suitable particle behaviour. For ‘suggest an improvement’, address the actual weakness such as disturbing the sediment or the presence of fine suspended particles. The correct command word keeps the answer focused.
A student who writes ‘because the solution is heavy’ has not supplied an adequate mechanism for most of these questions. Encourage them to name the relevant phase, particle type and physical process. A single precise sentence can be worth more than five vague words about heaviness.
27. How to diagnose a misunderstanding in one minute
Ask, ‘What has settled?’ Then ask, ‘What is still in the clear-looking liquid?’ Finally ask, ‘What would happen if that liquid contained dissolved salt?’ A pupil who answers the first correctly but fails the second needs a solution-versus-suspension explanation, not another lesson on pouring technique.
This is how I prefer to teach a difficult Science topic: identify the first wrong idea. A child who understands sediment but confuses filtrate with residue needs vocabulary practice. One who knows the words but thinks all dissolved substances filter out needs the particle model. More random worksheets cannot replace that diagnosis.
28. Eight changed-case questions that test genuine understanding
Muddy liquid after five minutes
A solid layer has formed but the top is still cloudy. This shows partial settling, not proof that every suspended particle has separated. More settling or appropriate filtration may be needed. Ask which material moved, which remained and what the method still cannot establish. A strong response changes when the material or goal changes.
Clear salt solution
There is no visible sediment. Decanting the liquid cannot separate dissolved salt. Choosing a solute-recovery technique depends on whether the goal is to collect water or salt. Ask which material moved, which remained and what the method still cannot establish. A strong response changes when the material or goal changes.
Two separate liquid layers
Oil and water can separate into immiscible layers. Distinguish this from sand sedimentation and consider controlled liquid-layer separation rather than ordinary filter paper. Ask which material moved, which remained and what the method still cannot establish. A strong response changes when the material or goal changes.
Pouring too fast
The sediment is stirred up and carried into the new vessel. The method should minimise disturbance and leave most settled material behind. Ask which material moved, which remained and what the method still cannot establish. A strong response changes when the material or goal changes.
Cloudy filtrate
The liquid passing through the filter still contains particles or other sources of cloudiness. Consider unsuitable filter properties, damage or incomplete separation instead of assuming the experiment failed chemically. Ask which material moved, which remained and what the method still cannot establish. A strong response changes when the material or goal changes.
Sand and dissolved food dye
An appropriate filter may retain sand but allow dissolved dye to pass. The colour of the collected filtrate is not evidence that the filter retained the dye. Ask which material moved, which remained and what the method still cannot establish. A strong response changes when the material or goal changes.
Water after a settling tank
A clearer appearance does not guarantee removal of dissolved contaminants or microorganisms. The observation supports limited suspended-solid separation, not drinking-water safety. Ask which material moved, which remained and what the method still cannot establish. A strong response changes when the material or goal changes.
A floating solid
A particle floating at the surface does not fit the same bottom-settling model. First inspect the material and phases before choosing a physical separation method. Ask which material moved, which remained and what the method still cannot establish. A strong response changes when the material or goal changes.
29. Fourteen original Secondary 2 Science questions
- 1. What is sedimentation?
- 2. What is decantation?
- 3. What is the sediment in a sand–water mixture?
- 4. What is supernatant liquid?
- 5. Why is gentle pouring important?
- 6. What is the residue in a sand-filtration experiment?
- 7. What is the filtrate?
- 8. Does a clear filtrate guarantee the absence of dissolved salt?
- 9. Will dissolved sugar normally form grains at the bottom simply by standing?
- 10. Why might fine clay still be suspended after sand settles?
- 11. Does settled muddy water become automatically safe to drink?
- 12. Does ordinary filter paper necessarily separate oil and water?
- 13. What distinguishes a separating funnel from a filter funnel?
- 14. What additional process is needed to recover suitable solid salt from salt solution?
Answers and explanations
1. The settling of suitable suspended particles under gravity. 2. Transferring an upper liquid layer while leaving most sediment or another separated layer behind. 3. The settled sand. 4. The fluid above a settled layer. 5. Fast pouring can disturb the sediment and carry it into the receiving vessel. 6. The retained sand. 7. The liquid that passes through the filter, which can still contain dissolved solutes. 8. No. 9. No, because sugar is dispersed at the molecular scale in solution. 10. Very fine particles may settle differently or more slowly. 11. No. 12. No; the filter’s action is not automatically suitable for immiscible liquids. 13. The separating funnel controls the removal of liquid layers while a filter funnel supports a porous filtering medium. 14. Suitable evaporation or crystallisation, selected for the target substance and conditions.
