Pearson Edexcel GCSE Combined Science · C2

States of matter and mixtures

50 revision questions with answers for C2 States of matter and mixtures in Pearson Edexcel GCSE Combined Science (spec 1SC0). Practise with flashcards, a topic quiz, a random quiz across the course, 5 crosswords, or read every question and answer below. Not official Pearson material.

All 50 questions and answers

Question 1 · Spec C2.1
Describe particles in a solid.
Answer:
They are closely packed in fixed positions and vibrate about those positions.
Question 2 · Spec C2.1
Describe particles in a liquid.
Answer:
They are close together but irregularly arranged and can move past one another.
Question 3 · Spec C2.1
Describe particles in a gas.
Answer:
They are widely spaced and move rapidly and randomly in all directions.
Question 4 · Spec C2.2
Name the changes from solid to liquid and liquid to solid.
Answer:
Melting and freezing, respectively.
Question 5 · Spec C2.2
Name the changes from liquid to gas and gas to liquid.
Answer:
Boiling or evaporation, and condensation, respectively.
Question 6 · Spec C2.2
What is sublimation?
Answer:
A direct change from solid to gas without becoming liquid.
Question 7 · Spec C2.3
Why does melting require energy?
Answer:
Energy is needed to overcome some attractions so particles can move past one another.
Question 8 · Spec C2.3
Why does a gas condensing transfer energy to its surroundings?
Answer:
Particles become closer together and form stronger interactions, releasing energy.
Question 9 · Spec C2.4
A substance melts at -5 °C and boils at 70 °C. Find its state at 25 °C.
Answer:
Liquid: 25 °C lies between the melting and boiling points.
Question 10 · Spec C2.2
Why is melting a physical change?
Answer:
No new substance forms and freezing can restore the original solid.
Question 11 · Spec C2.5
What is a chemically pure substance?
Answer:
One element or one compound, with no other substances mixed in.
Question 12 · Spec C2.5
Why is everyday 'pure juice' chemically a mixture?
Answer:
It contains multiple substances, including water, sugars and other compounds.
Question 13 · Spec C2.6
How does melting behaviour distinguish a pure solid from a mixture?
Answer:
A pure solid has a sharp melting point; a mixture typically melts over a range.
Question 14 · Spec C2.6
A solid melts from 118 to 124 °C instead of sharply at 123 °C. What does this suggest?
Answer:
It is likely impure; measurement quality should also be checked.
Question 15 · Spec C2.7
Which method separates insoluble sand from water?
Answer:
Filtration; sand is the residue and water passes through as filtrate.
Question 16 · Spec C2.7
Which method obtains a dissolved solid as crystals?
Answer:
Crystallisation, by concentrating the solution and allowing crystals to form.
Question 17 · Spec C2.7
Which method recovers water from salt solution?
Answer:
Simple distillation: evaporate the water and condense its vapour separately.
Question 18 · Spec C2.7
When is fractional distillation useful?
Answer:
Separating mixed liquids with different boiling points.
Question 19 · Spec C2.7
When is paper chromatography useful?
Answer:
Separating and comparing soluble components, such as dyes in ink.
Question 20 · Spec C2.8
How could a mixture of sand and salt be separated into its solids?
Answer:
Dissolve the salt, filter off and dry the sand, then crystallise salt from the filtrate.
Question 21 · Spec C2.8
Why does filtration not remove dissolved salt from water?
Answer:
Dissolved ions pass through the filter with the water.
Question 22 · Spec C2.8
Why can a mixture be separated using physical methods?
Answer:
Its components are not chemically combined and retain their individual properties.
Question 23 · Spec C2.11 · Core practical
How can simple distillation investigate an ink's solvent?
Answer:
Heat the ink, collect condensed solvent vapour and observe the non-volatile dyes remaining behind.
Question 24 · Spec C2.11 · Core practical
What is the condenser's function?
Answer:
It cools vapour, transferring energy away so the vapour becomes a collected liquid.
Question 25 · Spec C2.11 · Core practical
