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GROW · SCIENCE · Lesson 4 of 6

The crystal has disappeared from view

Learning intention

Describe melting, freezing and dissolving and explain how the starting substances can be recovered in these examples.

Did the substance vanish, melt or dissolve?

A detective needs more than appearance.

Success looks like

  • Distinguish a change of state from mixing with a solvent.
  • Explain that dissolved sugar remains present.
  • Choose a suitable reverse process and state what is recovered.
Retrieval

GROW · SCIENCE · Lesson 4 of 6

State or mixture?

R1. Name a solid and a liquid.

R2. Does invisible always mean absent?

R3. What unit records mass?

I do

GROW · SCIENCE · Lesson 4 of 6

I identify a change of state

Ice and liquid water are the same substance.

Melting changes solid to liquid.

Freezing changes liquid to solid.

Melting and freezing of waterTwo macroscopic states of the same substance are connected by opposite arrows: warming can melt ice into liquid water; cooling enough can freeze water into ice. This diagram does not represent exact density or crystal structure.Same substance; different stateIcesolid waterLiquid waterMeltingenergy transferred inFreezingenergy transferred out
Melting and freezing of water
Diagram description

Two macroscopic states of the same substance are connected by opposite arrows: warming can melt ice into liquid water; cooling enough can freeze water into ice. This diagram does not represent exact density or crystal structure.

I do

GROW · SCIENCE · Lesson 4 of 6

I count what the model retains

Sugar molecules spread among water molecules.

The sugar symbols remain present.

A solution forms; the sugar has not melted here.

Sugar particle modelEight water symbols and four sugar symbols are retained in both panels. Sugar begins clustered and ends dispersed among water; no symbols disappear. Sizes, shapes and quantities are schematic.Dissolving: sugar remains in the mixtureBefore: sugar and waterAfter: sugar solutionBlue: water molecules. Orange: sugar molecules.Symbols and quantities are not to scale.
Sugar particle model
Diagram description

Eight water symbols and four sugar symbols are retained in both panels. Sugar begins clustered and ends dispersed among water; no symbols disappear. Sizes, shapes and quantities are schematic.

Continue within this stage’s shared time.

I do

GROW · SCIENCE · Lesson 4 of 6

I choose a route back

Letting water evaporate can leave sugar behind.

Simple open evaporation does not collect the water.

Reversible does not mean instant or effortless.

Recovering the dissolved solidA simplified scientific sequence: Sugar solution; Water evaporates over time; Sugar remains after drying. This recovers the sugar. Water is not collected by simple open evaporation; no heating is required here.Recovering the dissolved solidSugar solutionWater evaporatesover timeSugar remainsafter dryingThis recovers the sugar. Water is not collectedby simple open evaporation; no heating is required here.
Recovering the dissolved solid
Diagram description

A simplified scientific sequence: Sugar solution; Water evaporates
over time; Sugar remains
after drying. This recovers the sugar. Water is not collected
by simple open evaporation; no heating is required here.

Continue within this stage’s shared time.

We do

GROW · SCIENCE · Lesson 4 of 6

Process evidence tribunal

Go to interactive investigation

W1. Classify A and B: melting/freezing or dissolving.

W2. Use C and D to challenge “the sugar vanished”.

State what each piece of evidence contributes.

Constructed recordBeforeAfter
Sealed mass / g120120
Open recovery over daysSugar solutionDry sugar remains

Change tribunal: track the substance

Predict first, test the model, then explain using the evidence. Move at your own pace; paper W1–W3 tasks assess the same reasoning.

Decision 1 of 3

Ice becomes liquid water. What changed?

Choose, test, then explain together. Evidence diagrams appear only after your test. Diagram transitions explain the model; they do not represent real elapsed time. Use Pause model to stop transitions and model controls, or your device’s reduced-motion setting. The printed We do activity provides the paper route.

We do

GROW · SCIENCE · Lesson 4 of 6

Choose a reverse process

A tray contains melted ice. A second contains sugar solution.

Which needs enough cooling? Which needs water removed to recover sugar?

Continue within this stage’s shared time.

We do

GROW · SCIENCE · Lesson 4 of 6

Write a precise verdict

W3. Repair “Dissolving makes sugar into water”.

Use the particle model and recovery record.

Continue within this stage’s shared time.

Hinge

GROW · SCIENCE · Lesson 4 of 6

Sugar is stirred into room-temperature water

The crystals become invisible and a solution forms. What happened?

You do

GROW · SCIENCE · Lesson 4 of 6

Your independent investigation

Choose one response route.

Compare melting, freezing and dissolving.

Explain a route to recover the stated substance.

You do

GROW · SCIENCE · Lesson 4 of 6

Use the evidence

Track the substance before and after.

Use mass and recovery evidence appropriately.

Name what a chosen process actually collects.

Continue within this stage’s shared time.

You do

GROW · SCIENCE · Lesson 4 of 6

Check before sharing

Does my explanation answer the question?

