Solution vocabulary and saturation at a stated temperature
Distinguish solvent, solute, solution, saturation, residue and filtrate using a mixture model and a temperature-dependent solubility calculation.
Exam scope and assessment notes
Core and Extended · Chemistry 0971, 2026–2028. These paper-based method exercises support supervised laboratory learning; they do not certify practical competence. Cambridge states that IGCSE 0971 has the same subject content as IGCSE 0620, with 9–1 grading. This StudyForA pathway maps the 2026–2028 syllabus only. This 9–1 graded qualification is available only in a limited number of administrative zones. Confirm that your centre can enter you for this code and exam series with Cambridge International. Cambridge has published a separate syllabus for 2029. StudyForA has not reconciled that version yet; this page supports exams in 2026, 2027 and 2028 only.
Before you begin
- Distinguish a soluble substance from an insoluble solid.
- Use a ratio to scale a supplied amount.
Work on paper. Try each question before revealing help, and explain why your method works.
Quick readiness check
In salt water, which is the solvent?
What you will learn
- Describe the six required solution and separation terms.
- Use supplied solubility data without confusing dissolved solute, insoluble residue and filtrate.
Dissolving does not destroy the solute
A solvent is the substance that dissolves a solute; the solute is the substance being dissolved. The resulting solution contains one or more dissolved solutes mixed with the solvent. In salt water, water is the solvent and dissolved salt is the solute. A solution is not necessarily pure solvent, and a transparent liquid is not automatically pure water.
A saturated solution contains the maximum concentration of that solute that can be dissolved at the specified temperature. The temperature qualification matters because solubility can change with temperature. Saturated is different from a vague concentrated label. Supplied solubility data describe a particular solute, solvent and temperature; do not assume every solid becomes more soluble by the same amount on heating.
Follow substances through a separation
A residue is material left after a separation process such as filtration, evaporation or distillation. In filtering a sand/salt/water model, undissolved sand remains as the residue on the filter. The filtrate is the liquid or solution that has passed through the filter; it can contain dissolved salt. Filter paper separates suspended solid particles, rather than removing all dissolved solute.
A later evaporation can leave dissolved salt as an evaporation residue while the solvent leaves as vapour. If the purpose is to collect that solvent, distillation and condensation are needed instead. The same word residue can describe material remaining at different stages, so identify the process and substance rather than assuming residue always means sand or waste.
Pause and explain
Why must saturation be stated at a specified temperature?
Worked example
At 20°C a hypothetical salt dissolves up to 36 g per 100 g water. Add 25 g salt to 50 g water at that temperature and mix to equilibrium. Calculate dissolved salt and excess solid.
Show the worked solution
- Scale the supplied limit: 36×50/100=18 g can dissolve.
- The 25 g addition exceeds that capacity by 25−18=7 g.
- The solution is saturated at 20°C and 7 g solid remains under the stated model assumptions.
Answer 18 g dissolved and 7 g excess solid; the solution is saturated at 20°C.
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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.
Define solvent, solute and solution for a salt-water model.
Give me a hint
Identify which substance dissolves and which is dissolved.
Compare my reasoning
- Water is the solvent, the substance dissolving the salt.
- Salt is the solute, the substance being dissolved.
- Salt water is the solution containing the dissolved solute mixed with the solvent.
Water: solvent; salt: solute; salt water: solution.
Look for these in your work
- The dissolving roles are correctly assigned.
- The solution is described as a mixture rather than pure water.
Filter a supplied sand/salt/water mixture after the salt has completely dissolved. Identify residue and filtrate, then explain what remains after suitable evaporation of the filtrate.
Give me a hint
Track the insoluble solid separately from dissolved salt.
Compare my reasoning
- Sand remains as the filtration residue.
- Salt solution passes through as filtrate.
- Evaporation removes solvent and can leave salt as a new residue; filtration alone did not remove it.
Filtration residue: sand. Filtrate: salt solution. Evaporation residue: salt under the supplied model.
Look for these in your work
- Each term is linked to its own process.
- Dissolved salt is retained in the filtrate until the later separation.
The hypothetical solubility is 36 g per 100 g water at 20°C and 50 g per 100 g water at 60°C. A hot saturated solution contains 20 g water, with no solvent lost on cooling. Predict the mass of crystals at 20°C.
Give me a hint
Find the hot and cool dissolved capacities for the same water mass.
Compare my reasoning
- At 60°C the dissolved salt is 50×20/100=10 g.
- At 20°C only 36×20/100=7.2 g can remain dissolved at equilibrium.
- The predicted crystallised mass is 10−7.2=2.8 g, assuming no solvent loss and the stated solubility model.
2.8 g crystals at 20°C under the supplied equilibrium/no-solvent-loss assumptions.
Look for these in your work
- Both temperature-specific capacities are scaled correctly.
- The prediction is limited to the stated model conditions.
Common mistakes
- Calling a clear filtrate proof of pure water.
- Using saturated without the specified temperature or solubility information.
- Expecting filter paper to remove a dissolved salt.
- Treating residue as one fixed substance regardless of the process.
What can you explain now?
Does salt-water filtrate contain only solvent?
Compare with the explanation
No, it can still contain dissolved salt.
A filter removes suitable undissolved particles, not all dissolved solute.
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Make it stick
Define all six terms and explain why a filtered clear solution can still contain a solute and form a residue later.
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.