LF-17 · TEACHER LESSON PLAN

Magic milk experiment

Why a drop of dish soap sends color swirling across a plate of milk

ChemistryGrades 2–62 sessions · 25–30 min totalHazard low; check allergiesNGSS 5-PS1-3

01 //

Driving question

START THE LESSON WITH THISA drop of dish soap makes food coloring streak across milk, but whole, 2% and skim milk may show different patterns. What happened and why?

02 //

Learning objectives

Students predict which milk condition may show the clearest color movement without assuming whole milk must win.
Students classify swirl intensity on the same anchored 1–5 scale and record how long visible motion lasts.
Students explain how soap changes surface conditions and milk interactions while food coloring traces the fluid movement.

03 //

Standards

Dimension	Alignment
Performance expectation	5-PS1-3Make observations and measurements to identify materials based on their properties. (Partial alignment: students observe and compare how different milks behave with soap; the lesson is about surface behavior, not identifying an unknown material.)
Practices	SEP 3Plan and carry out investigations (investigations that control variables, observations and measurements as evidence). SEP 4Analyze and interpret data.
Core idea	5-PS1 core ideaMeasurements of a variety of properties can be used to identify materials.
Crosscutting	Cause and effectCause and effect relationships are routinely identified, tested, and used to explain change.

Standards text paraphrased from nextgenscience.org. Alignment is partial; this hands-on activity does not cover every part of the performance expectation.

03A //

State standards crosswalk

Use the row as a planning crosswalk, then confirm local district pacing and grade placement. “Partial” labels describe a skill connection, not full mastery of the complete standard.

State	Verified standard	How this lesson aligns	Official source
California	CA NGSS 5-PS1-3	Limited connection: students observe and compare sample behavior, but this investigation does not identify an unknown material by its properties.	Open standard ↗
Texas	Science.6.6(B)	Partial connection: students compare liquid samples after mixing, but do not classify pure substances and homogeneous or heterogeneous mixtures.	Open standard ↗
Florida	SC.8.P.8.4	Limited connection: the activity observes surface behavior, but does not classify substances using the listed characteristic physical properties.	Open standard ↗
New York	NYSSLS 5-PS1-3	Limited connection: students make observations of material behavior, but do not identify unknown materials as required by this expectation.	Open standard ↗
Pennsylvania	STEELS 3.2.2.A	Partial connection: students investigate observable behavior of materials, but compare milk formulations rather than classify different materials by their properties.	Open standard ↗

04 //

Materials and prep timeline

PER GROUP

10 identical level shallow plates: 3 fresh trials each for whole, 2% and skim milk plus 1 whole-milk clean-swab control; 60 mL per plate
Food coloring: 3 colors, 1 drop of each color per plate; use marked spacing and the same wait
10 fresh cotton swabs (one clean control, nine soapy trials)
Dish soap: exactly 1 drop on each test swab; 1 dropper and 1 timer
Eye protection for each student
Paper towels and a spill tray

TEACHER ONLY

Check dairy and food-coloring allergies before setup
One printed student sheet per student

CLASS-SIZE KIT PLANNER

One per-group kit contains every item in the team materials list above. Groups are balanced around the listed 2–3 students target.

Students	Groups	Per-group kits	Student sheets	Suggested group split
20	7	7 complete kits	20 copies	6 groups of 3 and 1 group of 2
25	9	9 complete kits	25 copies	7 groups of 3 and 2 groups of 2
30	10	10 complete kits	30 copies	10 groups of 3

SESSION 1 · 15 MINSet up and run matched trials

Prepare the no-soap control and nine fresh test plates. Add equal 60 mL portions, matched dye drops, then use one measured soap drop and center touch for each trial.

SESSION 2 · 10–15 MINRate and compare the evidence

Time until movement has been absent for five seconds (cap at 60 s), apply the shared 1–5 visual anchors, and compare every raw trial, each mean, and range.

04A //

Lab figures and data visuals

Reviewed article images support the lesson flow. Use the tables and student sheet to record actual observations; pictured patterns are not target results.

Food coloring swirls across a plate of milk where a soap-dipped cotton swab touches the surface. — **Soap sets the colors in motion.**Food coloring traces the movement created when a small amount of dish soap touches the milk surface.

A holographic close-up shows soap molecules around milk fat globules and color tracing surface flow. — **Soap changes surface conditions.**Dish soap lowers surface tension and interacts with fat globules; the dye makes the resulting fluid motion visible.

AI-generated classroom illustration titled Soap Moves Color Through Milk, showing food-color tendrils spreading across a milk plate as a soapy cotton swab touches the surface. — **The soap makes the color move across the milk.**Food coloring makes the motion visible. The trial table below records fresh tests and the same observation window for every milk type.

04B //

Printable shopping list

TEACHER PREP · Magic milk experiment

Shopping and staging checklist

Multiply the per-group kit contents by the class-size planner. The teacher section includes teacher-provided materials and setup or safety notes.

