P3 General Studies: Dissolving And Separation (Paper 4 (error Clinic))

P3 General Studies: Dissolving and Separation (Paper 4 (error clinic))

2026-11-13

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P3 General Studies: Dissolving and Separation (Paper 4 (error clinic))

Paper four targets past errors: treating dissolving as disappearing or melting, filtering to recover salt, mistaking solution mass, the scope of saturation, and forgetting to scale crystallisation by the mass of water.

Direct answers　For every item write the solute, solvent and solution masses separately, then judge the method, and only then work out the percentage.

01　Paper details (check answers afterwards)

Item	Detail
Questions	10
Suggested time	20
Difficulty mix	Foundation 3 · Intermediate 3 · Challenge 3 · Error redo 1
Chapter	Chapter: P3 General Studies: Dissolving and Separation
Level	parts of a closed circuit, conductors against insulators, series against parallel, adding up battery voltage, and electrical safety

02　Questions (10 items)

FoundationSugar solution is a solution. What kind of material is a solution?
FoundationIf salt solution is filtered, does the salt stay on the filter paper?
FoundationWhich tool separates iron powder from sand?
IntermediateAt 20 degrees Celsius, 100 g of water already holds 36 g of dissolved salt and is saturated; another 10 g of salt is added. What is the total mass in the cup?
IntermediateA 150 g salt solution contains 30 g of salt. What percentage of the solution is salt?
IntermediateAt 20 degrees Celsius, 100 g of water dissolves at most 36 g of salt. How much salt can 300 g of water dissolve?
Challenge500 g of salt solution gives 25 g of salt when evaporated to dryness. If it is only evaporated down to 200 g of solution with no salt crystallising, what percentage is salt?
Challenge30 g of sand is mixed with 20 g of salt. What percentage of the mixture is salt?
ChallengeA salt dissolves 36 g per 100 g of water at 20 degrees and 40 g at 80 degrees. 250 g of water saturated at 80 degrees is cooled to 20 degrees. How much salt crystallises out?
Error redoA classmate treats dissolving as melting. What is wrong?

03　Answers and one-line notes

#	Answer	One-line note
1	A uniform mixture.	The sugar is spread evenly through the water, so every part has the same concentration.
2	No, the salt passes through with the water.	The salt is dissolved, so its particles are smaller than the holes in the paper.
3	A magnet.	The magnet picks up the iron powder only, leaving the sand behind.
4	146 g, of which 136 g is solution	The solution is 136 g and the undissolved salt is 10 g, making 146 g.
5	20.0 percent	Thirty divided by one hundred and fifty times one hundred gives 20.0 percent.
6	108.0 g	Thirty-six times three equals 108.0.
7	12.5 percent	The salt is still 25 g in 200 g of solution, so twenty-five over two hundred gives 12.5 percent.
8	40.0 percent	The mixture is 50 g, so twenty over fifty gives 40.0 percent.
9	10.0 g	The gap is four grams per 100 g of water, so 250 g gives two and a half times that, which is 10.0 g.
10	Melting only changes the state through heat, while dissolving spreads particles through a solvent; they are different.	Ice melts into water without any solvent, but sugar needs water before it can dissolve.

04　What to do after marking

After marking, redo only the wrong items and write down which step went wrong (formula, unit, or misread number).
Repeat the same item two days later; move to the next paper only when both attempts are correct.
Parents only need the answer and note columns; there is no need to explain every item.

With all four done, go back to the chapter page and revise the three parts of a closed circuit plus three safety habits.Tutor Registration →

Questions and answers are written originally by the TutorZone team and are not taken from any school, publisher or examination authority paper. Every value is checked by computer.