These questions are intentionally short, but the tutor should insist on a scientific reason where appropriate. A student who selects filtration correctly for sand yet wrongly uses it to remove dissolved salt needs a particle-model repair, not endless repetition of the word ‘filter’.
30. A seven-day revision rhythm
| Day | Focus | Independent success |
|---|---|---|
| 1 | Suspended sand before and after settling | Labels sediment and upper liquid |
| 2 | A decantation diagram | Tracks transferred liquid |
| 3 | Filtration vocabulary | Labels residue and filtrate |
| 4 | A clear salt solution | Rejects settling as solute recovery |
| 5 | A cloudy filtrate | Explains incomplete separation |
| 6 | A mixture containing sand and salt | Selects sequential methods |
| 7 | A changed situation with no notes | Explains the method and limitation |
The schedule is a suggestion, not a requirement for additional daily tuition. If the child can already explain the next unfamiliar case accurately, use the available study time for other subjects. A short retrieval attempt after a delay can be more revealing than a long copied worksheet.
31. A small-group lesson that reveals different misconceptions
I would give three pupils different mixtures: ordinary sand in water, dissolved sodium chloride in water, and sand together with salt water. Each names the components and draws where the materials will be after a specified separation step. Only then should the group compare its answers. One pupil may confuse sedimentation and decantation, another may assume all solutes can be filtered, while another may lose track of the salt in a multi-step method.
The tutor’s task is to identify and repair each first wrong move. The final check should be another, different question completed independently. A fluent group discussion can be useful, but it is not proof that each pupil has learned the method.
32. What changes between G1, G2 and G3 Science
Singapore’s lower-secondary G1, G2 and G3 Science programmes have different formal expectations. Introductory work may focus on the visible processes of settling, pouring and filtering. More demanding work may ask learners to explain which particles remain, evaluate method limitations and design a sequence of techniques. The school’s taught syllabus and assessment scope are the correct starting points.
The subject level should shape the explanation’s complexity, not whether the student deserves clear scientific reasoning. A simpler task can still be solved with great care. An advanced term should only be added if it explains something the learner is ready to understand.
33. What Hougang parents should ask a Science tutor
Bring a recent marked Science question, the current topic list and the child’s G-level. Ask the tutor to identify whether the pupil confuses the order of processes, the location of sediment, the meaning of residue and filtrate, or the behaviour of dissolved material. The next lesson should address that precise gap and check a changed case rather than assign a generic extra worksheet.
If comparing Secondary 2 Chemistry tuition in Hougang or near Kovan, verify the actual teaching venue, suitable subject level, timetable, fees and availability. A place name in an article title does not prove that a classroom currently operates there. The eduKate small-group Mathematics reference illustrates individual correction but is not confirmation of a Hougang Chemistry timetable.
34. Frequently asked questions
Are sedimentation and decantation the same?
No. One is settling; the other is transferring a layer after separation.
What is the supernatant?
The fluid above sediment.
What is residue?
The retained solid on a filter, not the filter paper.
What is filtrate?
The liquid passing through the filter.
Can decanting remove dissolved salt?
No, not by ordinary transfer of salt solution.
Why may muddy water remain cloudy?
Some fine particles can stay suspended after larger particles settle.
Is clear water necessarily pure?
No. Dissolved material and microorganisms may remain.
Why pour carefully?
To reduce disturbance and transfer of sediment.
Can filtration follow decantation?
Yes, if additional suitable suspended solids need removal.
Is a separating funnel a filtering funnel?
No. The apparatus and physical principles differ.
Can all suspensions settle quickly?
No. Settling depends on material properties and conditions.
What is the safest home practice?
Use labelled diagrams and written evidence questions rather than experimenting with unknown samples.
35. Follow the connected Chemistry learning route
For the general method choice, read Filtration, Evaporation or Distillation?. For sand and salt together, use Separating Salt and Sand. To see why a dissolved solute is different from a suspended solid, use Solute, Solvent and Solution. For experimental design, see Control Experiments and Comparison Samples.
Official syllabus context: G1 Lower Secondary Science and G2/G3 Lower Secondary Science. Educator references include Alloprof separation techniques and Sydney Water stage-four Science. See the Hougang Chemistry reference library for later study.
The explanation I want the pupil to own
“The sand settled, then the upper liquid was poured off without disturbing most of it. That liquid might still contain dissolved substances or fine particles, so it is not necessarily pure water.” A learner who can explain those words and select a different method when the mixture changes has begun to understand separation science.