Start here
This learner’s guide solves one precise problem: separating solution volume from concentration. The controlling question is: Are both the volume and the concentration equal, or has only one variable been matched? A reliable answer comes from a repeatable chain of evidence, not from the first familiar word, number or shape that catches your eye.
The portable rule is: The amount of dissolved substance depends on both solution volume and concentration; equal volumes contain equal amounts only when concentration is also equal. You will study the mechanism, inspect worked cases, repair common misconceptions, complete graded independent practice, revisit the idea after a delay and learn an examination routine that remains usable under time pressure.
Use the complete Learner’s Guide volume directory as the route through this series and the original PSLE Learning Guide for the foundation. Visit the Science hub for related subject learning. For current paper-format information, consult the official SEAB PSLE formats examined in 2026.
The mechanism
Mechanism 1
A solution contains a dissolved substance spread through a solvent. Volume tells how much solution is present. Concentration tells how much dissolved substance is present in a given volume. These are related but not interchangeable quantities.
Mechanism 2
For two samples with equal volume, the more concentrated sample contains more dissolved substance. For two samples with equal concentration, the larger-volume sample contains more dissolved substance.
Mechanism 3
Dilution adds solvent without adding dissolved substance. The total amount of dissolved substance stays the same while concentration decreases and solution volume increases, provided none is lost.
Mechanism 4
Evaporation removes solvent. If the dissolved substance does not leave, its amount stays the same while the remaining solution becomes more concentrated. Do not say that evaporation creates more solute.
Mechanism 5
A fair comparison identifies what was kept the same, what changed and what was measured. Colour intensity can be evidence only when the same substance, container, lighting and observation method make the comparison valid.
A strong explanation makes its evidence visible. First identify the information that matters. Next state the relationship between those pieces. Then apply the relationship to the exact case. Finally check the conclusion against the whole sentence, data set, experimental condition or diagram. This four-move structure prevents a correct-looking answer from resting on a wrong reason.
Worked case laboratory
Case 1: Sample A and Sample B each contain 50 mL of the same solution type. A has concentration 1 units per 100 mL and B has 5 units per 100 mL. Compare the dissolved amount.
Answer: B contains more The volumes are equal, so concentration decides the comparison. The sample with concentration 5 contains more dissolved substance in the same volume. Equal volume alone would not justify equality. The decision is controlled by The amount of dissolved substance depends on both solution volume and concentration; equal volumes contain equal amounts only when concentration is also equal. A useful self-check is to name one tempting wrong interpretation and explain which piece of evidence rules it out. That extra sentence turns recognition into transferable reasoning.
Case 2: Two samples have the same concentration. One has 100 mL and the other has 150 mL. Which contains more dissolved substance?
Answer: The second sample Concentration is matched, so the larger solution volume contains proportionally more dissolved substance. The comparison uses both variables and does not confuse concentration with total dissolved amount. The decision is controlled by The amount of dissolved substance depends on both solution volume and concentration; equal volumes contain equal amounts only when concentration is also equal. A useful self-check is to name one tempting wrong interpretation and explain which piece of evidence rules it out. That extra sentence turns recognition into transferable reasoning.
Case 3: Water is added to 150 mL of a solution until its volume becomes 250 mL, with no spilling. What changes?
Answer: The dissolved amount stays the same while concentration decreases. Only solvent is added. The same dissolved substance is spread through a larger solution volume, so the amount is conserved but the concentration becomes lower. The decision is controlled by The amount of dissolved substance depends on both solution volume and concentration; equal volumes contain equal amounts only when concentration is also equal. A useful self-check is to name one tempting wrong interpretation and explain which piece of evidence rules it out. That extra sentence turns recognition into transferable reasoning.
Case 4: Some water evaporates from 50 mL of a solution, and the dissolved substance remains in the container. What changes?
Answer: The dissolved amount stays the same while concentration increases. Evaporation removes solvent rather than creating dissolved substance. The unchanged amount is now present in a smaller volume, so the solution becomes more concentrated. The decision is controlled by The amount of dissolved substance depends on both solution volume and concentration; equal volumes contain equal amounts only when concentration is also equal. A useful self-check is to name one tempting wrong interpretation and explain which piece of evidence rules it out. That extra sentence turns recognition into transferable reasoning.
Case 5: Sample A and Sample B each contain 50 mL of the same solution type. A has concentration 5 units per 100 mL and B has 1 units per 100 mL. Compare the dissolved amount.
Answer: A contains more The volumes are equal, so concentration decides the comparison. The sample with concentration 5 contains more dissolved substance in the same volume. Equal volume alone would not justify equality. The decision is controlled by The amount of dissolved substance depends on both solution volume and concentration; equal volumes contain equal amounts only when concentration is also equal. A useful self-check is to name one tempting wrong interpretation and explain which piece of evidence rules it out. That extra sentence turns recognition into transferable reasoning.
