Household pHun!

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Objective

Students will be able to analyze the property of pH in common household substances.

Big Idea

The students get an introduction to pH and identify common substances as acids and bases using red cabbage juice. Students love the bright colors of this lab!

Introduction and Connection to the NGSS and Common Core

In this lesson, students utilize text reading strategies to build their understanding of pH.  In addition, students test a variety of household substances to identify common acids and bases with red cabbage juice!

This lesson is designed to connect to the following NGSS and Common Core Standards:

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.

CCSS.ELA-LITERACY.RST.6-8.1  Cite specific textual evidence to support analysis of science and technical texts.

CCSS.ELA-LITERACY.WHST.6-8.9  Draw evidence from informational texts to support analysis, reflection, and research.

Science and Engineering Practices:

When using the text strategies utilized in this lesson, students think deeply about text in order to make their own conclusions and consider solutions to problems.  Students are using the scientific principle of Generating Questions and Designing Solutions, which states that, "Students at any grade level should be able to ask questions of each other about the texts they read, the features of the phenomena they observe, and the conclusions they draw from their models or scientific investigations." (SP1)   In addition, when utilizing text, students use strategies to obtain scientific information and evidence from text (SP8).  

Crosscutting Concepts:

When students use red cabbage juice on a variety of household substance, they begin to notice patterns both in which colors identify acids and bases, but in the types of materials that are acids and bases. For example, fruits are acidic.  Soaps or cleaning supplies tend to be bases. (Patterns)  Moreover, when students utilize text strategies, they generate thoughtful questions that take them "beyond the text" by making connections to the NGSS Cross Cutting Concepts as they read.  

Connecting to the Essential Question: What are you supposed to learn today?

5 minutes

Ask students, "What are you going to learn today?".  Students should respond by saying that they will be answering the Essential Question, "How do particles combine into new substances? And, what evidence can show how the physical and chemical properties of the substances change?"  This EQ is posted on my board and on the student's Chemistry Unit Plan

For a look at all the lessons that have led my students to this point and where we go from here check out the lessons in these units:

Physical Properties:  Molecular Arrangement and Phase Changes:  Focuses on Skills 1 - 4 of the Chemistry Unit Plan

This unit is designed to answer the Essential Question, "How do particles combine into new substances? What evidence can show how the physical and chemical properties of the substances change?" It particularly focuses on types of matter, physical properties, phase changes, and factors that affect physical properties. This unit's purpose is so much more than just the content, however. It's focus is scientific literacy. It stresses group discussion, discourse and utilizing text references when engaging in argument. Students utilize reading, writing, and speaking strategies in order to develop scientific literacy. It's scientific literacy immersion!

Chemical Properties and Reactions:  Focuses on Skills 4 - 6 of the Chemistry Unit Plan.

This unit is also designed to answer the Essential Question, "How do particles combine into new substances?  What evidence can show how the physical and chemical properties of the substances change?" This unit focuses on chemical properties and chemical reactions.  Students analyze evidence and property changes that allow them to distinguish between chemical and physical reactions.  In addition, students investigate the Law of Conservation of Mass as they look at how bonds are broken and formed in chemical reactions.  This unit is full of hands on labs and station rotations that will engage any middle school student in chemistry!

Mini Lesson: Talking to the Text About pH

25 minutes

Provide students with the Acids and Bases are Everywhere reading.  Ask students to "Talk to the Text" and work their way up the "Ladder of Discourse" as they interact with the text.  Students document their thinking as they read in the margins of the text and try to reach real discourse as they interact with the text.  

The levels of the "Ladder of Discourse" are "Tweets" (text to self connections), "Huh?'s"(questions or concepts they do not understand), "Found It" (finding answers to questions through context clues or finding science answers), and "Discourse" (combining ideas to think beyond the text).  

For more background on "Talking to the Text" and the "Ladder of Discourse" check out the following lessons.  These lessons include videos of me demonstrating these strategies and student work.

Talking to the Text:  Mystery Box Modeling:  Energy TransformationsHow does heat move?,Thermal Protection Systems

Ladder of Discourse:  Blow it Up With ButanePolymer PropertiesCrack that Marble LabRefracting TelescopesEngineering Earthquake Structures

I have also included a worksheet you could have your students complete as homework following the reading.  However, I would not give the students this worksheet while they read.  I have found that if students have a worksheet, they simply "hunt and peck" for answers instead of taking the time to think critically about the text as they are supposed with when "talking to the text".

 

As a class discuss the key points of the reading to make sure students were able to pull out the important information.  Some key points to discuss as a class are:

  1. The pH scale and the corresponding numbers for acids, bases, and neutral substances.
  2. What makes an acid an acid?  In upcoming lessons, it will be important that students recognize that when dissolved in water, acids have H+ (hydrogen) ions in them.  
  3. What are some common acids?
  4. What are some properties of acids?
  5. How can you determine the strength of an acid?
  6. What makes a base a base?  In upcoming lessons, it will be important that students recognize that when dissolved in water, acids have OH- (hydroxide) ions in them.
  7. What are some common bases?
  8. What are some properties of bases?
  9. How can you determine the strength of a base?
  10. What is a pH indicator?
  11. What happens when an acid and a base are mixed?  What are the products of this reaction?