Have I named the evidence or process?

Have I kept the conclusion within its limits?

Continue within this stage’s shared time.

Review

GROW · SCIENCE · Lesson 4 of 6

Compare and improve

Share one corrected process label.

Check the before-and-after substance.

Improve a disappearing or melting claim.

Review

GROW · SCIENCE · Lesson 4 of 6

A question worth investigating

Suggest one next question about this lesson’s evidence.

Choose a question whose answer would improve our model.

Continue within this stage’s shared time.

Exit

GROW · SCIENCE · Lesson 4 of 6

Show the science you can explain

E1. How is melting different from dissolving?

E2. Where is the sugar in a clear solution?

E3. How could sugar be recovered here?

My science task sheets

Choose one route with your teacher. Shared evidence and the exit sheet appear in every route. Your work stays here while the page is open; save it before closing.

1 • Shared evidence: change detectives

Records C and D are constructed examples. All work can be completed without a practical.

A • Ice record

Solid ice changes to liquid water when energy is transferred in. Later, enough cooling turns the liquid back into ice.

B • Sugar record

Sugar crystals are stirred into room-temperature water. The crystals are no longer visible; the liquid stays clear. No tasting is used.

C • Mass record

Constructed data: sealed container and contents are 120 g before dissolving and 120 g after. Nothing is added or removed while dissolving.

D • Recovery record

Constructed observation over several days: water leaves an open sugar solution by evaporation; dry sugar remains. No class trial or heating took place.

E • Distinction

Melting is a solid-to-liquid state change. Dissolving mixes a substance through a solvent; a clear solution can still contain the dissolved substance.

F • Boundary

The diagrams model the stated physical examples. “Easy to reverse” alone is not a complete test for whether any unknown change is physical or chemical.

2 • Supported route: choose the process

Use page 1. Word bank: melting / freezing / dissolving / solution.

S1. Ice becomes liquid water. This is …
S2. Liquid water becomes ice. This is …
S3. Sugar mixes through water. This is …

3 • Standard route: process report

Track the starting substance and the result.

ProcessStarting situationResult
Melting
Freezing
Dissolving sugar

4 • Stretch route: evidence and recovery

Explain the limits as well as the useful result.

5 • Exit and reflection

Use accurate process words.

Slide 1

TA Brief

Current stage

Objective

Describe melting, freezing and dissolving and explain how the starting substances can be recovered in these examples.

Preparation

Method precautions

Practical alternative

Use supplied observations and particle tokens to compare processes without heat, food handling or a time-dependent trial.

Access and regulation

Supported: Classify three cases and use a particle word bank.

Standard: Explain process differences and use mass/recovery evidence.

Stretch: Evaluate a disappearing-sugar claim and distinguish recovery of one component from both.

Regulation: Offer private writing, pointing, drawing or adult scribing. Allow pass-and-return for public questions and desk-based participation. Choose support from current learning evidence, not fixed ability labels.

Teacher answers

R1–R3

Valid solid/liquid examples; invisible does not mean absent; grams or kilograms.

W1–W3 / reverse routes

A melting and freezing; B dissolving. C shows unchanged total mass in a closed system; D shows recoverable sugar after water leaves. Enough cooling refreezes melted ice; evaporation removes water to recover sugar. W3 sugar remains distributed in a mixture with water, not converted into water.

Hinge A–C

A correct. B confuses dissolving with melting. C incorrectly claims the substance ceases to exist.

S1–S6

Melting; freezing; dissolving; sugar remains mixed through the water; evaporation removes water leaving sugar; no, simple open evaporation does not collect water.

N1–N4

Melting: ice→liquid water; freezing: liquid water→ice; dissolving: sugar plus water→sugar solution. N2 state change versus mixture formation with solvent. N3 same total mass plus sugar recovery contradict sugar vanishing; neither observation requires tasting. N4 allow water to evaporate over time; sugar remains, water is not captured by open evaporation.

T1–T4

T1 water remains water while state/arrangement changes; sugar and water remain present as a mixture, sugar molecules distributed among water molecules. T2 constant mass indicates no measured mass loss from the system but does not identify all substances; recovery specifically supports sugar remaining. T3 cooling refreezes water but does not universally separate every mixture into original components. T4 open evaporation leaves solid while water vapour escapes; recovering water requires capturing vapour and condensing it, explored next lesson.

E1–E4 / assessment

State change versus mixing; sugar remains distributed; evaporate water; freezing. Secure: distinguishes processes and gives an appropriate recovery route with its target. Re-teach by drawing one water substance versus two components in a solution. Reflection accepts a relevant alternative target.

Sources checked for this lesson

Word help

melting
A substance changing from solid to liquid.
freezing
A substance changing from liquid to solid.
dissolving
A substance mixing through a solvent to form a solution.
solution
A mixture in which the dissolved substance is distributed through a solvent.
reversible
Able to be changed back in the stated example or conditions.
evaporation
Liquid changing to gas at its surface.

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