Case 6: Two samples have the same concentration. One has 100 mL and the other has 150 mL. Which contains more dissolved substance?
Answer: The second sample Concentration is matched, so the larger solution volume contains proportionally more dissolved substance. The comparison uses both variables and does not confuse concentration with total dissolved amount. The decision is controlled by The amount of dissolved substance depends on both solution volume and concentration; equal volumes contain equal amounts only when concentration is also equal. A useful self-check is to name one tempting wrong interpretation and explain which piece of evidence rules it out. That extra sentence turns recognition into transferable reasoning.
Case 7: Water is added to 150 mL of a solution until its volume becomes 250 mL, with no spilling. What changes?
Answer: The dissolved amount stays the same while concentration decreases. Only solvent is added. The same dissolved substance is spread through a larger solution volume, so the amount is conserved but the concentration becomes lower. The decision is controlled by The amount of dissolved substance depends on both solution volume and concentration; equal volumes contain equal amounts only when concentration is also equal. A useful self-check is to name one tempting wrong interpretation and explain which piece of evidence rules it out. That extra sentence turns recognition into transferable reasoning.
Case 8: Some water evaporates from 50 mL of a solution, and the dissolved substance remains in the container. What changes?
Answer: The dissolved amount stays the same while concentration increases. Evaporation removes solvent rather than creating dissolved substance. The unchanged amount is now present in a smaller volume, so the solution becomes more concentrated. The decision is controlled by The amount of dissolved substance depends on both solution volume and concentration; equal volumes contain equal amounts only when concentration is also equal. A useful self-check is to name one tempting wrong interpretation and explain which piece of evidence rules it out. That extra sentence turns recognition into transferable reasoning.
Case 9: Sample A and Sample B each contain 50 mL of the same solution type. A has concentration 4 units per 100 mL and B has 2 units per 100 mL. Compare the dissolved amount.
Answer: A contains more The volumes are equal, so concentration decides the comparison. The sample with concentration 4 contains more dissolved substance in the same volume. Equal volume alone would not justify equality. The decision is controlled by The amount of dissolved substance depends on both solution volume and concentration; equal volumes contain equal amounts only when concentration is also equal. A useful self-check is to name one tempting wrong interpretation and explain which piece of evidence rules it out. That extra sentence turns recognition into transferable reasoning.
Case 10: Two samples have the same concentration. One has 100 mL and the other has 150 mL. Which contains more dissolved substance?
Answer: The second sample Concentration is matched, so the larger solution volume contains proportionally more dissolved substance. The comparison uses both variables and does not confuse concentration with total dissolved amount. The decision is controlled by The amount of dissolved substance depends on both solution volume and concentration; equal volumes contain equal amounts only when concentration is also equal. A useful self-check is to name one tempting wrong interpretation and explain which piece of evidence rules it out. That extra sentence turns recognition into transferable reasoning.
Case 11: Water is added to 150 mL of a solution until its volume becomes 250 mL, with no spilling. What changes?
Answer: The dissolved amount stays the same while concentration decreases. Only solvent is added. The same dissolved substance is spread through a larger solution volume, so the amount is conserved but the concentration becomes lower. The decision is controlled by The amount of dissolved substance depends on both solution volume and concentration; equal volumes contain equal amounts only when concentration is also equal. A useful self-check is to name one tempting wrong interpretation and explain which piece of evidence rules it out. That extra sentence turns recognition into transferable reasoning.
Case 12: Some water evaporates from 50 mL of a solution, and the dissolved substance remains in the container. What changes?
Answer: The dissolved amount stays the same while concentration increases. Evaporation removes solvent rather than creating dissolved substance. The unchanged amount is now present in a smaller volume, so the solution becomes more concentrated. The decision is controlled by The amount of dissolved substance depends on both solution volume and concentration; equal volumes contain equal amounts only when concentration is also equal. A useful self-check is to name one tempting wrong interpretation and explain which piece of evidence rules it out. That extra sentence turns recognition into transferable reasoning.
Case 13: Sample A and Sample B each contain 50 mL of the same solution type. A has concentration 3 units per 100 mL and B has 3 units per 100 mL. Compare the dissolved amount.
Answer: equal amounts The volumes are equal, so concentration decides the comparison. Both variables match, so the dissolved amounts match. Equal volume alone would not justify equality. The decision is controlled by The amount of dissolved substance depends on both solution volume and concentration; equal volumes contain equal amounts only when concentration is also equal. A useful self-check is to name one tempting wrong interpretation and explain which piece of evidence rules it out. That extra sentence turns recognition into transferable reasoning.
Case 14: Two samples have the same concentration. One has 100 mL and the other has 150 mL. Which contains more dissolved substance?
