pHantastic Chemical Reactions Day 2

23 teachers like this lesson
Print Lesson

Objective

Students will be able to identify evidence that the chemical properties of the reactants and products are different in a chemical reaction and identify common acids and based by measuring pH using various indicators.

Big Idea

Students try to find an explanation when the teacher models a new medical innovation by revealing a "bloody" hand print! Students also create a rainbow of bubbles in a test tube, write a mystery message, and more during labs on chemical changes!

Introduction and Connection to the NGSS and Common Core

On Day 2 of this lesson, the teacher places her hand in a mystery medical solution and touches a piece of goldenrod paper to reveal a bloody hand print! The students then engage in a discussion in order to determine the cause of this unexplained phenomena.  Then, the students finish the pHantastic Chemical Reactions Lab Stations that they began in the previous lesson.  Last, students conclude the lesson using a vocabulary strategy called "Shape Vocabulary".  Be sure to check out the lesson for Day 1 of this activity.

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.6-8.3  Follow precisely a multistep procedure when carrying out experiments, taking measurements, or performing technical tasks.

CCSS.ELA-LITERACY.WHST.6-8.1.B  Support claim(s) with logical reasoning and relevant, accurate data and evidence that demonstrate an understanding of the topic or text, using credible sources.

CCSS.ELA-LITERACY.WHST.6-8.2    Write informative/explanatory texts, including the narration of historical events, scientific procedures/ experiments, or technical processes.

Science and Engineering Practices:

SP7  During their discussions about the "bloody hand print", students construct, use, and/or present an oral argument supported by empirical evidence and scientific reasoning to support or refute an explanation or a model for a phenomenon or a solution to a problem.  

SP8  In addition, in order to take part in this discussion, students gather, read, and synthesize information from multiple appropriate sources to develop their explanations. 

SP6  When writing their lab responses, students construct a scientific explanation based on valid and reliable evidence obtained from sources (including the students’ own experiments). 

Crosscutting Concepts:

In developing their ideas of what occurs during a chemical reaction, students note patterns in their observations that can serve as evidence of changes of chemical properties such as gas production, color change, temperature change, and pH change. (Patterns)

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

5 minutes

Ask students "What are you going to learn today?". Students should respond with the essential question that is posted on the board and in their Chemistry Unit Plan which is, "How do particles combine into new substances?  What evidence can show how the physical and chemical properties of the substances change?"

"What are you going to learn today?" is a strategy that I use on a daily basis with my students.  To see this strategy in action and to hear more about the benefits of this strategy, check out this video!

Ask students to get out their Chemistry Unit Plan and self assess where they believe their level of mastery on Skill 5, "I can provide evidence to show if a reaction is a chemical or physical change." At this point, students have already done this during a previous lesson.  This is an opportunity for them to make any changes if they feel that their level of mastery has grown.  My students rank themselves on a scale of 1 to 4 (4 being mastery).

Having students self assess is crucial to students becoming independent learners and developing a growth mindset.  In this video, you can see this strategy in action and hear some insight into how this has impacted my students' learning!

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!

Teacher Demonstration: Medical Advances - Extracting Blood Through Pores?

20 minutes

This demonstration elicits a big response from students!  In order for it to be effective, you have to sell it!  My school is near the University of Michigan.  I use this to connect my students to the story I am about to tell.  The story I tell unfolds something like this:

"Not only does the University of Michigan have an amazing medical department, but they also support and have a relationship with the local schools.  I am so excited to show you a new medical development today that I was able to obtain.  There are so many patients around the world that need blood; however, not everyone donates blood.  For many, they want to help, but they are scared of needles and the pain associated with giving blood.  Thus, there is a new solution that was developed."

I then pull out a container (big enough to fit my hand in) of the mystery solution.  The solution is water with a small amount of ammonia in it, but at this point the students believe it is the newly developed medical solution.  I then tape a piece of goldenrod paper on the board.  Goldenrod paper is a pH indicator.  It turns red in the presence of a base.  Then, I continue.

"This solution is able to relax the pores in your skin so that when you apply pressure on this paper, the blood is able to come through the pores without feeling any pain.  I am going to demonstrate this for you; however, if there is anyone that is squeamish around blood, I would ask that you take a step into the hallway and I will call you back in once I demonstrate. (This is important! This will look like real blood.  You don't want anyone fainting or getting sick!)"

I then stick my hand in the solution and let is soak for a second to build the suspense.  I then take my hand and "smash" it on the goldenrod paper.  Hold your hand on the paper for a second.  The students won't be able to see the red until you pull your hand away!

After the students react, many will raise their hands with questions!  Before even answering any of the questions, I say, "I hope you know that I would never actually extract blood from my hand in front of you."  I pause and give that statement a second to sink in.  I then say, "This solution is not actually a medical solution, it is a mix of ammonia and water.  Based solely on that knowledge, discuss in your groups what you think actually happened.  Remember when you are discussing that you should use the discussion sentence starters we have been working with and should reference text to back up your explanations."

