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.