Answer: The second sample Concentration is matched, so the larger solution volume contains proportionally more dissolved substance. The comparison uses both variables and does not confuse concentration with total dissolved amount. The decision is controlled by The amount of dissolved substance depends on both solution volume and concentration; equal volumes contain equal amounts only when concentration is also equal. A useful self-check is to name one tempting wrong interpretation and explain which piece of evidence rules it out. That extra sentence turns recognition into transferable reasoning.
Case 15: Water is added to 150 mL of a solution until its volume becomes 250 mL, with no spilling. What changes?
Answer: The dissolved amount stays the same while concentration decreases. Only solvent is added. The same dissolved substance is spread through a larger solution volume, so the amount is conserved but the concentration becomes lower. The decision is controlled by The amount of dissolved substance depends on both solution volume and concentration; equal volumes contain equal amounts only when concentration is also equal. A useful self-check is to name one tempting wrong interpretation and explain which piece of evidence rules it out. That extra sentence turns recognition into transferable reasoning.
Case 16: Some water evaporates from 50 mL of a solution, and the dissolved substance remains in the container. What changes?
Answer: The dissolved amount stays the same while concentration increases. Evaporation removes solvent rather than creating dissolved substance. The unchanged amount is now present in a smaller volume, so the solution becomes more concentrated. The decision is controlled by The amount of dissolved substance depends on both solution volume and concentration; equal volumes contain equal amounts only when concentration is also equal. A useful self-check is to name one tempting wrong interpretation and explain which piece of evidence rules it out. That extra sentence turns recognition into transferable reasoning.
Case 17: Sample A and Sample B each contain 50 mL of the same solution type. A has concentration 2 units per 100 mL and B has 4 units per 100 mL. Compare the dissolved amount.
Answer: B contains more The volumes are equal, so concentration decides the comparison. The sample with concentration 4 contains more dissolved substance in the same volume. Equal volume alone would not justify equality. The decision is controlled by The amount of dissolved substance depends on both solution volume and concentration; equal volumes contain equal amounts only when concentration is also equal. A useful self-check is to name one tempting wrong interpretation and explain which piece of evidence rules it out. That extra sentence turns recognition into transferable reasoning.
Case 18: Two samples have the same concentration. One has 100 mL and the other has 150 mL. Which contains more dissolved substance?
Answer: The second sample Concentration is matched, so the larger solution volume contains proportionally more dissolved substance. The comparison uses both variables and does not confuse concentration with total dissolved amount. The decision is controlled by The amount of dissolved substance depends on both solution volume and concentration; equal volumes contain equal amounts only when concentration is also equal. A useful self-check is to name one tempting wrong interpretation and explain which piece of evidence rules it out. That extra sentence turns recognition into transferable reasoning.
Case 19: Water is added to 150 mL of a solution until its volume becomes 250 mL, with no spilling. What changes?
Answer: The dissolved amount stays the same while concentration decreases. Only solvent is added. The same dissolved substance is spread through a larger solution volume, so the amount is conserved but the concentration becomes lower. The decision is controlled by The amount of dissolved substance depends on both solution volume and concentration; equal volumes contain equal amounts only when concentration is also equal. A useful self-check is to name one tempting wrong interpretation and explain which piece of evidence rules it out. That extra sentence turns recognition into transferable reasoning.
Case 20: Some water evaporates from 50 mL of a solution, and the dissolved substance remains in the container. What changes?
Answer: The dissolved amount stays the same while concentration increases. Evaporation removes solvent rather than creating dissolved substance. The unchanged amount is now present in a smaller volume, so the solution becomes more concentrated. The decision is controlled by The amount of dissolved substance depends on both solution volume and concentration; equal volumes contain equal amounts only when concentration is also equal. A useful self-check is to name one tempting wrong interpretation and explain which piece of evidence rules it out. That extra sentence turns recognition into transferable reasoning.
Case 21: Sample A and Sample B each contain 50 mL of the same solution type. A has concentration 1 units per 100 mL and B has 5 units per 100 mL. Compare the dissolved amount.
Answer: B contains more The volumes are equal, so concentration decides the comparison. The sample with concentration 5 contains more dissolved substance in the same volume. Equal volume alone would not justify equality. The decision is controlled by The amount of dissolved substance depends on both solution volume and concentration; equal volumes contain equal amounts only when concentration is also equal. A useful self-check is to name one tempting wrong interpretation and explain which piece of evidence rules it out. That extra sentence turns recognition into transferable reasoning.
Case 22: Two samples have the same concentration. One has 100 mL and the other has 150 mL. Which contains more dissolved substance?
Answer: The second sample Concentration is matched, so the larger solution volume contains proportionally more dissolved substance. The comparison uses both variables and does not confuse concentration with total dissolved amount. The decision is controlled by The amount of dissolved substance depends on both solution volume and concentration; equal volumes contain equal amounts only when concentration is also equal. A useful self-check is to name one tempting wrong interpretation and explain which piece of evidence rules it out. That extra sentence turns recognition into transferable reasoning.