In the resource section, I have included some of the text that students will use in their discussion that they have in their binders from previous lessons.  It is important to understand that students at their point have already gone through lessons about physical and chemical properties, evidence of chemical changespH, common acids and bases and discussion techniques.  

During this demonstration and throughout this entire lesson, I speak to students as if they are scientists and help them see what strategies scientists use to be successful.  This strategy, Target Language, helps students see themselves as scientists!  For more information about this strategy and actual footage of some of the phrases I use, check out this video!

pHantastic Chemical Reactions Lab Rotation

45 minutes

Have students continue with the lab stations that they began in the previous day's lesson.  Lab rotations are a great way to get students engaged and experience learning targets multiple times in one class period.  This video will provide you some insight into the many reasons I create lab rotations in every unit I create!

Remind students that goggles must be worn at all lab stations.  Although the chemicals being used at all of the stations are household items, they are acids and bases that can harm eyes and skin.  In addition, remind students to, "channel their inner scientist" as they carefully read the procedures in order to complete each station.

Before beginning the labs I also review the following criteria in lab writing and station work:

1.  Scientists back up their claims with evidence!  

     a.  For all of the questions that ask to provide evidence of a chemical change, students should also back up their claims with qualitative observations from the lab.  For example, it is not enough to simply say, "gas production".  Students should instead say something like, "There was gas production when bubbles formed in the bag."

     b.  For all questions asking to compare properties of the reactants to those of the products, students should include at least one changed physical and chemical property. I also emphasize that qualitative or quantitative evidence must be included.  Qualitative observations could come from what they observed during the lab or they could choose to pull quantitative data from the pHantastic Chemical Reactions Properties Descriptions text.  For example, in the pHantastic Chemical Reactions Properties Descriptions text for the Rainbow of Bubbles station, it states:

Reactants:  Ammonia is a liquid that has a pH of 11 and a boiling point of -33˚C.  Alka-Seltzer is a white solid that has a pH of about 9.

Products: Citric acid is a white powder with a pH of 2.  Water has a boiling point of 100˚C and a pH of 7.  Carbon dioxide is a colorless gas.

Thus, instead of writing "boiling point and pH" as their answer for a changed physical and chemical property, they should write, "The boiling point of a reactant began as -33˚C while the product finished with a boiling point of 100˚C.  The pH of the reactants were 11 and 9 while the pH of the product was 7 and 2."

2.  All lab questions for a finished lab station must be completed before rotating to the next station.  (I let my students rotate themselves as they finish as station work is something we do frequently.  You may want to rotate the groups on a timer if this is not the case for your students.)

pHun With Citric Acid

15 minutes

For more on the set up, materials, procedures and teacher tips for this station see the lesson for Day 1.  This section will take a look at student discussions and student work after completing the lab stations. 

The Reaction:

 

Student Discussion:

Here is a quick video of students identifying evidence as they observe this reaction.  Students get so excited during this station!

A Look at Student Work:

 

Notice that the student backed up each "sign of a chemical change" with an observation from the lab.  For example, instead of simply saying "gas production", she says "gas production because the bag expanded".  In addition, she notes all four signs observable at this station:  gas production, color change, temperature change, and pH change.

The student recognizes that it was an endothermic reaction because the surroundings became colder.  This indicates that energy is being transferred into the reaction.

Notice that this student responds with one physical and one chemical property that changed.  In addition, for each property she cites, she pulls data from the text to support her claim.  For example, she doesn't just say "the density changed".  She states, "According to the text, the density changed from 1.6 g/ml to 1.19 g/ml.".

Rainbow of Bubbles

15 minutes

This section takes a look at student discussions and student work after completing the lab stations described in day 1

The Reaction:

 

Student Discussion:

 Check out this video watching the reaction!  It's so cool!

 A Look at Student Work:

The student here identifies gas production, color change, and pH change as signs of a chemical change.  In addition, she provides qualitative observations from the lab to support her claim.  For example, she states, "the pH changed because the indicator turned colors."

The student notes one chemical property and one physical property.  She pulled these properties and the data to support it from the pHantastic Chemical Reactions Reactant and Product Property Description document.  She compares two data points for each property.  For example, she states, "According to the text, the boiling point changed from -33 C to 100 C."

Here the student notes that they are both liquids that are pH indicators.  However, she notes that they turn different colors in the same substances.  It is important for students to recognize that different pH indicators turn different colors.  Otherwise, they begin to say things like, "acid is red" which this is not true for every indicator.

Magic Writing

15 minutes

For more on the set up, materials, procedures and teacher tips for this station see the lesson for Day 1.  This section will take a look at student discussions and student work after completing the lab stations.  

The Reaction:

When phenolphthalein is sprayed with ammonia it turns bright pink!

When the message is sprayed with vinegar, the message disappears!

