The Case of the Missing Secret Message

8 teachers like this lesson
Print Lesson


SWBAT read a fictional science mystery to observe how acid/base chemistry can be used to create "invisible ink." SWBAT perform an experiment and use deductive reasoning to solve the mystery.

Big Idea

Who did it? Solve the mystery by applying knowledge of acids and bases. Students investigate by creating "invisible ink," making observations, and writing a conclusion.

Before Reading

5 minutes

Before Reading

To get students engaged and thinking about acids and bases, I ask them to read the background information on the Worksheet - The Case of the Secret Message to learn about the pH Scale. Reading the background paragraph will spark questions (SP#1) and comments that students can share with their peers. Students take one minute to read, then share share their thoughts, questions, and/or comments with their partner(s). Providing time to process information and discuss thinking is best practice and beneficial to the learning experience. Some terms students should use in their discussion include: acids, bases, the pH scale, and a neutral solution. As students read and discuss, I circulate the classroom to listen to their conversations, encourage their use of domain-specific vocabulary, and take time to clarify any misconceptions.

Read: The Case of the Secret Message

10 minutes

The Case of the Secret Message

The Reader's Theater, "The Case of the Secret Message" comes from SuperScience, April 2010, p 4-5.  A Reader's Theater is a way to be involved in an oral reading which combines reading practice and performing. Before reading this aloud with the class, I choose student parts for the reading with popsicle sticks. This strategy is an unbiased method for recruiting students to be readers. Then provide one copy of the Reader's Theater to each student so that they can follow along.

This Reader's Theater is a story about a middle school science class investigating acids and bases. Students solve the mystery after the reading.

For more information on a Reader’s Theater, go to Reader's Theater: Giving Students a Reason to Read Aloud.

After Reading

5 minutes

After Reading

Student groups work together to answer questions that lead them to solve the mystery. These questions scaffold the learning and require students to know physical and chemical characteristics of acids and bases and to apply that knowledge to the mystery. Students could identify characteristics such as: acids taste sour, bases taste bitter, and/or bases feel slippery. Students will (RST.6-8.1) determine the conclusion of a text "Who is the culprit? How do you know?"

After students have an opportunity to write their answers, I use popsicle sticks to draw students into the discussion. This gives me a chance to listen and learn if there are any misconceptions about acids, bases, or the mystery. As I facilitate a whole class discussion, students are answering the questions: "Who is the culprit? How do you know?" Students use evidence from the reading to justify their answers.

Solve The Mystery: An Inquiry

15 minutes

Solve The Mystery

Students get a chance to make the mystery authentic. I provide supplies, let students read the directions, and then work independently with their partner(s) to (SP#3) carry out an investigation and recreate the "secret message." Students will (RST.6-8.3) follow precisely a multistep procedure when carrying out this investigation. This is a time of discovery for students as they learn how acids and bases interact and deepen their understanding of the characteristics of acids and bases. The inquiry makes acids and bases real and authentic.

Students use the supplies to write the secret message. I provide hair dryers to speed up the drying process so that students will finish during the allotted class period.


5 minutes


Now, let's write a conclusion. As with any inquiry, sometimes it works and sometimes it doesn't, but that ok. This provides opportunity to discuss what went right, what went wrong, and changes that could be made to the inquiry. This step is very important for students to "come full circle."

I have learned that you need to take students back to the questions so they can think about the process. "Who wrote the hidden message? What did you learn about acids and bases?"  Take 2 minutes for students to process the questions and write a conclusion. I give them a sentence starter to help with the process, for example:  I learned that . . .because. . .  Finally, take 2 minutes to share answers with the class so students can hear other student thoughts.

Some students wrote:

  • I learned that acids and bases create a reaction when put together because grape juice (acid) and baking soda (base) can react to reveal a secret message.
  • I learned that two bases together or two acids together will have no reaction because they are the same so nothing can happen.
  • I learned that acids and bases can reveal a message because they react with each other.