Evaporation Detectives: Water Changes

Overview

Lesson 2 of 6 in Our Blue Planet: Water Cycle. Students investigate evaporation and condensation through a chalk-and-puddle investigation, compare water loss in different conditions, and model condensation using a chilled container or covered cup.

Learning intentions

• WALT investigate how water changes state through evaporation and condensation.
• WALT make careful observations and identify variables in a fair test.
• WALT explain that water vapour is an invisible gas.

Success criteria

• I can distinguish evaporation from condensation.
• I can record observations clearly using words, drawings and measurements.
• I can identify the independent, dependent and controlled variables.
• I can explain that liquid water can become invisible water vapour and later condense.

Curriculum links

• Material World: understanding that substances can change state and that heating and cooling affect particles.
• Nature of Science – Investigating in Science: asking questions, observing, measuring, identifying variables and using evidence.
• Nature of Science – Communicating in Science: using scientific vocabulary, diagrams, tables and explanations.
• Key competencies: thinking; managing self; participating and contributing; using language, symbols and texts.

Lesson structure (45 minutes)

1. 0–5 min – Retrieve prior learning Open with the retrieval and hook slides. In pairs, students quickly sort or call out examples of solids, liquids and gases, then answer: “Where does a puddle go when it disappears?” Collect ideas without correcting every misconception. Establish that this is lesson 2 of the water-cycle enquiry.

2. 5–10 min – Teach the key ideas Use the states-of-water teaching slides to introduce evaporation as liquid water changing into an invisible gas, and condensation as water vapour changing back into liquid. Emphasise that evaporation can happen without boiling and that cooling encourages condensation. Students sketch arrows between liquid water and water vapour on the evaporation and condensation investigation sheet.

3. 10–13 min – Safety and practical roles Explain that groups will use room-temperature water, chalk or a damp cloth, trays or plates, cups and an ice-chilled container. Do not taste materials; wipe spills immediately; handle ice and glass carefully; keep water away from electrical equipment. Form nine mixed-ability teams of four and assign equipment manager, recorder, observer and reporter. Hand out the scientific variables sort cards and have teams identify which cards describe independent, dependent and controlled variables before beginning.

4. 13–27 min – Recreate and compare Give each team two equal small amounts of water on a tray or plate. Mark one with chalk or outline a “puddle” area; leave one in a relatively still condition and place the other where it experiences a different condition, such as greater airflow or a warmer location approved by the teacher. Students predict which will lose water faster, then record starting appearance, condition, time and changes on the evaporation and condensation investigation sheet. They should not claim a final result before comparing observations. Circulate, question groups about what they changed and what they kept the same, and support accurate use of “evaporated”.

5. 27–35 min – Model condensation Demonstrate rather than circulate hot or fragile equipment. Place ice in a container or around a covered cup containing room-temperature water. Students observe the outside surface and discuss: “Where did these droplets come from?” Use the condensation demonstration slides to show that the droplets formed when invisible water vapour in the air cooled and condensed. Students draw and label the model, including liquid water, water vapour and condensation.

6. 35–41 min – Explain the evidence Teams compare results and prepare a 30-second report: their prediction, what they observed, the variable changed, the variables kept the same, and whether the evidence supported their prediction. Prompt students to distinguish water disappearing through evaporation from droplets appearing through condensation. Invite two or three reports and address the misconception that evaporated water has vanished.

7. 41–45 min – Plenary and formative check Return to the plenary question slides. Students complete the final section of the evaporation and condensation investigation sheet: “Evaporation is…”, “Condensation is…”, and “Water vapour is…”. Collect sheets or sample responses as students leave, checking for a correct process, evidence-based observation and a sensible variable.

Resources

• the evaporation and condensation teaching deck
• the evaporation and condensation investigation sheet
• the scientific variables sort cards
• Nine trays or plates, nine small cups and room-temperature water
• Chalk or damp cloths; rulers or markers if available
• Ice and one clear container or covered cup for teacher demonstration
• Paper towels, cloths and a rubbish bin
• Timer or classroom clock
• Safety glasses if available, especially for the demonstration

Assessment

• Observe team discussions and variable-card sorting; question students individually about evaporation and condensation.
• Check investigation sheets for a prediction, clear observations, identified variables and labelled diagrams.
• Use the plenary responses to identify students who still think water vapour is visible or that evaporation only occurs when water boils.

Differentiation

• Provide a step-by-step practical sheet with icons, sentence starters, a partially completed results table and a word bank: liquid, gas, vapour, evaporate, condense, variable.
• Use mixed-ability roles and allow oral recording, labelled drawings, shared scribing or speech-to-text. Pair EAL learners with supportive peers and pre-teach the two process words using gestures and diagrams.
• Demonstrate the investigation before teams begin; reduce equipment choices for students needing SEN support and assign a predictable role such as observer or equipment manager.
• Extend confident learners by designing a fair test of temperature, surface area or airflow, stating a prediction and explaining how the findings apply to drying clothes or local weather.