S2 Science: Separating Mixtures (Paper 4 (error Clinic))

S2 Science: Separating Mixtures (Paper 4 (error clinic))

2026-11-14

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Tutor Prep Guide · Filtration, distillation, fractional distillation and chromatography with Rf calculations

S2 Science: Separating Mixtures (Paper 4 (error clinic))

This paper targets the usual errors: the order of filtering then evaporating, the funnel touching the wall, the meaning of a steady thermometer reading, Rf calculations and what a filtrate really is.

Direct answers　Add one line saying why after each answer, which separates a lucky guess from real understanding. When the word mixture appears, ask three things: does it dissolve, how far apart are the boiling points, and can chromatography tell the components apart.

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: S2 Science: Separating Mixtures
Level	S2

02　Questions (10 items)

FoundationWhat is the first step for a mixture of sand and salt solution?
FoundationWhat is obtained by evaporating that filtrate to dryness?
FoundationA pigment has an Rf value of 0.60. What fraction of the solvent front distance did the spot travel?
IntermediateWhy should the stem of the funnel touch the inside wall of the beaker?
IntermediateDuring distillation the thermometer stays steady at 100 °C. What is being distilled over?
IntermediateA spot moves 4.5 cm while the solvent front moves 7.5 cm. What is the Rf value?
Challenge200 g of solution contains eight percent salt. How much salt is left after evaporation?
ChallengeA sample gives Rf values of 0.45, 0.47 and 0.44. What is the mean?
ChallengeDoes distilled water conduct electricity, and why?
Error redoA student says the filtrate after filtration is pure water. What is the correct statement?

03　Answers and one-line notes

#	Answer	One-line note
1	Filtration, to remove the sand first	The sand does not dissolve, so filter it off first and then evaporate the filtrate to recover the salt.
2	Salt	The water vaporises and the dissolved salt is left as crystals in the dish.
3	Sixty percent of it	An Rf of 0.60 means the spot moved sixty percent of the distance travelled by the solvent front.
4	So the filtrate runs down the wall instead of splashing out	Filtrate dropping straight down splashes and is lost, while running down the wall keeps the flow smooth.
5	Water	Water boils at 100 °C at standard pressure, and a steady reading shows a single component in the vapour.
6	0.60	Four point five divided by seven point five gives 0.60.
7	16 g	Two hundred times zero point zero eight equals sixteen, so 16 g of salt remains.
8	0.45	The three add to 1.36 and dividing by three gives about 0.45, and repeats reduce the error.
9	Hardly at all, because it holds no dissolved ions	Conduction needs mobile ions, and distillation removes them during vaporisation and condensation.
10	The filtrate is still a solution holding the dissolved substances	Filtration only removes undissolved solids, and dissolved salt passes through the paper with the water.

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.

For separation questions ask two things: whether each component dissolves in water, and whether their boiling points or adsorption differ.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.