A Journey through States of Water — States, Evaporation and Condensation (1 of 3) · Answer guide

Lesson 1 · Compare three states of water

Distinguish state properties while recognising ice, liquid water and water vapour as the same substance.

1. An ice cube melts to liquid water. The result is…

   Answer: The same substance in a different state. Melting changes the state of water.

2. A liquid water sample is poured into a wider container without loss. What can change?

   Answer: Its shape and height, while its volume stays the same. The same quantity of liquid takes a different container shape.

3. Water vapour itself is…

   Answer: An invisible gas. Visible mist contains droplets; the vapour gas is invisible.

Discuss: Create a three-row state table with shape, spreading behaviour and a model limitation. Use supplied observations rather than heating water.

Teaching note: A liquid retaining its volume during a spill-free transfer is different from a substance changing volume when it freezes or melts. Do not use “same substance” to mean every property stays identical. Open responses need discussion; they are not automatically marked.

Explain or demonstrate

Compare the three states in a table. Explain why shape changes do not always mean a new substance, and name one property the drawing does not establish.

Evidence to include:

• Three states distinguished
• Substance identity preserved
• A model limit stated

Review guide:

• 1 point: solid/liquid/gas behaviours correct
• 1 point: all three are water
• 1 point: no unsupported claim of identical volume or density across state change

Example response: Ice keeps its own shape; liquid water takes a container shape but retains its volume during transfer without loss; vapour spreads through available space. They are states of water. The drawings do not establish equal density across the states.

Lesson 2 · Explain water disappearing from view

Distinguish evaporation from leakage or absorption and recognise evaporation at room temperature.

1. A wet tray dries with no observed spill. Evaporation means water has…

   Answer: Changed to vapour in the surrounding air. The water changes state and disperses; it remains matter.

2. Can water evaporate at room temperature?

   Answer: Yes; boiling is not required. Ordinary drying shows evaporation can occur at room temperature.

3. A puddle on soil shrinks. Which conclusion is most careful?

   Answer: Absorption and evaporation may both contribute. The observation alone does not isolate one process.

Discuss: Write an observation-and-explanation table for a drying tray. Include one alternative explanation and a check that would help distinguish it.

Teaching note: Evaporation is not the same as sinking into soil, and it does not require boiling. Invisible vapour remains water matter in the surroundings. Open responses need discussion; they are not automatically marked.

Explain or demonstrate

For a supplied dry-tray record, separate observations from an evaporation explanation and propose one check for an alternative pathway.

Evidence to include:

• Observed surface change stated
• Vapour explanation identified as an inference
• Spill or underside check proposed

Review guide:

• 1 point: observation and inference distinguished
• 1 point: no destruction-of-water claim
• 1 point: relevant alternative check

Example response: The tray began wet and later looked dry; no spill was recorded. Evaporation is an explanation: water entered the air as vapour. I would check the underside and support for moisture before ruling out seepage or a spill.

Lesson 3 · Explain droplets on a cold surface

Explain condensation using the origin, state and position of water on a cold container.

1. Condensation is the change from…

   Answer: Water vapour to liquid water. Gas-to-liquid is condensation.

2. Where can the water for outside droplets on a cold closed bottle come from?

   Answer: Water vapour in surrounding air. Surrounding air can supply water vapour that condenses.

3. What is the state of the visible droplets outside the bottle?

   Answer: Liquid. Droplets are small amounts of liquid water.

Discuss: Draw two labelled regions: inside the container and surrounding air. Show the proposed source and state change for outside droplets, then state a useful comparison.

Teaching note: Outside droplets need not be water that leaked from inside. A cold container does not manufacture water, and condensation is gas-to-liquid rather than liquid-to-gas. Open responses need discussion; they are not automatically marked.

Explain or demonstrate

Explain the outside droplets in the supplied closed-bottle comparison. Include water’s origin, state change and a limit on the conclusion.

Evidence to include:

• Surrounding air identified
• Vapour-to-liquid transition stated
• Actual conditions acknowledged

Review guide:

• 1 point: air can supply invisible water vapour
• 1 point: condensation forms liquid outside
• 1 point: coldness alone is not a universal guarantee of visible droplets

Example response: Water vapour in the surrounding air can cool near the cold bottle and condense to liquid on its outside. The bottle does not create the water. Whether droplets form depends on the actual surface and air conditions.

Final check · Set 1

Try one set after the lessons. Use the other set after reviewing any errors.

1. Which state spreads through the available space without a fixed shape or volume?

   Gas. Gas spreads through available space rather than retaining a fixed shape and volume.

2. Does “ice and water are the same substance” mean their density must be identical?

   No; some properties differ between states. State changes can alter properties while retaining substance identity.

3. Which activity fits this lesson?

   Observe a small amount of clean water on a stable tray. A small room-temperature clean-water observation is sufficient.

4. Why does a visible white plume not show that water-vapour gas is white?

   The visible part contains tiny liquid droplets. Gaseous water is invisible; droplets can form in the surrounding cooler air.

5. Which comparison is useful?

   Similar cold and room-temperature closed containers in the same surrounding air. The comparison helps examine the role of surface temperature while limiting other changes.

6. Does every cold object always develop visible water droplets?

   No; surface and air conditions matter. Condensation depends on conditions including moisture in the air and how cold the surface is.

Final check · Set 2

Try one set after the lessons. Use the other set after reviewing any errors.

1. A visible white mist near water is evidence of…

   Tiny liquid droplets in the air. Small droplets scatter light and are visible; gaseous water vapour is invisible.

2. Which statement keeps the model’s limit clear?

   The panels show everyday behaviour, not literal particle arrangements. A teaching schematic should not be read as microscopic or complete physical evidence.

3. A non-porous tray observation supports evaporation. What remains too broad?

   Claiming that all shrinking outdoor puddles lose water only this way. A conclusion about one setup does not rule out other mechanisms elsewhere.

4. Which pairing is correct?

   Evaporation: liquid to gas; absorption: liquid enters another material. The two words describe different processes.

5. Dew formation is related to…

   Water vapour becoming liquid on a sufficiently cool surface. Condensation can produce dew on cool surfaces.

6. Which statement keeps substance and state distinct?

   The vapour and condensed droplets are both water in different states. Water retains its identity through this state change.