Case 23: Water is added to 150 mL of a solution until its volume becomes 250 mL, with no spilling. What changes?
Answer: The dissolved amount stays the same while concentration decreases. Only solvent is added. The same dissolved substance is spread through a larger solution volume, so the amount is conserved but the concentration becomes lower. The decision is controlled by The amount of dissolved substance depends on both solution volume and concentration; equal volumes contain equal amounts only when concentration is also equal. A useful self-check is to name one tempting wrong interpretation and explain which piece of evidence rules it out. That extra sentence turns recognition into transferable reasoning.
Case 24: Some water evaporates from 50 mL of a solution, and the dissolved substance remains in the container. What changes?
Answer: The dissolved amount stays the same while concentration increases. Evaporation removes solvent rather than creating dissolved substance. The unchanged amount is now present in a smaller volume, so the solution becomes more concentrated. The decision is controlled by The amount of dissolved substance depends on both solution volume and concentration; equal volumes contain equal amounts only when concentration is also equal. A useful self-check is to name one tempting wrong interpretation and explain which piece of evidence rules it out. That extra sentence turns recognition into transferable reasoning.
Case 25: Sample A and Sample B each contain 50 mL of the same solution type. A has concentration 5 units per 100 mL and B has 1 units per 100 mL. Compare the dissolved amount.
Answer: A contains more The volumes are equal, so concentration decides the comparison. The sample with concentration 5 contains more dissolved substance in the same volume. Equal volume alone would not justify equality. The decision is controlled by The amount of dissolved substance depends on both solution volume and concentration; equal volumes contain equal amounts only when concentration is also equal. A useful self-check is to name one tempting wrong interpretation and explain which piece of evidence rules it out. That extra sentence turns recognition into transferable reasoning.
Case 26: Two samples have the same concentration. One has 100 mL and the other has 150 mL. Which contains more dissolved substance?
Answer: The second sample Concentration is matched, so the larger solution volume contains proportionally more dissolved substance. The comparison uses both variables and does not confuse concentration with total dissolved amount. The decision is controlled by The amount of dissolved substance depends on both solution volume and concentration; equal volumes contain equal amounts only when concentration is also equal. A useful self-check is to name one tempting wrong interpretation and explain which piece of evidence rules it out. That extra sentence turns recognition into transferable reasoning.
Case 27: Water is added to 150 mL of a solution until its volume becomes 250 mL, with no spilling. What changes?
Answer: The dissolved amount stays the same while concentration decreases. Only solvent is added. The same dissolved substance is spread through a larger solution volume, so the amount is conserved but the concentration becomes lower. The decision is controlled by The amount of dissolved substance depends on both solution volume and concentration; equal volumes contain equal amounts only when concentration is also equal. A useful self-check is to name one tempting wrong interpretation and explain which piece of evidence rules it out. That extra sentence turns recognition into transferable reasoning.
Case 28: Some water evaporates from 50 mL of a solution, and the dissolved substance remains in the container. What changes?
Answer: The dissolved amount stays the same while concentration increases. Evaporation removes solvent rather than creating dissolved substance. The unchanged amount is now present in a smaller volume, so the solution becomes more concentrated. The decision is controlled by The amount of dissolved substance depends on both solution volume and concentration; equal volumes contain equal amounts only when concentration is also equal. A useful self-check is to name one tempting wrong interpretation and explain which piece of evidence rules it out. That extra sentence turns recognition into transferable reasoning.
Case 29: Sample A and Sample B each contain 50 mL of the same solution type. A has concentration 4 units per 100 mL and B has 2 units per 100 mL. Compare the dissolved amount.
Answer: A contains more The volumes are equal, so concentration decides the comparison. The sample with concentration 4 contains more dissolved substance in the same volume. Equal volume alone would not justify equality. The decision is controlled by The amount of dissolved substance depends on both solution volume and concentration; equal volumes contain equal amounts only when concentration is also equal. A useful self-check is to name one tempting wrong interpretation and explain which piece of evidence rules it out. That extra sentence turns recognition into transferable reasoning.
Case 30: Two samples have the same concentration. One has 100 mL and the other has 150 mL. Which contains more dissolved substance?
Answer: The second sample Concentration is matched, so the larger solution volume contains proportionally more dissolved substance. The comparison uses both variables and does not confuse concentration with total dissolved amount. The decision is controlled by The amount of dissolved substance depends on both solution volume and concentration; equal volumes contain equal amounts only when concentration is also equal. A useful self-check is to name one tempting wrong interpretation and explain which piece of evidence rules it out. That extra sentence turns recognition into transferable reasoning.
Case 31: Water is added to 150 mL of a solution until its volume becomes 250 mL, with no spilling. What changes?
