Writing Neutralization Reactions, Part 2

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Objective

Students will be able to write equations for balanced neutralization reactions.

Big Idea

Neutralization reactions occur when acids and bases are mixed. They produce a salt and water.

Introduction

In the previous lesson students were introduced to neutralization reactions. The objective of that lesson was that students would be able to write neutralization reactions given the acid and the base. This proved challenging because it had been a while since students had balanced chemical equations or balanced the charges in salts. In this lesson students will continue where they left off from that lesson, with the goal of improving their ability to write neutralization reactions.

This lesson, like the last one, aligns to the NGSS Practices of the Scientist of Developing and Using Models because the balanced chemical reaction is a written depiction of a chemical reaction. The process of using the equations to show what is happening in the test tube introduces a level of complexity beyond what students would observe from seeing color changes or even pH changes.

It aligns to the NGSS Crosscutting Concept of Cause and Effect in the sense that balanced chemical equations for neutralization reactions are best understood by examining the smaller scale mechanisms within the system—in this case the formation of a salt and water.

In terms of prior knowledge or skills, students should have a beginning understanding of how to balance charge, how to balance chemical reactions, and how to write neutralization reactions. However, if students are strong on these first two skills, then this lesson could be a stand-alone lesson on neutralization reactions.

There are no special materials needed for this lesson.

Do Now/Activator

10 minutes

Do Now: Students begin class with the task of comparing their exit ticket from the previous class with a partner to see if they can figure out what part of the problem created difficulty for them. (The exit ticket was to write the neutralization reaction for H3PO4 + NaOH).  I reason that this is a good way to start class because it provides students with the opportunity to delve right back into the material from the last class, which will be the topic for today’s class. It is also individualized; each student will have a conversation that relates to his or her own specific experience.

Activator: After students have had a chance to have this conversation, I ask them what they came up with. Some students report that they had no idea how to start the problem—it felt overwhelming. Others report that they are having trouble writing the formula for the salt, while still others complain of not remembering how to balance a chemical equation. I accept all answers, and explain that today’s class is designed to remedy some of these problems.

Mini-lesson

15 minutes

Mini-lesson: I begin the instruction portion of the lesson by handing out Notes for students. These notes are the key points that I made in the last lesson. After students have a copy, my lesson consists of pointing out the examples relate to the notes.

For Step 1, I trace the path of the arrows, showing how the acid and the base each contribute something to the salt, and to the water. For Step 2, I reiterate what is written, noting that balancing the charge is important. For Step 3 I re-teach the method students learned for balancing chemical equations.

This instructional choice reflects my desire to address some of the common concerns I encountered in the previous lesson. My hope is that through this lesson that at least some students are able to get unstuck and move forward to a place where they understand the material and now need to practice it. This will free me up to concentrate on fewer students who will need further explanation and re-teaching at a slower pace.

Application

25 minutes

Student Activity: During this portion of the lesson the classroom is a dynamic place. Some students work by themselves, some work with other students, and some get additional re-teaching from me. All students have been tasked with working on the neutralization_reactions_practice problem set II. I have posted this neutralization_reactions_practice II answer sheet in a few places around the room and I encourage students to check their work, but if they have a different answer than the answer key that they attempt to figure out why so that they can learn from their mistakes.

I have structured my lesson in this manner for a couple of reasons. First, I want students to make progress on the learning objective, but because students have different skill levels, the structure of this lesson allows for a lot of differentiation. Each student can enter into the work based on their own level of understanding. Second, this material, due to its multifaceted nature, provides multiple challenges for students. Students need time and multiple opportunities to work through these challenges.

Catch and Release Opportunities: As students complete the different sections of the practice problems, I stop class and ask a student to present a problem and talk through how they solved the problem.

Stopping class to discuss this is important for a few reasons. First, it gives students the chance to articulate their method, which improves the likelihood of deeper learning of the content. Second, it helps to break up the class. I make everyone stand up and come near the projector to hear the brief student presentation. In this way, I get everyone’s blood flowing, and break the class into small discrete units, which helps to reduce the tedious nature of the practice session.

Debrief

10 minutes

To wrap this lesson up I ask a student to walk through a final neutralization problem as shown in this debrief video. I am encouraged with the ease that he is able to do this. Still, I note that it will be important for students to work these problems, to make some mistakes, and to practice some more.

In this student work, for example, it is clear that there is a pretty strong understanding of the material. However, there are some mistakes in terms of balancing the charge on the salt and in balancing the entire chemical equation.