A Journey through States of Water — Evidence, State Changes and Rates (2 of 3) · Learner pages

Lesson 1 · Test the source of outside droplets

Interpret whole-assembly mass readings and use comparisons without overstating the evidence.

Name or initials: ____________   Date: ____________

A mass reading includes everything placed on the balance. To investigate outside droplets, define the measured system and keep its components the same. Supplied readings avoid the need for a fragile container experiment.

1. Define what is weighed. The model reads the whole closed cold container: its lid, inside water, and any droplets still on the outside. The dry-outside start is 400.0 g. It is incorrect to call this only the mass of the inside water.
2. Compare like with like. Later the whole assembly with outside droplets reads 401.2 g. Under the supplied conditions nothing else was added, lost or changed on the balance. The gain is 1.2 g. Water moving from inside to outside while remaining on the assembly would not by itself increase this total.
3. Add relevant comparisons. Use supplied records or a teacher-managed comparison with an initially dry room-temperature closed container, the same balance procedure and a dry support. Check for spills, contact with the balance and instrument resolution. These checks help examine alternatives.
4. Limit the conclusion. A reliable mass gain with new outside droplets supports water arriving from the surroundings. It does not prove that every other tiny process is absent. A water-level mark showing no detectable fall also cannot exclude a change smaller than the method can detect.

Worked example: A supplied closed assembly begins at 520.0 g and later reads 520.8 g with droplets still attached outside. The measured gain is 0.8 g. If an inside drop merely moved onto the outside but stayed on the assembly, the total mass would remain the same; that redistribution alone cannot explain the gain.

1. What does the model’s 400.0 g starting reading include?

   1. Container, lid and all its contents on the balance · 2. Only the liquid water inside · 3. Only the outside air in the whole room

2. The same assembly increases from 400.0 g to 401.2 g. Its gain is…

   1. 401.2 g · 2. 801.2 g · 3. 1.2 g

3. Could water merely moving from inside to outside, while staying on the weighed assembly, explain a total mass gain by itself?

   1. Yes; outside drops have no mass · 2. No; that movement redistributes mass within the same measured system · 3. Yes; changing location creates mass

Discuss: Draw a boundary around everything on the balance. Calculate the supplied change and write a supported conclusion plus one remaining uncertainty.

Explain or demonstrate

For the supplied 520.0 g to 520.8 g closed-assembly record, calculate the change, identify the measured parts and explain why internal redistribution alone cannot cause the gain. Add one measurement limitation.

Evidence to include:

• System boundary named
• Mass gain calculated
• Conclusion and limitation separated

Lesson 2 · Follow changes of state

Name and correctly direct melting, freezing, evaporation and condensation.

Name or initials: ____________   Date: ____________

A state-change arrow connects a starting state to an ending state. Melting and freezing are opposite directions between solid and liquid; evaporation and condensation connect liquid and gas in opposite directions.

1. Read the arrow direction. In the diagram, begin with the state where an arrow starts, follow its direction and identify the ending state. Naming states without directions is not enough to identify a process.
2. Connect solid and liquid. Ice can melt as it gains energy from warmer surroundings. Liquid water can freeze when enough energy is removed under suitable conditions. Use supplied examples; no flame, hot wax or learner freezer experiment is required.
3. Connect liquid and gas. Liquid water can evaporate while gaining energy from its surroundings, even at room temperature. Water vapour can condense as conditions allow energy transfer to cooler surroundings. These are opposite state directions, not creation or destruction of water.
4. Keep the sequence and limits clear. A pathway can contain several changes, such as ice melting and the liquid later evaporating. Identify each step separately. The diagram shows four familiar processes; it is not a claim that these are the only possible state changes in all situations.

Worked example: A supplied observation starts with an ice cube, later shows liquid water, and still later a drier open tray. The first state change is melting. Evaporation can explain liquid water entering the surrounding air later. The first change should not be labelled evaporation simply because gas appears at the end of the whole pathway.

1. Solid ice changing to liquid water is…

   1. Freezing · 2. Condensation · 3. Melting

2. Liquid water changing to solid ice is…

   1. Evaporation · 2. Freezing · 3. Condensation

3. Which arrow correctly describes condensation?

   1. Water vapour → liquid water · 2. Liquid water → solid ice · 3. Liquid water → water vapour

Discuss: Draw a two-way solid–liquid–gas map with all four process names and arrows. Then describe a two-step pathway using the correct sequence.