Answer: The dissolved amount stays the same while concentration decreases. Only solvent is added. The same dissolved substance is spread through a larger solution volume, so the amount is conserved but the concentration becomes lower. The decision is controlled by The amount of dissolved substance depends on both solution volume and concentration; equal volumes contain equal amounts only when concentration is also equal. A useful self-check is to name one tempting wrong interpretation and explain which piece of evidence rules it out. That extra sentence turns recognition into transferable reasoning.
Case 32: Some water evaporates from 50 mL of a solution, and the dissolved substance remains in the container. What changes?
Answer: The dissolved amount stays the same while concentration increases. Evaporation removes solvent rather than creating dissolved substance. The unchanged amount is now present in a smaller volume, so the solution becomes more concentrated. The decision is controlled by The amount of dissolved substance depends on both solution volume and concentration; equal volumes contain equal amounts only when concentration is also equal. A useful self-check is to name one tempting wrong interpretation and explain which piece of evidence rules it out. That extra sentence turns recognition into transferable reasoning.
Case 33: Sample A and Sample B each contain 50 mL of the same solution type. A has concentration 3 units per 100 mL and B has 3 units per 100 mL. Compare the dissolved amount.
Answer: equal amounts The volumes are equal, so concentration decides the comparison. Both variables match, so the dissolved amounts match. Equal volume alone would not justify equality. The decision is controlled by The amount of dissolved substance depends on both solution volume and concentration; equal volumes contain equal amounts only when concentration is also equal. A useful self-check is to name one tempting wrong interpretation and explain which piece of evidence rules it out. That extra sentence turns recognition into transferable reasoning.
Case 34: Two samples have the same concentration. One has 100 mL and the other has 150 mL. Which contains more dissolved substance?
Answer: The second sample Concentration is matched, so the larger solution volume contains proportionally more dissolved substance. The comparison uses both variables and does not confuse concentration with total dissolved amount. The decision is controlled by The amount of dissolved substance depends on both solution volume and concentration; equal volumes contain equal amounts only when concentration is also equal. A useful self-check is to name one tempting wrong interpretation and explain which piece of evidence rules it out. That extra sentence turns recognition into transferable reasoning.
Case 35: Water is added to 150 mL of a solution until its volume becomes 250 mL, with no spilling. What changes?
Answer: The dissolved amount stays the same while concentration decreases. Only solvent is added. The same dissolved substance is spread through a larger solution volume, so the amount is conserved but the concentration becomes lower. The decision is controlled by The amount of dissolved substance depends on both solution volume and concentration; equal volumes contain equal amounts only when concentration is also equal. A useful self-check is to name one tempting wrong interpretation and explain which piece of evidence rules it out. That extra sentence turns recognition into transferable reasoning.
Case 36: Some water evaporates from 50 mL of a solution, and the dissolved substance remains in the container. What changes?
Answer: The dissolved amount stays the same while concentration increases. Evaporation removes solvent rather than creating dissolved substance. The unchanged amount is now present in a smaller volume, so the solution becomes more concentrated. The decision is controlled by The amount of dissolved substance depends on both solution volume and concentration; equal volumes contain equal amounts only when concentration is also equal. A useful self-check is to name one tempting wrong interpretation and explain which piece of evidence rules it out. That extra sentence turns recognition into transferable reasoning.
Case 37: Sample A and Sample B each contain 50 mL of the same solution type. A has concentration 2 units per 100 mL and B has 4 units per 100 mL. Compare the dissolved amount.
Answer: B contains more The volumes are equal, so concentration decides the comparison. The sample with concentration 4 contains more dissolved substance in the same volume. Equal volume alone would not justify equality. The decision is controlled by The amount of dissolved substance depends on both solution volume and concentration; equal volumes contain equal amounts only when concentration is also equal. A useful self-check is to name one tempting wrong interpretation and explain which piece of evidence rules it out. That extra sentence turns recognition into transferable reasoning.
Case 38: Two samples have the same concentration. One has 100 mL and the other has 150 mL. Which contains more dissolved substance?
Answer: The second sample Concentration is matched, so the larger solution volume contains proportionally more dissolved substance. The comparison uses both variables and does not confuse concentration with total dissolved amount. The decision is controlled by The amount of dissolved substance depends on both solution volume and concentration; equal volumes contain equal amounts only when concentration is also equal. A useful self-check is to name one tempting wrong interpretation and explain which piece of evidence rules it out. That extra sentence turns recognition into transferable reasoning.
Case 39: Water is added to 150 mL of a solution until its volume becomes 250 mL, with no spilling. What changes?
Answer: The dissolved amount stays the same while concentration decreases. Only solvent is added. The same dissolved substance is spread through a larger solution volume, so the amount is conserved but the concentration becomes lower. The decision is controlled by The amount of dissolved substance depends on both solution volume and concentration; equal volumes contain equal amounts only when concentration is also equal. A useful self-check is to name one tempting wrong interpretation and explain which piece of evidence rules it out. That extra sentence turns recognition into transferable reasoning.
