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Applying the Scientific Method to Stain Removal (15 Favorites)

LAB in Observations, Introduction, Lab Safety, Scientific Method, Graphing, Experimental Design. Last updated June 28, 2021.


Summary

In this lab, students will explore the real scientific process by designing an experiment to solve a problem. Students will learn about basic lab equipment, safety, and the scientific process of trial and error while solving a common problem: What color of food coloring requires the most bleach to remove?

Grade Level

Middle or High School

NGSS Alignment

This lab will help prepare your students to meet the performance expectations in the following standards:

  • MS-ETS1-1: Analyze data from tests to determine similarities and differences among several design solutions to identify the best characteristics of each that can be combined into a new solution to better meet the criteria for success.
  • HS-ETS1-2: Design a solution to a complex real-world problem by breaking it down into small, more manageable problems that can be solved through engineering.
  • HS-ETS1-3: Evaluate a solution to a complex real-world problem based on prioritized criteria and trade-offs that account for a range of constraints, including cost, safety, reliability, and aesthetics as well as possible social, cultural, and environmental impacts.
  • Scientific and Engineering Practices:
    • Analyzing and Interpreting Data
    • Planning and Carrying Out Investigations

Objectives

By the end of this lab, students should be able to

  • Write a testable hypothesis.
  • Design a basic experiment using proper lab equipment and techniques.
  • Outline the steps of the scientific method and explain the purpose of each.
  • Construct proper data tables and graphs for an experiment.
  • Evaluate evidence from an experiment to make a claim.
  • Communicate their results in both lab report and oral presentations.

Chemistry Topics

This lab supports students’ understanding of

  • Scientific Method
  • Experimental Design
  • Lab safety
  • Lab equipment
  • Observations
  • Data Collection
  • Graphing

Time

Teacher Preparation: 15 minutes
Lesson: 90 minutes for lab; 15 -30 minutes for presentations depending on size of class

Materials (1 of each item per lab group)

  • 10 mL Graduated cylinder
  • 100 mL Graduated cylinder
  • 50 mL Graduated cylinder
  • Beaker
  • Bleach
  • Erlenmeyer flask
  • Food coloring (red, yellow, green, blue)
  • Goggles
  • Plastic pipettes
  • Rubber stopper
  • Soap Sponge (cleanup only- not used for placing dye on and testing)
  • Spot plate
  • Stirring rod
  • Test tube
  • Test tube brush
  • Test tube rack
  • Thermometer
  • Toothpicks
  • Water

Note: the size of the glassware doesn’t matter, whatever your lab has available will work

Safety

  • Always wear safety goggles when handling chemicals in the lab.
  • Students should wash their hands thoroughly before leaving the lab.
  • When students complete the lab, instruct them how to clean up their materials and dispose of any chemicals.
  • Review the SDS for Bleach (Sodium Hypochlorite Solution).
  • Use caution when working with bleach. Wear gloves. A fume hood should be made available.
  • When working with acids, if any solution gets on students’ skin, they should immediately alert you and thoroughly flush their skin with water.
  • When diluting acids, always add acid to water.
  • Do not consume lab solutions, even if they’re otherwise edible products.

Teacher Notes

  • This activity is meant for students to learn about the scientific method through trial and error and works best at the beginning of the year as the first lab you have students complete. 
  • Students are only testing the reaction between the bleach and the dye, no materials or cloths are needed to perform the test on, that will just add another variable that students don’t need to consider in order to solve the problem.
  • The hardest part as a teacher is not correcting original misconceptions. Only intervene in student decisions if student safety is an issue. Sign off on methods before students begin testing to ensure their safety.
  • The activity works best with students working in pairs or at maximum groups of three.
  • To make it easier, place all available materials at a central location in the lab so that students have to make decisions and so that they are not crowded with materials that may get broken.
  • If a group solves the problem quickly on the first try, you can ask those students to come up with a second method to test. Students must learn that it is okay to be wrong as long as they learn from their mistakes.
  • Many students will make decisions in their methods that you know will take large amounts of chemicals. Students must learn from their own mistakes, and learn to solve the problem themselves.  
  • This problem can be solved with as little as 20 drops of bleach total if students decide to use a sample of diluted bleach, and using only one drop of dye initially.
  • In my experience, on average most students will need about 50 drops total to complete their final trial. I suggest having 1 gallon of bleach available per class. Depending on the skill level of class and the number of trials you allow, you may use much less than this amount.
  • I encourage teachers to complete a few trials in order to observe results first-hand, in advance of doing the lab with their students.
  • Students commonly will test amount of dye to start with, amount of water to add, diluting and then removing small samples to test, method of adding bleach- mL versus drops. Allow students to make their own decisions and then make changes as they learn their methods weren’t perfect.
  • If you want this to feel more like a competition to motivate students to get the best methods, you can post results of final total amount of bleach used by groups for their best trial. 
  • A rubric has been provided as an example for optional use, to help assess the different components of this lab. Points should be adjusted based on the grading scale for your class.
  • The presentation portion of this lab can be made to be an optional activity, depending on class time available.