PER-GROUP KITS

10 identical level shallow plates: 3 fresh trials each for whole, 2% and skim milk plus 1 whole-milk clean-swab control; 60 mL per plate
Food coloring: 3 colors, 1 drop of each color per plate; use marked spacing and the same wait
10 fresh cotton swabs (one clean control, nine soapy trials)
Dish soap: exactly 1 drop on each test swab; 1 dropper and 1 timer
Eye protection for each student
Paper towels and a spill tray

TEACHER-PROVIDED MATERIALS + SETUP RULES

Check dairy and food-coloring allergies before setup
One printed student sheet per student

QUANTITIES BY CLASS SIZE

Material	Per group kit	20 students	25 students	30 students
Shallow plates (9 tests + 1 clean-swab control)	10	70	90	100
Milk (10 × 60 mL)	600 mL	4.2 L	5.4 L	6 L
Fresh cotton swabs	10	70	90	100
Dish soap	9 measured drops	63 drops	81 drops	90 drops
Eye protection (one pair per student)	2–3 pairs	20 pairs	25 pairs	30 pairs
Food coloring (3 colors)	10 drops per color	70 drops per color	90 drops per color	100 drops per color
Soap dropper and timer	1 of each	7 of each	9 of each	10 of each
Spill tray and paper towels	1 tray + 2 towels	7 trays + 14 towels	9 trays + 18 towels	10 trays + 20 towels
Student sheets	1 per student	20	25	30

Prepare 7 kits for 20 · 9 kits for 25 · 10 kits for 30 students.

05 //

Lesson flow

Minutes	What happens
S1 · 0–2	Engage Show the first soap touch and ask what the moving color reveals. Students predict whether one milk type will stand out or whether the results may be similar.
S1 · 2–5	Explore Pour 60 mL into each identical level plate; use the same three dye drops at marked positions and the same wait time.
S1 · 5–8	Use a clean dry swab on the separate control plate. Test each milk type on three fresh plates, with a new swab and exactly one soap drop each time.
S1 · 8–15	Explore Touch the center once and start the timer at contact. Stop after five seconds without visible motion; record 60+ if the one-minute cap is reached first.
S2 · 0–5	Explain Rate each pattern with shared anchors: 1 no streaking, 2 short/local, 3 about one-third of the plate, 4 about two-thirds, 5 vigorous streaks across most.
S2 · 5–10	Evaluate Compare the three raw observations, means and ranges. Describe how surface flow carries the dye and why the score does not measure fat directly.

06 //

Discussion questions

1. What did the food coloring show after a soap touch?

SAMPLE ANSWERIt traced movement across the milk surface; our evidence is the direction and spread of the colored streaks and the recorded active-motion time.

2. How can we compare whole, 2% and skim milk fairly?

SAMPLE ANSWERUse equal shallow amounts, the same plate shape, dye drops, temperature and contact point, then compare the seconds of movement and 1–5 ratings.

3. Does a stronger swirl prove that sample has more fat?

SAMPLE ANSWERNo. The rating describes the observed pattern only. Soap amount, milk depth, temperature and plate conditions also affect it, so swirl intensity is not a direct fat measurement.

4. What is a limit of this demonstration as a model of cleaning?

SAMPLE ANSWERIt shows surface movement and interactions between soap and milk components. It does not test how well soap removes dirt from many surfaces or prove that new colored substances formed.

07 //

Common misconceptions

STUDENTS OFTEN SAY“The soap chemically changes the food coloring into new colors.”

BETTER IDEAThe dye is a tracer carried by moving liquid. This swirl does not show that a new colored substance formed.

STUDENTS OFTEN SAY“Whole milk always makes the strongest swirl because it has the most fat.”

BETTER IDEAFat content can influence the pattern, but plate shape, temperature and soap contact matter too. Compare repeat observations instead of choosing a guaranteed winner.

STUDENTS OFTEN SAY“The color shoots away because soap pushes dye molecules.”

BETTER IDEASoap changes surface tension and interacts with milk components; the resulting fluid motion carries the dye. The dye makes that motion visible.

08 //

Differentiation

SUPPORT

Use a photo card with one plate for each milk type and point to where the color first moves.
Offer intensity choices with picture anchors: 1 no streaking, 3 about one-third of the plate, 5 vigorous streaks across most of it.
Assign one student to touch the swab, one to time, and one to describe the pattern before swapping roles.

EXTEND

Keep whole milk fixed and compare a tiny versus a larger soap amount using fresh matched plates.
Use equal whole-milk samples at two temperatures and record both duration and intensity.
Repeat one milk condition three times and compare the ratings' range instead of selecting a single dramatic swirl.

09 //

Assessment rubric

Criterion	Beginning	Developing	Secure
Observation detail	Writes only “it moved.”	Names a color path or duration but leaves the milk condition unclear.	Records milk type, visible path and active-swirl time in seconds.
Classification	Uses no rating or changes the scale.	Rates the swirls but gives no shared meaning for a score.	Applies the same 1–5 anchors to whole, 2% and skim milk.
Explanation	Says the dye reacted or soap simply pushed color.	Mentions soap and movement without saying dye traces the flow.	Links soap's surface interaction to fluid motion that carries the dye, while avoiding a direct fat measurement claim.
Communication	Does not identify which milk was tested.	Shares a rating without describing the comparison conditions.	Uses the milk labels, rating scale and control observation to explain the comparison clearly.

10 //

Vocabulary

Surfactant – A substance such as dish soap that changes surface behavior and interacts with fats.
Surface tension – A property of a liquid surface that affects how it moves and holds together.
Emulsion – A mixture with tiny droplets of one liquid dispersed through another, as milk has fat droplets in water.

Tracer – A visible material used to show where a fluid moves.
Intensity scale – A set of shared score descriptions used to compare how strong an observation looks.
Control – A comparison condition, here a clean swab, used to notice motion without soap.

11 //

Safety, cleanup and troubleshooting

BEFORE STUDENTS TOUCH ANYTHING

Check for dairy or food-coloring allergies before setup. Do not drink or eat the milk after soap or test materials have touched it.
Wear eye protection. Use only one small drop of dish soap per test swab, keep it away from eyes, and wipe milk spills promptly to prevent a slippery surface.

Troubleshooting: If every plate looks similarly active, check whether the swab carried too much soap; the lesson notes that excess soap can hide differences. If dye spreads before the test, keep plates undisturbed after placing the drops and before the swab touches.