Case 40: Some water evaporates from 50 mL of a solution, and the dissolved substance remains in the container. What changes?
Answer: The dissolved amount stays the same while concentration increases. Evaporation removes solvent rather than creating dissolved substance. The unchanged amount is now present in a smaller volume, so the solution becomes more concentrated. The decision is controlled by The amount of dissolved substance depends on both solution volume and concentration; equal volumes contain equal amounts only when concentration is also equal. A useful self-check is to name one tempting wrong interpretation and explain which piece of evidence rules it out. That extra sentence turns recognition into transferable reasoning.
Common misconceptions and targeted repair
1. Equal volumes always contain equal dissolved amounts.
Equal amounts follow only when the compared solutions also have equal concentration. Repair the habit by stating the controlling relationship before calculating, spelling or interpreting. Then cite one detail from the actual question that supports the repaired decision.
2. A more concentrated solution must have a larger volume.
Concentration is an amount-per-volume idea. A small sample can be more concentrated than a large sample. Repair the habit by stating the controlling relationship before calculating, spelling or interpreting. Then cite one detail from the actual question that supports the repaired decision.
3. Dilution removes dissolved substance.
Adding solvent lowers concentration but does not remove dissolved substance if there is no loss or reaction. Repair the habit by stating the controlling relationship before calculating, spelling or interpreting. Then cite one detail from the actual question that supports the repaired decision.
4. Evaporation creates more dissolved substance.
Evaporation can increase concentration by removing solvent while the dissolved amount remains unchanged. Repair the habit by stating the controlling relationship before calculating, spelling or interpreting. Then cite one detail from the actual question that supports the repaired decision.
5. A darker colour always proves higher concentration.
Colour is useful only when substance, container, lighting and observation conditions support that inference. Repair the habit by stating the controlling relationship before calculating, spelling or interpreting. Then cite one detail from the actual question that supports the repaired decision.
6. Volume and concentration can be compared separately when finding total amount.
Both variables matter. State which is equal and how the other changes before concluding. Repair the habit by stating the controlling relationship before calculating, spelling or interpreting. Then cite one detail from the actual question that supports the repaired decision.
Graded independent practice with explained answers
1. Sample A and Sample B each contain 50 mL of the same solution type. A has concentration 1 units per 100 mL and B has 5 units per 100 mL. Compare the dissolved amount.
B contains more The volumes are equal, so concentration decides the comparison. The sample with concentration 5 contains more dissolved substance in the same volume. Equal volume alone would not justify equality. For full control, write a short evidence sentence before checking this answer. If your result differs, identify whether the error came from selecting information, applying the relationship, choosing a form, or failing to reread the completed response.
2. Two samples have the same concentration. One has 100 mL and the other has 150 mL. Which contains more dissolved substance?
The second sample Concentration is matched, so the larger solution volume contains proportionally more dissolved substance. The comparison uses both variables and does not confuse concentration with total dissolved amount. For full control, write a short evidence sentence before checking this answer. If your result differs, identify whether the error came from selecting information, applying the relationship, choosing a form, or failing to reread the completed response.
3. Water is added to 150 mL of a solution until its volume becomes 250 mL, with no spilling. What changes?
The dissolved amount stays the same while concentration decreases. Only solvent is added. The same dissolved substance is spread through a larger solution volume, so the amount is conserved but the concentration becomes lower. For full control, write a short evidence sentence before checking this answer. If your result differs, identify whether the error came from selecting information, applying the relationship, choosing a form, or failing to reread the completed response.
4. Some water evaporates from 50 mL of a solution, and the dissolved substance remains in the container. What changes?
The dissolved amount stays the same while concentration increases. Evaporation removes solvent rather than creating dissolved substance. The unchanged amount is now present in a smaller volume, so the solution becomes more concentrated. For full control, write a short evidence sentence before checking this answer. If your result differs, identify whether the error came from selecting information, applying the relationship, choosing a form, or failing to reread the completed response.
5. Sample A and Sample B each contain 50 mL of the same solution type. A has concentration 5 units per 100 mL and B has 1 units per 100 mL. Compare the dissolved amount.
A contains more The volumes are equal, so concentration decides the comparison. The sample with concentration 5 contains more dissolved substance in the same volume. Equal volume alone would not justify equality. For full control, write a short evidence sentence before checking this answer. If your result differs, identify whether the error came from selecting information, applying the relationship, choosing a form, or failing to reread the completed response.
6. Two samples have the same concentration. One has 100 mL and the other has 150 mL. Which contains more dissolved substance?
The second sample Concentration is matched, so the larger solution volume contains proportionally more dissolved substance. The comparison uses both variables and does not confuse concentration with total dissolved amount. For full control, write a short evidence sentence before checking this answer. If your result differs, identify whether the error came from selecting information, applying the relationship, choosing a form, or failing to reread the completed response.
