Lesson plan Grade 5 Science
Clearing Cloudy Water at Foxglen: A Grade 5 Coagulation Lesson
A grade 5 science lesson where students run a tabletop coagulation demonstration, adding a coagulant to cloudy water to see solids clump and settle.
Objectives
- Students will observe that mixing a coagulant into cloudy water produces clumps of solid material that settle out.
- Students will explain, using their observation, why a treatment plant adds a chemical step before filtering water.
- Students will record and compare how their cup of water looks before mixing, right after mixing, and after settling.
Vocabulary
- Coagulation
- Coagulation is the first cleaning step at a drinking water plant. Operators quickly mix in a chemical that makes tiny bits of dirt stop pushing each other away so they can start sticking together.
- Floc
- Floc is the fluffy clumps of dirt and treatment chemicals that form in the water during cleaning at a treatment plant. Floc looks like tiny snowflakes drifting in the water.
Also: settle, cloudy, turbid
Teacher overview
Foxglen's water treatment plant, a fictional plant used for this lesson, starts most mornings with the same problem: the water arriving from its reservoir is cloudy, carrying fine soil and organic particles too small to settle out on their own. Operators solve this with coagulation, a chemistry step that makes those tiny particles clump together into larger pieces called floc, which sink and can then be filtered out. This lesson lets students run a simplified version of the same process at their desks, stirring alum into a cup of deliberately muddied water. A common misconception this lesson addresses is the idea that filtering alone clears cloudy water; without coagulation first, many of the particles that cause cloudiness are far too small for an ordinary filter to catch, and students see the difference for themselves once the clumped floc, rather than the original fine sediment, settles to the bottom of the cup.
Procedure
Hook (5 min): Hold up a jar of cloudy water mixed ahead of time (tap water with a spoonful of garden soil). Ask students to predict what would happen if this water were poured straight through a coffee filter. Collect a few predictions on the board without confirming or denying them.
Direct instruction (10 min): Explain that some particles in cloudy water are so small that they pass straight through a filter's tiny holes, the same way fine sand slips through a kitchen strainer. Introduce coagulation: adding a chemical called a coagulant makes those tiny particles stick together into bigger clumps called floc, which are heavy enough to settle to the bottom on their own. Sketch a labeled sequence on the board: fine particles, coagulant added, particles clump into floc, floc settles, clearer water remains on top.
Guided demonstration (10 min): In groups of three or four, students receive a cup of the same cloudy water and a measured half-teaspoon of alum. Model stirring the alum into the water for about thirty seconds, then setting the cup down without disturbing it further. Each group writes a one-word description of the water's appearance the moment stirring stops. Remind students not to taste the water or the alum, and have everyone wash their hands after the activity.
Observation and data collection (15 min): Groups check their cups every five minutes for fifteen minutes, three checkpoints in total, recording what they see at each one: whether clumps have formed, whether a layer has settled at the bottom, and how the water above that layer compares to how it looked at the start.
Class discussion and formative check (5 min): Ask each group to report its fifteen-minute observation. Then pose the formative check: "If we skipped the alum and poured our cloudy water straight through a coffee filter right now, would it come out clear? Thumbs up for yes, thumbs down for no." Most students should signal no; use any thumbs-up responses to prompt a brief re-explanation of why fine particles pass through filter paper.
Closure (5 min): Students complete one written sentence as an exit ticket: "Coagulation helps a treatment plant because ___."
From Water for Schools (waterforschools.org). This material is in the public domain (CC0) and may be copied, edited, and shared freely.
Answer Key
- Formative check: No, thumbs down. Without the coagulant, the fine particles causing the cloudiness are too small to be caught by a coffee filter's pores, so the water would pass through still cloudy.
- Exit ticket: Answers will vary but should state that coagulation helps a treatment plant because it clumps together fine particles that filtering alone cannot remove, forming heavier floc that settles out and leaves clearer water for the filtering step that follows.
- Observation check: Groups should report increasing clarity in the water above the settled layer at each of the three checkpoints, with visible clumps of floc appearing well before the fifteen-minute mark in most cups.
Differentiation
Support (below grade level)
Pre-fill most of the labeled sequence diagram, leaving only the words "floc" and "settle" for students to add themselves. Reduce the observation checkpoints from three to two, at the start and at fifteen minutes, so students track fewer data points at once.
Extension (above grade level)
Ask advanced groups to prepare a second cup with double the amount of alum and compare how quickly floc forms and settles against the standard cup, then explain in writing whether adding more coagulant always makes water clear faster.
ELL supports
Pre-teach "cloudy," "clump," "settle," and "coagulation" using the four-step sequence diagram posted at each group's table as a visual reference. Allow students to complete the exit ticket sentence orally with a partner before writing it independently.
Extensions
Invite a local water or wastewater operator to describe, in a short class visit or a recorded message, how their treatment plant's coagulation step compares with the classroom demonstration, including what coagulant chemical the plant actually uses and roughly how long full-scale settling takes there.