Select a solvent and filter an insoluble residue
Use supplied solubility information to separate a solid mixture, track residue and filtrate, and explain why dissolved solute passes through a filter.
Core and Extended · Chemistry 0620, 2026–2028. These paper-based method exercises support supervised laboratory learning; they do not certify practical competence.
Before you begin
- Define solute, solvent, residue and filtrate.
- Distinguish dissolved solute from suspended solid particles.
Work on paper. Try each question before revealing help, and explain why your method works.
Quick readiness check
Which property enables the supplied water-based salt/sand separation?
What you will learn
- Explain selective dissolution and filtration.
- Choose the method from supplied properties and follow substances through the stages.
Choose a solvent that separates the stated components
A suitable solvent can dissolve one solid in a mixture while leaving another undissolved. In a supplied salt/sand model, water dissolves the salt but not the sand. This gives salt solution plus suspended sand, rather than magically removing either substance. If both solids dissolve in the selected solvent, this particular dissolution-plus-filtration route will not separate them into the intended fractions.
Specify the properties and target: are you trying to recover the insoluble solid, the dissolved solid, the solvent, or more than one component? The next stage depends on that target. A solvent should be appropriate to the substances and supervised method; a familiar name alone does not prove selective solubility for every mixture. The paper examples use supplied assumptions rather than instructions to improvise chemical experiments.
A filter separates suitable undissolved particles
Filter paper in a supported funnel retains the undissolved solid residue while the liquid passes into a receiver as filtrate. For the salt/sand model, sand is the residue and salt solution is the filtrate. Dissolved salt travels with the solvent through the filter; filtration is not a way to remove that dissolved salt from water.
If the target is dry sand, an appropriate supervised wash can remove adhering solution before drying. If the target is salt, a later crystallisation stage is needed; if the target is water, distillation and condensation can collect it. Avoid saying clear filtrate equals pure solvent, and do not combine both recovered fractions again if the purpose is separation.
Pause and explain
A mixture's two solids both dissolve in a chosen solvent. Will this filtration route recover one as an insoluble residue?
Worked example
A supplied mixture contains 8.0 g sand and 12.0 g salt. Enough water dissolves all the salt but none of the sand. Track both materials through filtration under an ideal no-loss model.
Show the worked solution
- Water selectively dissolves the 12.0 g salt.
- The 8.0 g undissolved sand remains as filtration residue.
- The filtrate contains the dissolved salt and solvent; the ideal model has separated fractions but not yet dry recovered salt.
Answer Residue: 8.0 g sand. Filtrate: water with 12.0 g dissolved salt under the ideal no-loss assumptions.
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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.
Describe how the supplied salt/sand mixture becomes residue and filtrate using water.
Give me a hint
Use the stated selective solubilities before the filter stage.
Compare my reasoning
- Water dissolves salt while sand remains undissolved.
- A supported filter retains sand as residue.
- Salt solution passes through as filtrate, ready for a later appropriate recovery stage.
Dissolve salt selectively, filter sand as residue, collect salt solution as filtrate.
Look for these in your work
- The solubility reason precedes filtration.
- Both output fractions are identified.
A filter collects 7.6 g dry sand from the ideal 8.0 g starting sand example. Calculate the recovery percentage and give a possible reason it is not 100%.
Give me a hint
Compare recovered target mass with its initial mass, not the whole mixture mass.
Compare my reasoning
- Use the target sand mass: 7.6/8.0×100.
- The recovery is 95%.
- Some sand may remain on transfer apparatus or be lost during handling; the mass result alone does not prove which cause occurred.
95% sand recovery; handling or transfer loss is a possible explanation, not a proven cause from mass alone.
Look for these in your work
- The target component sets the denominator.
- The proposed cause is distinguished from a measured fact.
A hypothetical powder contains two solids both soluble in water, but one soluble and one insoluble in another suitable solvent supplied by a supervised method. Compare the dissolution/filtration choices.
Give me a hint
Ask which solvent creates different retained and passing fractions.
Compare my reasoning
- Water puts both solids into the filtrate, so that route does not separate them as intended.
- The supplied selective solvent dissolves one while leaving the other undissolved.
- Filtration can then separate the retained solid from the dissolved component, followed by a suitable recovery stage.
Use the supplied selective solvent for this route; water followed by filtration alone does not separate the two dissolved solids.
Look for these in your work
- Both sets of solubility information are applied.
- Separation and later recovery are distinguished.
Common mistakes
- Calling filtration a separation of every dissolved solute from solvent.
- Choosing a solvent without checking both components' solubilities.
- Equating transparent filtrate with a pure solvent.
- Claiming an ideal no-loss calculation guarantees a real recovery yield.
What can you explain now?
Where is the dissolved salt after filtering the stated salt/sand/water model?
Compare with the explanation
In the filtrate.
Only the suitable undissolved sand particles are retained as residue.
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Make it stick
Explain why filtration works for the supplied salt/sand model and fails when both target solids dissolve in the chosen solvent.
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.