7. Water is added to 150 mL of a solution until its volume becomes 250 mL, with no spilling. What changes?
The dissolved amount stays the same while concentration decreases. Only solvent is added. The same dissolved substance is spread through a larger solution volume, so the amount is conserved but the concentration becomes lower. For full control, write a short evidence sentence before checking this answer. If your result differs, identify whether the error came from selecting information, applying the relationship, choosing a form, or failing to reread the completed response.
8. Some water evaporates from 50 mL of a solution, and the dissolved substance remains in the container. What changes?
The dissolved amount stays the same while concentration increases. Evaporation removes solvent rather than creating dissolved substance. The unchanged amount is now present in a smaller volume, so the solution becomes more concentrated. For full control, write a short evidence sentence before checking this answer. If your result differs, identify whether the error came from selecting information, applying the relationship, choosing a form, or failing to reread the completed response.
9. Sample A and Sample B each contain 50 mL of the same solution type. A has concentration 4 units per 100 mL and B has 2 units per 100 mL. Compare the dissolved amount.
A contains more The volumes are equal, so concentration decides the comparison. The sample with concentration 4 contains more dissolved substance in the same volume. Equal volume alone would not justify equality. For full control, write a short evidence sentence before checking this answer. If your result differs, identify whether the error came from selecting information, applying the relationship, choosing a form, or failing to reread the completed response.
10. Two samples have the same concentration. One has 100 mL and the other has 150 mL. Which contains more dissolved substance?
The second sample Concentration is matched, so the larger solution volume contains proportionally more dissolved substance. The comparison uses both variables and does not confuse concentration with total dissolved amount. For full control, write a short evidence sentence before checking this answer. If your result differs, identify whether the error came from selecting information, applying the relationship, choosing a form, or failing to reread the completed response.
11. Water is added to 150 mL of a solution until its volume becomes 250 mL, with no spilling. What changes?
The dissolved amount stays the same while concentration decreases. Only solvent is added. The same dissolved substance is spread through a larger solution volume, so the amount is conserved but the concentration becomes lower. For full control, write a short evidence sentence before checking this answer. If your result differs, identify whether the error came from selecting information, applying the relationship, choosing a form, or failing to reread the completed response.
12. Some water evaporates from 50 mL of a solution, and the dissolved substance remains in the container. What changes?
The dissolved amount stays the same while concentration increases. Evaporation removes solvent rather than creating dissolved substance. The unchanged amount is now present in a smaller volume, so the solution becomes more concentrated. For full control, write a short evidence sentence before checking this answer. If your result differs, identify whether the error came from selecting information, applying the relationship, choosing a form, or failing to reread the completed response.
13. Sample A and Sample B each contain 50 mL of the same solution type. A has concentration 3 units per 100 mL and B has 3 units per 100 mL. Compare the dissolved amount.
equal amounts The volumes are equal, so concentration decides the comparison. Both variables match, so the dissolved amounts match. Equal volume alone would not justify equality. For full control, write a short evidence sentence before checking this answer. If your result differs, identify whether the error came from selecting information, applying the relationship, choosing a form, or failing to reread the completed response.
14. Two samples have the same concentration. One has 100 mL and the other has 150 mL. Which contains more dissolved substance?
The second sample Concentration is matched, so the larger solution volume contains proportionally more dissolved substance. The comparison uses both variables and does not confuse concentration with total dissolved amount. For full control, write a short evidence sentence before checking this answer. If your result differs, identify whether the error came from selecting information, applying the relationship, choosing a form, or failing to reread the completed response.
15. Water is added to 150 mL of a solution until its volume becomes 250 mL, with no spilling. What changes?
The dissolved amount stays the same while concentration decreases. Only solvent is added. The same dissolved substance is spread through a larger solution volume, so the amount is conserved but the concentration becomes lower. For full control, write a short evidence sentence before checking this answer. If your result differs, identify whether the error came from selecting information, applying the relationship, choosing a form, or failing to reread the completed response.
16. Some water evaporates from 50 mL of a solution, and the dissolved substance remains in the container. What changes?
The dissolved amount stays the same while concentration increases. Evaporation removes solvent rather than creating dissolved substance. The unchanged amount is now present in a smaller volume, so the solution becomes more concentrated. For full control, write a short evidence sentence before checking this answer. If your result differs, identify whether the error came from selecting information, applying the relationship, choosing a form, or failing to reread the completed response.
17. Sample A and Sample B each contain 50 mL of the same solution type. A has concentration 2 units per 100 mL and B has 4 units per 100 mL. Compare the dissolved amount.
B contains more The volumes are equal, so concentration decides the comparison. The sample with concentration 4 contains more dissolved substance in the same volume. Equal volume alone would not justify equality. For full control, write a short evidence sentence before checking this answer. If your result differs, identify whether the error came from selecting information, applying the relationship, choosing a form, or failing to reread the completed response.