Why must the distillation apparatus not be sealed?
Answer:
Heating a sealed system can cause dangerous pressure buildup.
Question 26 · Spec C2.9
What are the mobile and stationary phases in paper chromatography?
Answer:
The solvent is the mobile phase; the paper contains the stationary phase.
Question 27 · Spec C2.9
Why do dyes travel different distances on chromatography paper?
Answer:
They have different affinities for the mobile and stationary phases, so move at different rates.
Question 28 · Spec C2.9
Which dye travels farther: one favouring the solvent or the stationary phase?
Answer:
The dye favouring the solvent travels farther under the same conditions.
Question 29 · Spec C2.11 · Core practical
Why draw the baseline in pencil?
Answer:
Graphite does not dissolve and travel with the solvent as ink might.
Question 30 · Spec C2.11 · Core practical
Why must the solvent initially be below the ink spots?
Answer:
Otherwise the dyes could dissolve into the solvent reservoir instead of moving up the paper.
Question 31 · Spec C2.11 · Core practical
Why apply small concentrated ink spots?
Answer:
They produce sharper separated spots and reduce overlapping bands.
Question 32 · Spec C2.11 · Core practical
Why let a spot dry before adding more ink?
Answer:
It increases dye concentration without making the initial spot spread too widely.
Question 33 · Spec C2.11 · Core practical
Why mark the solvent front immediately after removing the paper?
Answer:
The solvent may evaporate, making its furthest position difficult to identify.
Question 34 · Spec C2.10
State the Rf equation.
Answer:
Rf = distance travelled by substance / distance travelled by solvent front, measured from the baseline.
Question 35 · Spec C2.10
Where should the distance to a dye spot be measured?
Answer:
From the baseline to the centre of the spot.
Question 36 · Spec C2.10
A dye travels 24 mm and solvent 60 mm. Find Rf.
Answer:
Rf = 24/60 = 0.40.
Question 37 · Spec C2.10
A dye has Rf 0.75 with a 40 mm solvent distance. Find its distance.
Answer:
0.75 × 40 = 30 mm.
Question 38 · Spec C2.10
Why does Rf have no unit?
Answer:
The distance units cancel in the ratio.
Question 39 · Spec C2.10
Why compare Rf values using the same solvent and conditions?
Answer:
Rf depends on the experimental conditions, so different conditions can give different values.
Question 40 · Spec C2.10
What do several spots from one sample show?
Answer:
The sample contains more than one separated component and is a mixture.
Question 41 · Spec C2.10
Does one chromatography spot prove purity?
Answer:
No. Different substances may overlap or be undetected; it is evidence consistent with purity.
Question 42 · Spec C2.10
Why run known substances beside an unknown sample?
Answer:
Matching spots or Rf values under the same conditions help identify components.
Question 43 · Spec C2.11 · Core practical
Why might changing solvent improve an inconclusive chromatogram?
Answer:
A different solvent may separate components that overlapped in the first run.
Question 44 · Spec C2.12
What is potable water?
Answer:
Water safe to drink, with sufficiently low harmful microbe and chemical levels.
Question 45 · Spec C2.12
What does sedimentation remove in water treatment?
Answer:
Settling separates suspended material that sinks under gravity.
Question 46 · Spec C2.12
Why is water filtered after sedimentation?
Answer:
Filtration removes smaller suspended particles left in the water.
Question 47 · Spec C2.12
Why is treated water chlorinated?
Answer:
To kill harmful microorganisms and reduce disease risk.
Question 48 · Spec C2.12
How can distillation make seawater potable?
Answer:
Water evaporates and is condensed separately, leaving dissolved salts behind.
Question 49 · Spec C2.12
Why is potable water not necessarily chemically pure?
Answer:
It can contain dissolved substances at safe concentrations.
Question 50 · Spec C2.12
Why must water used in chemical analysis contain no dissolved salts?
Answer:
Dissolved ions could react or give misleading results, contaminating the analysis.

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