For the Student

Lesson

Background

The scientific method is a set of steps that scientists can utilize to help solve problems and test ideas. During the following inquiry lab, you will be exploring these steps while solving a real-world problem: What color of food coloring is the hardest to remove with bleach?

Scientific Method Step 1: Observation/Research Question

The scientific method begins with a testable observation or question about something you notice in the real world. Today’s research question has been provided for you:

How much bleach should be used to remove stains of different colors?

Your Role: You are a Product Design Engineer & Manufacturing (your job is to create the labels that indicate how much bleach should be used when you wash your clothes).

Step 2: Create a Testable Hypothesis 

A hypothesis is an educated guess about the outcome of your experiment.

  • It must be testable and not an opinion that can’t be proven.
  • A proper hypothesis contains the independent and dependent variables in your experiment, as well as justification based on research and/or prior knowledge. 
  • The independent variable is the one thing you will physically be changing from one trial of your experiment to the other. You are trying to determine its effect. 
  • The dependent variable on the other hand is the variable you collect data about during your experiment. 
  • All other variables in your experiment must be held constant, meaning that they must not be altered from one trial to the next. 
  • A hypothesis should be written in the following format:
    • If independent variable prediction, then dependent variable prediction.
  • The hypothesis for this experiment has been started for you, fill in the blanks with your predictions.

State the independent variable: _________________________

State the dependent variable: ___________________________

Hypothesis: If the stain is _____________ in color, then it will take the ____________ (more/less) bleach to remove it, because ___________________________________.

Step 3: Performing an Experiment

Safety

  • Always wear safety goggles when handling chemicals in the lab.
  • Wash your hands thoroughly before leaving the lab.
  • Follow the teacher’s instructions for cleanup of materials and disposal of chemicals.
  • When working with acids and bases, if any solution gets on your skin immediately rinse the area with water.
  • Do not consume lab solutions, even if they’re otherwise edible products.
  • Food in the lab should be considered a chemical not for consumption.

Materials

  • You may choose to use any of the following materials to design your experiment. 
  • Remember, when completing an experiment try to use as little consumable products as possible. Consumable products are those that you would have to purchase to keep retesting. Companies make more money when they can solve problems cheaply
  • Just because an object is listed does not make it a good choice to use. Begin by determining the purpose for each material in the experiment.
10 mL Graduated cylinder
100 mL Graduated cylinder
50 mL Graduated cylinder
Beaker Bleach
Erlenmeyer flask
Food coloring (red, yellow, green, blue)
Goggles
Plastic pipettes
Rubber stopper
Soap & Sponge
Spot plate
Stirring rod
Test tube
Test tube brush
Test tube rack
Thermometer
Toothpicks
Water

Purpose of each selected material item:

  • In the space below, list and describe the purpose of each item you will use in the experiment.
  • Also, indicate the quantity of each item needed.

Method

As the research team, you must come up with a series of steps to complete your research task (this may be completely different than other groups around you. There is more than one correct way to complete this task!) In the space below, list the steps in chronological order and be sure to include the name of the pieces of lab equipment you are using. Your method must be signed off on prior to getting to start testing.

*Remember your goal is to solve the problem using the least amount of consumables (food coloring and bleach) possible.


Teacher Initials required to begin testing: ______

Collecting Data

  • Complete your design experiment.
  • Scientists do not always come up with the best way of testing their materials on the first try. If you get started, and find that there is probably a faster and cheaper way of testing then you may change your design of the experiment. You will need to clear this change with the teacher before proceeding.
  • You must create a labeled data table in the space below to collect results. 

Step 4: Analyzing Data & Drawing a Conclusion

When an experiment is complete, scientists must analyze their data. Data is often best understood when you use visual aids like graphs. For this experiment, you are to create a graph.

  • A proper graph includes the independent variable on the x-axis, the dependent variable on the y-axis, labels of units, even spacing of the axis, and a title.
  • Create a graph on a sheet of paper or white board that will later be used to present your results.

After your graph is completed, analyze your results. Was your original hypothesis correct?

Conclusion

Write at least one complete sentence to summarize the results of your experiment and to answer the original question posed.

Step 5: Publish your results

Publishing your results is important in the scientific community. It is a way for other scientists to learn and make sure that experiments were performed accurately. Scientists publish results in lab reports, scientific journals, and present their findings to others at symposiums and conferences. 

In addition to creating a published work (this lab report) to share with the scientific community (the class), you will be asked to speak at a symposium (science conference) discussing the topic. In your presentation, you must discuss the following:

  • Your original hypothesis
  • How you tested the project (what materials did you use and what were your basic steps?)
  • Your conclusion (answer the question: what color required the most bleach?)
    • Use your graph to help others visualize your results.
  • What would you do differently the next time around? What further questions you would want to study?
  • Each member in your group will be required to speak in order to get full credit for your presentation.