18. Two samples have the same concentration. One has 100 mL and the other has 150 mL. Which contains more dissolved substance?
The second sample Concentration is matched, so the larger solution volume contains proportionally more dissolved substance. The comparison uses both variables and does not confuse concentration with total dissolved amount. For full control, write a short evidence sentence before checking this answer. If your result differs, identify whether the error came from selecting information, applying the relationship, choosing a form, or failing to reread the completed response.
19. Water is added to 150 mL of a solution until its volume becomes 250 mL, with no spilling. What changes?
The dissolved amount stays the same while concentration decreases. Only solvent is added. The same dissolved substance is spread through a larger solution volume, so the amount is conserved but the concentration becomes lower. For full control, write a short evidence sentence before checking this answer. If your result differs, identify whether the error came from selecting information, applying the relationship, choosing a form, or failing to reread the completed response.
20. Some water evaporates from 50 mL of a solution, and the dissolved substance remains in the container. What changes?
The dissolved amount stays the same while concentration increases. Evaporation removes solvent rather than creating dissolved substance. The unchanged amount is now present in a smaller volume, so the solution becomes more concentrated. For full control, write a short evidence sentence before checking this answer. If your result differs, identify whether the error came from selecting information, applying the relationship, choosing a form, or failing to reread the completed response.
A three-round practice ladder
Round 1: open-book accuracy
Complete five practice items while the mechanism section remains visible. For every item, underline or list the decisive evidence and write the rule in a short form. Accuracy matters more than speed here because you are constructing the decision pathway that later becomes automatic.
Round 2: closed-book retrieval
Close the guide and, after at least twenty minutes, solve five different items. Before looking back, reconstruct the rule in your own words and predict the kind of error you are most likely to make. Compare your process as well as your answer with the explanation.
Round 3: mixed transfer
Place four new items among questions from other topics. Mixed practice removes the heading that normally tells you which method to use. Your first task is now diagnosis: recognise when this guide’s principle applies, and also recognise when it does not.
Delayed transfer
Return the next day without rereading. State the controlling question, the principle and two contrasting examples from memory. Then invent one new example that differs in surface detail from every worked case. If you can justify it using the same mechanism, your understanding is becoming portable.
Return again three days later. Ask an adult or classmate to alter one important condition in your invented example. Predict what changes and what stays the same before solving. This “change one condition” routine exposes memorised slogans: a genuine model can explain the effect of the change.
Keep a four-column correction record: question cue, my first decision, evidence I missed, repaired rule. Do not copy a full model answer into the final column. A short rule that you can retrieve—combined with the missed evidence—is more useful for the next unfamiliar question.
Examination control
- Read the instruction and identify the exact object of the question.
- Mark only the information that controls the relationship; do not decorate every word or number.
- State the governing rule in a few words before committing to the answer.
- Carry out the spelling, calculation or interpretation carefully.
- Reread the answer inside the original context and check that the explanation matches the evidence.
If you become stuck, do not restart the whole paper in your head. Ask the narrow controlling question from the start of this guide. Eliminate interpretations that contradict explicit grammar, values, labels, keys or conditions. Then choose the response supported by the remaining evidence and move on.
A final check is not a second full solution. It targets predictable failure points: wrong word class or verb form, incorrect count, lost total, confused variables, ignored legend, or an unsupported visual assumption. A ten-second targeted check is often more useful than repeating the same reasoning unchanged.
For parents and tutors
Ask for evidence before correction: “Which word, value, condition, label or relationship controlled your answer?” The learner’s reply identifies the instructional need. A missing fact calls for knowledge review; a correct fact applied to the wrong situation calls for comparison practice; a sound method with an execution slip calls for a short accuracy routine.
Keep feedback specific and future-facing. Replace “be careful” with an action such as “count the observations before dividing,” “test award against interfere,” “compare concentration as well as volume,” or “read the diagram key before naming the symbol.” The learner can actually perform these actions on the next question.
Frequently asked questions
Must I memorise every worked case?
No. Learn the controlling relationship and use cases to practise recognising when it applies.
Why explain an answer that I already know?
Explanation exposes whether the result came from evidence or a lucky guess, and it builds a reusable method.
What should I do after one careless error?
Classify the error, repair the step that caused it, and test the repair on a nearby but different example.
How fast should I work?
Build accurate decisions first, then shorten the routine through timed mixed practice without removing its essential checks.
Can an unfamiliar context change the rule?
Surface details may change, but the mechanism remains until the question changes a condition that the mechanism depends on.
How do I know that I have mastered the idea?
You can retrieve the rule after a delay, solve a new example, explain why a tempting alternative fails and notice when the rule does not apply.
Next routes
Continue from the complete volume directory, revisit the original PSLE Learning Guide, and use the science hub for further subject routes. Preserve the method from this guide: identify the controlling evidence, apply the mechanism, explain the result and retrieve it again after a delay.