Explain or demonstrate

Draw and label both directions between ice and liquid water, and both directions between liquid water and vapour. Explain one two-step pathway.

Evidence to include:

• Four arrows correctly directed
• Four names correctly matched
• Sequence explained

Lesson 3 · Compare evaporation rates fairly

Predict how conditions affect evaporation and design a comparison with one intended change.

Name or initials: ____________   Date: ____________

Evaporation rate depends on conditions. A useful investigation identifies what changes, what is controlled and what is measured. Predictions such as “faster” should be stated with the other conditions kept comparable.

1. Change the exposed surface. Compare equal starting amounts of water with different exposed surface areas under otherwise similar conditions. A larger exposed area usually gives faster evaporation. The pictures are schematic; use the stated equal amounts, not screen dimensions, to interpret the example.
2. Control other influences. Use comparable container material and starting water temperature, place both in the same surrounding air and record how much water starts in each. If several influences change at once, a different drying time cannot be attributed only to surface area.
3. Compare other factors separately. With other conditions comparable, warmer water/surroundings or more air movement can increase evaporation. Higher humidity usually reduces it. Air movement helps carry moist air away from the surface; the fan does not have to make the water hotter to aid drying.
4. Record and evaluate the results. Choose a clear observation rule, such as time until no visible liquid remains. Repeat when practical and keep unexpected records. A predicted relationship is not a universal promise for all materials, weather or measurement methods.

Worked example: An invented comparison begins with equal small amounts of water in similar-material shallow containers in the same room. The narrow exposed surface is dry after 42 minutes, the wide surface after 18 minutes. These supplied observations support faster drying for the wider surface under those conditions; they are not a promised drying time at home.

1. With equal water amounts and comparable other conditions, a larger exposed area generally gives…

   1. A guaranteed identical time in every room · 2. Faster evaporation · 3. No possible evaporation

2. To investigate exposed area, which should be kept the same?

   1. Starting water amount and surrounding conditions · 2. Only the label colour · 3. Nothing; change every factor

3. All else comparable, higher humidity usually makes evaporation…

   1. Always stop forever · 2. Create water from nothing · 3. Slower

Discuss: Plan one comparison for exposed area or air movement. Name the changed factor, three controls, the measured outcome and one possible limitation. Use supplied data if the setup is unavailable.

Explain or demonstrate

Plan a fair exposed-area comparison using equal water amounts. State the intended change, three controls, outcome and limitation.

Evidence to include:

• Area is the intended change
• Water amount/material/surroundings considered
• Clear timing rule and limit

Final check · Set 1

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

1. Why use an initially dry room-temperature closed container as a comparison?

   To guarantee both containers always gain identical mass / To change every condition at once / To help examine the effect of a cold surface under similar surroundings

2. A reliable mass gain and new outside droplets support which interpretation?

   A change of location inside always increases mass / Material arrived from outside the measured assembly / Water was created from nothing

3. An ice cube melts and the resulting water later evaporates. What is the order?

   Liquid → gas → solid / Solid → liquid → gas / Gas → liquid → solid

4. Evaporation at room temperature obtains energy…

   From the water and its surrounding environment as energy is exchanged / Only from an open flame / By destroying all matter

5. Invented drying times are 42 minutes for a narrow surface and 18 for a wide one. Which dried first?

   The wide surface / The narrow surface / They necessarily dried at the same time

6. One sample starts with twice as much water and is placed in a different room. Can its drying-time difference isolate surface area alone?

   Yes; only surface area can affect drying / Yes; controls are never needed / No; water amount and surroundings also changed

Final check · Set 2

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

1. A supplied assembly changes from 520.0 g to 520.8 g. What is the gain?

   0.8 g / 1040.8 g / 520.8 g

2. Which report is most careful?

   This proves all containers can never leak / Any disagreement means the observer is dishonest / The records support condensation from surrounding air; other small effects and measurement limits still need consideration

3. Why are condensation and freezing different?

   They always mean exactly the same process / Neither involves water / They begin and end in different states

4. What should a state-change diagram label include?

   Only the final state with no arrow / Starting state, ending state and correctly directed process / Only attractive colours

5. Which is a clearly stated measured outcome?

   Whether the learner prefers sunshine / Time until no visible liquid remains under a stated observation rule / Which label looks nicest

6. Why preserve an unexpected observation?

   It may reveal variation or an uncontrolled condition worth investigating / It must always be erased / It proves the learner was dishonest