Can You Judge a Powder by its Color?

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Objective

SWBAT make observations of powders and use the information to identify the composition of mixture of mystery powders

Big Idea

Can you identify each of the three white powders in a mystery mixture?

The Need for This Lesson

Middle school students seek relevance in their learning. We have been working on our observation skills as a chemist and will apply these skills by making observations about individual powders and applying those observation to identify which three powders make up a mystery mixture.

By applying their skills we can help students see the relevance of their learning. How might chemist apply their observations skills to determine what powders are used in the mystery mixture.

Investigation Preparation & Summary

20 minutes

Students make observations about various powders before and after combining them with various liquids to look for unique characteristics. (MS-PS1-2 Analyze and interpret data on the properties of substances before and after the substances interact to determine if a chemical reaction has occurred.)

Students apply their observations to determine which of the powders were used to make up the mystery powders. (SP4 Analyzing and Interpreting Data)

Their evidence is derived from their careful observations. (SP7 - Engaging in Argument from Evidence)

Here are links to the MSDS (Material Safety Data Sheets) for some of the materials students will be using in this lesson. I keep these handy and share with the school nurse just in case.

MSDS - Iodine

MSDS - Cornstarch

MSDS - Baking Powder

MSDS - Baby Powder

MSDS - Vinegar

Prepare the powder samples for each student group

  • Baking Soda
  • Baking Powder
  • Cornstarch
  • Baby Powder
  • Flour
  • Powdered Sugar

Create Mystery Mixtures for each student group

  • Mystery Mixture 1 - equal parts of corn starch, powdered sugar and flour
  • Mystery Mixture 2 - equal parts of baking soda, powdered sugar and flour
  • Mystery Mixture 3 - equal parts of baking soda, baby powder and flour

A complete materials list is available in the resources section.

This lesson was inspired by combining several similar lessons.

Students in Action

90 minutes

Day 1

In the following short video, I explain the strategies used at the start of a hands-on lesson. The strategies engage and focus students on the lesson.

 

I ask students to share their responses to the Turn/Talk/Record questions.

Take a look at the containers marked cornstarch and baking soda. Do not open the containers. Can you tell the difference between the two powders?  

Many students identify the baking soda as a brighter white than the corn starch. Some also note that the corn starch tends to be a bit clumpy.

These observation skills are great. 

If you cannot taste or touch the powders, how would you tell the difference? List as many ways as you can. (It is good to see some students have read ahead and identify wafting as a possible way to distinguish powders.)

You cannot touch or taste the powders in this exploration. You can smell them. The proper technique to smell chemicals is to cup your hand above the container and waft, carry gently through the air, toward your face. You should not breathe in the air through your nose. Just bring it close enough to smell. Pretend that someone wants you to smell milk to decide if it is sour or not. Open the baby powder container and practice wafting. In addition they identify color and whether the powder appears to be a different shade of white or if it clumps together. 

Students have six different powders at their desk to evaluate. Each of the powders are named. I ask students to complete all the observations with the exception of heat for each powder. Powders are described, mixed with water, vinegar and Iodine. They examine the powders on a sheet of wax paper.

 

When they have finished all the non-heat observations, we remove the wax paper for safety before lighting the tea candle.

Students finish the individual powder observations on Day 1. Student samples from day 1 show that they have made solid observations. Each powder exhibits a pattern of responses to the tests. These patterns are used to answer the challenge questions on Day 2 - What powders are in a mixture?

Full Size Student Sample in Resources

Day 2

On day 2 students are given three containers labeled Mystery Powder 1, Mystery Powder 2 and Mystery Powder 3. Students conduct the same tests on the mixtures as they did on the solids, completing all parts of the observation chart except the heat test. Once again the heat tests are conducted when the wax paper has been removed. 

  

Full Size Student Sample in Resources     

When students finish their observations, they compare the patterns observed for each of the individual powder responses and use that data to evaluate the mixture. 

Connecting the Learning

5 minutes

When students finish their evaluations of the powders we have the great reveal. 

Mystery Powder 1 - Flour, corn starch and powdered sugar

How do we know? The flour smells like burnt toast when heated. The corn starch turns black when mixed with Iodine, there is no reaction to the vinegar, no smell of baby powder and the heat mixture bubbled quickly so the students conclude the second powder is powdered sugar and the third powder is corn starch.

Mystery Powder 2 - Flour, baking soda and powdered sugar

How do we know? The flour smells like burnt toast when heated. Baking soda is identified because of the reaction with vinegar. When heated the powdered sugar bubbles so students conclude powdered sugar is also in this mixture.

Mystery Powder 3 - Flour, baking soda and baby powder

How do we know? The baby powder is one of the most obvious first observations when wafting the powder. Again the flour smells like burnt toast when heated. Baking soda is identified because of the reaction with vinegar.

These observations represent a composite of ideas from the class.