A Look at Student Work:

The student here explains that phenolphthalein is an indicator that turns pink in the presence of a base; and, thus, as the ammonia is a base, the message turned pink.  Many students here get confused and state that ammonia is an acid because they are used to cabbage juice turning pink or red in the presence of an acid.  You will need to touch base with students to make sure they are connecting to the idea that different indicators turn different colors.  Next, the student explains that when vinegar, an acid, is sprayed on the message, it disappears because it is neutralized and produces water.  One thing to look for in student responses is that they explain how the message was revealed and concealed.  Some students will explain how the message was revealed but forget to explain how the message disappeared.

This student cites one chemical property (pH) and one physical property (melting point) that changed as a result of this reaction.  It is important to note that she compares two data points for each giving evidence from the lab or the text as she compares the property before and after the reaction.

Aunt Acid....Way off base or the neutralizer?

15 minutes

For more on the set up, materials, procedures and teacher tips for this station see the lesson for Day 1.  This section will take a look at student discussions and student work after completing the lab stations.  

The Reaction:

Student Discussion:

 

A Look at Student Work:

The student correctly recognizes that there was gas production, color change, and pH change and thus is a chemical reaction.  In addition, she backs up each of these signs with observations from the lab that supports her claim.  Be aware:  Students will want to simply write, "Chemical. Gas production. Color change. pH change."  Backing up claims with evidence from the lab is key!

The student provides one chemical property (pH) and one physical property (state of matter).  In addition, she cites qualitative observations from the lab and the text to support her claim.

In this explanation, the student notes that there are acids in the stomach that can be neutralized when "eating" a base like an antacid.  She explains that the H+ and OH- bond to neutralize the stomach.  I would have loved for this student to have continued on to explain that when the ions bond, water is formed which has a pH of around 7.  This explanation will let you know if students really understand acid base reactions!

Conferencing in Small Groups

At the end of the first day, students completed this formative assessment as an exit ticket.  Before this lesson, I sort the exit tickets into stacks of similar learners, and on day 2 I meet with them.  This way, I address misconceptions with chemical reactions and neutralization before they complete all of the lab stations.  While the students work on the lab stations during this lesson, I meet and conference with these groups.

 When I sort these formative assessments, there are two specific groups of learners that I meet with.  First, there are those that are having a difficult time identifying all signs of a chemical change and backing it up with qualitative observations.  Second, there are groups that are still not clear about what occurs when an acid base reaction occurs.  When I call the groups over, I have them bring their working towards mastery lists so that they can graph their scores and update their lists of areas to work on.

Group 1:  Identifying Evidence

I call the students that struggled with the first question to a conference table and provide them with the student samples included in the resource section.  I have these three samples cut into slips and have the group organize the student work in order of "sounds like a scientist" to "sounds like a 7th grader".  I then have the students share why they made the decisions that they made.  Next, I ask them to place their own formative assessment writing "in order" where they feel it would fit.  Hopefully, students recognize that their work would could use some improvement when compared to the "anchor" or "sounds most like a scientist" paper.  What is important is that the students themselves identify what they need to improve on.  Students typically note the use of scientific vocabulary, including all of the signs of a chemical change, and backing up the evidence with qualitative observations.  Then, students update their Working Towards Mastery Lists.

In this video, you can see how using this strategy really makes learning visible for students.  Sorting student work is a great strategy that can be adapted to any learning target you have!

Group 2:  Acid Base Reactions

Conferencing with students based on formative assessment is one of the most effective strategies that I use in my classroom.  Watch student growth unfold in this video and hear more about why I use this strategy almost everyday!

For this group, I set out a series of cards that shows the reactants for HCl and NaOH reacting.

I first ask the students if they can "guess" which would be the acid and which would be the base.  Students should identify acids with the hydrogen (H+) ion and the base with the hydroxide ion (OH-).  I then ask them what occurs in a chemical reaction.  Students should explain that bonds are broken and formed.  Then, I show them a representation of the molecules in the reaction using mini marshmallows and toothpicks.  I break the bonds and show them the ions that are formed.

Then, I have the group make predictions about how these ions might "rearrange" to form new molecules.  They should recognize that the OH- and H+ will form water, which is neutral.  The remaining ions will form a salt.

Then, students update their Working Towards Mastery Lists.

Closure: Shape Vocabulary

10 minutes

At their table groups, have students complete "Shape Vocabulary" for the words acids and bases.  "Shape Vocabulary" is an activity in which students write the vocabulary word in the shape of its definition.  Thus, they will write the word "acid" and "base" so that it represents the definitions.  The students can draw pictures to aid their representations; however, the actual letters of the word should be written in the shape of the definition.  Have students at each table then share the decisions that they made in their representations. 

This video will be a great resource for you!  Not only do I explain the benefits of this strategy, but you will see students work through this process for yourself!

Acid:

This student recognized that acids have H+ ions.  Thus, they wrote the word acid to form H+.

This student was demonstrating where acids are found on the pH scale.

Bases:

This student recognized that bases have H+OH- ions.  Thus, they wrote the word base to form OH-.

This student was demonstrating where bases are found on the pH scale.

 pH Indicator:

This student wrote the word pH indicator in two different colors.  They showed hydrogen and hydroxide ions (acids and bases) pouring on the word causing the indicator to change color.