One thing that I think is very beneficial at the end of this discussion is to list on the board a few chemical formulas such as HCl, H2SO4, NaCl, NaOH, and KOH.  Then ask students to predict which of those are acids and which are bases.  Hopefully students start to recognize that those substances with H in them are acids while those with OH in them are bases.  Even more, they can see that NaCl is neither an acid nor a base as it does not have either of those ions.

**A more detailed discussion of acid base reaction occurs in the next lesson.  This lesson is simply an introduction to acids, bases, and pH.

Household pHun Lab

45 minutes

Provide students with the Household pHun Lab.  Explain that they will be using cabbage juice as an indicator today as they identify common household substances as acids and bases. In order to do this, they need their own colored scale for comparison.  Then, project on the screen or provide colored copies of a cabbage juice pH scale.  Have the students color in each box on the lab sheet with the corresponding color using colored pencils, crayons, or markers.  

Making Cabbage Juice:

The day before, fill a large pot 3/4 full of water and bring to a boil.  Then break apart a red cabbage and put as many leaves in the pot as possible.  Allow the cabbage to cook for about an hour. (Turn on your kitchen fan. Cabbage is smelly!) Remove the cabbage leaves and allow the liquid to cool. Pour into a storage container refrigerate.  This makes a lot of cabbage juice.  I use this cabbage juice in upcoming lessons as well.  So, you will have a lot left over to use in the future!

Set Up:

Around the room set up 10 - 15 different household items.  At each station, mix the substances with water in a small beaker/cup with an eye dropper in the beaker. I typically go through about 100 mL of each mixture for 135 students. Leave the bottle/container of each substance next to the beaker to give the students a visual of what each substance is.  You may also want to label the beakers/cups.  Substances that I use include: laundry detergent, vinegar, milk of magnesia, ammonia, baking soda, apple juice, lemon juice, water, milk, Draino (Very Diluted!), citric acid, boric acid (can be found in pharmacies in the section for eye care), toothpaste juice (toothpaste mixed in water), dish soap juice, and pop.  There are so many more possibilities as well.  

 

Each group also needs a test tube rack that holds about 10 small test tubes.  I use small 5 mL test tubes so that I can cut down on the amount of materials used.  In addition, each group needs a cup of cabbage juice (I pre-pour the cabbage juice and the cups can be used for the entire day. I typically have about 10 groups per class. I pour 10 cups with about 100 mL of cabbage juice in each and that will last the whole day.)  With each cup, an eye dropper must be provided.  I happen to have two types of eye droppers, one that is long and translucent and one that is short with a black top.  I use two different types so that students can be clear about which eyedropper goes in which solution.  The short-black topped eye droppers go in the cabbage juice and the long, translucent eyedroppers go in the substances at the lab stations.  If you don't have two different types of eye droppers, label the eyedroppers for the cabbage juice so that it is clear.  

Lab Directions:

Explain to the students that every group is testing lemon juice, vinegar, baking soda, milk of magnesia, ammonia, orange juice and water.  Have them make predictions on the front of their lab sheet about whether these substances are acids, bases, or neutral.  Then, explain that students will also be testing a few more substances of their own choosing and have them make predictions for these as well.  What I tend to do for these "choice" substances is that I ask them to make predictions when they are at the station.  Students are not always sure about which "choice" solutions tol choose until they actually get to look over all of the stations.

Points to emphasize to the students about completing the lab include:

  • Each group of 2 - 3 will receive a test tube rack with test tubes.
  • Each group will receive a cup of cabbage juice and an eye dropper.  This eye dropper can ONLY go in the cabbage juice!  If a student places the cabbage juice eyedropper in any of the beakers at the lab stations, it will "contaminate" the entire solution.
  • The eyedroppers at each station can only go in those beakers.  Again, placing these eyedroppers in the cabbage juice or even in a different beaker will "contaminate" the entire sample.
  • The students must test the required substance, and then they can choose 5 or 6 others of their choice.
  • When they get to a station, they should:
    • Place one eyedropper full of the household substance in the test tube.
    • Place one eyedropper full of the cabbage juice in the test tube. 
    • Compare the color of the test tube to the cabbage juice scale on their lab sheet.
    • Write the name of the household substance next to the color that most closely matches the color of the test tube.

  • Students will not have one substance for every color.  And, they may write more than one household substance at a color.  
  • When they are finished with their tests, they must organize their test tubes in order of pH to create their own pH scale.

  • Before cleaning up, groups must come to the teacher and answer a series of questions about their test tubes.  This will be their assessment.  I post the questions on the overhead so that they know what they will have to answer.  Let them know that every member of the group will be asked to answer some of the questions. (This process is discussed with more detail in the "Closure" section of this lesson.)

Closure

5 minutes

Before cleaning up, groups must come to the teacher and answer a series of questions about their test tubes.  This is their assessment.  I post the questions on the overhead so that they know what they will have to answer.  Let them know that every member of the group will be asked to answer some of the questions.

Discussion Questions Include:  These questions along with the answers are included in the resource section.

  • Where are the test tubes that have hydroxide ions?
  • Where are the acids?
  • What ions are associated with acids?
  • Were there any test tubes that hold a neutral substance?
  • What would happen if you mixed a pink and green test tube together?
  • What is that type of reaction called?
  • What are the products of a neutralization reaction? (If they look stumped, have them reference their text.)

After answering the questions, tell them they can mix the test tubes together over the sink.  Have them wash out the test tubes and place the test tubes and cabbage juice on the back brown counter.