Mystery Powders

Show students the jar filled with the mystery powder (baking soda or powder). Tell them that you are unsure of what this powder is and you need their help to figure it out.

Ask students to suggest ways to determine what kind of powder it is. Students may make suggestions such as feel it, taste it, smell it, or look at it up close. Pass the jar around so that students can take a closer look at the powder.

Remind students that when they are using their senses to gain information, they are using the skill of observation.

Have students make observations of the powder and record them on the board or a sheet of paper under the headline “Observations”.

Ask students to predict what they think will happen if vinegar is added to the powder. Make notes of students' predictions on the board or a sheet of paper under the headline “Predictions”.

Language

Consider creating a word wall of terminology that students will encounter over the course of this lesson such as powder, grainy, coarse, smooth, matte, shiny, rough, bubbles, gas, independent variable, controlled variable, dependent variable, etc.

Safety

Remind students to never put anything in their mouths, to smell, or to touch, unless told it is safe to do so by a trusted adult. In science we do not use our senses of taste, touch or smell to make observations unless we know it is safe to do so.

Idea

If it is conducive to your classroom you could have students use their sense of taste if they wish, provided there are no allergies to any of the powders. All of these suggested powders from the materials are safe for ingesting.

Explain or review the concept of a fair test (also known as a controlled experiment) with students.

In a fair test, only one thing (the independent variable) is changed at a time. Everything else (the controlled variables) are kept the same. That way, only the independent variable leads to the results (dependent variable). Explain that in the test you are doing, and in the testing they will do, only the powder will be changed. The volume of liquids and solids, the type of liquid, the length of time stirring, will remain the same for each.

Carefully measure out 1 tsp of the mystery powder into a small cup or dish. Then measure and add 1 tsp of vinegar to the powder. Have students closely observe as you mix the two together.

Ask students to describe what they have observed and write these new observations on the board or a sheet of paper under the heading “Results”

Now tell students that they will be conducting their own fair test with the powders. Explain to students they are matching up the physical properties and chemical reaction of the known powders to the "mystery" one. It is up to them to see if they can discover which of their powders is the mystery powder in the jar.

Arrange students in groups of 4-5.

Provide each group with 1 bag of each of the labeled white powders and with the Mystery Powder Predict and Observe Chart reproducible [Google doc] [Word doc] [PDF].

Note: Modify the chart to reflect the powders that the class will be testing.

Have the students delegate the tasks in their group (e.g., one person is the note taker, another person can measure out the vinegar, another can add the vinegar to the powder, etc.). Students can take turns doing these tasks.

Explain the instructions to students. You could do this by providing each group with the Mystery Powder Fair Test Task Card reproducible [Google doc] [Word doc] [PDF] or projecting the page digitally on a screen.

Review each of the steps with students to ensure that they understand each step. 

Note: Below are some examples of powders mixed with vinegar for your reference.

Observe students’ interactions with the materials and the fair testing process, and document observations, including discussions and questions raised, to determine the direction of future learning.

Facilitate discussion with students about their findings and how the information gathered can be used to determine what is in the “mystery powder.”

Nature of Science

Scientists do not work alone. They work on teams where different members bring different skills and abilities to the task they are working on.

Language

Review what a prediction is to ensure students understand the concept before beginning the activity. Suggested prompts can include:

• “What do you think a prediction is?”
• “How do we make predictions?”
• “Why is it important to make a prediction?”
• “When do we make predictions?”

Safety

Remind students to never put anything in their mouths unless told it is safe to do so by a trusted adult.

Images and Videos

Adapt the Mystery Powder Predict and Observe Chart reproducible to include the powders that the students will be using.

Nature of Science

Students use the Computational Thinking Skills of pattern recognition and logical thinking as they work to determine how each powder is like or unlike the mystery powder.

Conduct a poll to have students vote on which powder they think is the mystery powder. You could do this by a show of hands, using a digital program (e.g., Poll Everywhere, Plickers, etc.) or on chart paper.

At the end look at what the most common prediction was and ask the class if they agree. Ask students to explain their reasoning. Reveal to them what the mystery powder was (baking soda or baking powder).

Idea

For a no tech option, have the powder names written on the board and give students a sticky note, chalk or marker and leave a mark under the powder they want to vote for.

Nature of Science

This sharing of results and conclusions is analogous to what scientists do. Sometimes results are shared with small groups, at conferences, etc. Feedback could send them back to the lab to do more research or might help them clarify their thinking. The final step is usually that results are published in a magazine for more scientists to learn from the work they did.

The final task will draw on students' prior knowledge of physical and chemical changes. If students are familiar with the topic, go on to the last step of these instructions.

If students are not familiar with the topic of physical and chemical changes you could activate their prior knowledge by asking discussion questions and recording student answers or showing them the Physical and Chemical Changes interactive presentation [html] [Google slides] [pptx] [PDF].

In addition, seeding some photo examples might be helpful for students.

Have conversations with students about the differences between physical and chemical changes.

Discussions

Discussion prompts can include:

• “How do we know the difference between a physical change or a chemical change?”
• “What causes physical changes?”
• "What causes chemical changes?"

After students have reviewed information relating to physical and chemical changes, you could have them complete the Physical or Chemical Change Identification Chart reproducible [Google doc] [Word doc] [PDF] either individually, in small groups, or as a class.

Note: Modify the chart to reflect the powders that the class will be testing.

Students could hand in the completed reproducible which could be used as an assessment of learning.

For reference:

• Vinegar + granulated sugar = physical change (sugar does not dissolve completely in vinegar which is a weak acid. Vinegar is mostly water and sugar does dissolve in water.)
• Vinegar + icing sugar = physical change (icing sugar does not dissolve completely - like granulated sugar.)
• Vinegar + cornstarch = physical change (the cornstarch forms a cloudy solution - it does not dissolve or react with the vinegar)
• Vinegar + baking soda = chemical change (bubbles are formed which indicates that a gas is produced)
• Vinegar + baking powder = chemical change (bubbles are formed which indicates that a gas is produced - baking powder contains baking soda and a dry acid)
• Vinegar + powdered milk = chemical change (precipitate forms; these are observable as clumps with a gooey texture)

Idea

The Physical or Chemical Change Identification chart could be completed by asking students to raise their hands for each powder.