Titration Part 2

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Objective

Students will build on their ability to solve titration problems.

Big Idea

The molarity of an unknown acid or a base can be determined using data from a titration.

Introduction

In the previous lesson students began to learn how to find an unknown concentration of an acid or a base using titration data. Exit tickets revealed that students ended the last class with varying degrees of skill at this task. Today’s class is designed for re-teaching of and practice in solving titration problems.

This lesson aligns to the NGSS Disciplinary Core Idea of HS-PS1-7: Use mathematical representations to support the claim that atoms, and therefore mass, are conserved during a chemical reaction. It does this because students balance chemical equations as part of their titration problems.

It aligns to the NGSS Practices of the Scientist of Using mathematics and computational thinking because students need to conduct a series of math-based steps in order to derive the unknown concentration.

It aligns to the NGSS Crosscutting Concept of Cause and Effect: Mechanism and Prediction because students will better understand the neutralization reaction (an effect) by examining what is happening at the molecular level.

In terms of prior knowledge or skills, students should have a basic understanding of the titration process.

There are no special materials needed for this lesson.

 

Do Now

10 minutes

Do Now: Students enter class and are asked to work the first problem of Titration Practice Problem Set II. While many students will not be able to work this problem to completion based on the exit tickets I saw from last class, I feel like this is a good way to start class because it gets students thinking about titration problems again, and it sends the message that I still expect students to meet this challenge. I give students several minutes to work on this problem.

 

Mini-lesson and Guided Practice

15 minutes

Mini-lesson: Today I co-teach my mini-lesson with a student, who takes the lead. My goal is to simply review how to solve titration problems that we began to learn how to do in yesterday’s class. This strategy is shown in this titration explanation video. The student does the teaching, and I ask clarifying questions that really tease out the details in the problem. For example, I might ask where the student got the volume of 0.02178 L of NaOH and she explains that you have to divide the 21.78 ml by 1,000 to convert the volume to liters, which is the unit used in the molarity unit.

My goal here is to diversify the teacher voice in my classroom, and to show students that a student has managed to learn the material well enough to teach it. This example of student progress is important because it shows all students that with effort and thought the material is accessible. 

Application

25 minutes

Student Activity: During this time students have a number of options depending on where they are in terms of understanding how to conduct titration problems.

Students who have limited understanding or who were absent yesterday can sign up for re-teaching. I work with those students first and basically deliver the same mini-lesson I did in the previous class.

Students who feel they understand the material are asked to practice, and to check their answers with the Titration Set II Answers that are posted on the wall around the room. If these students get a problem wrong, I ask that they try to figure out what they did wrong, and get help from another student before asking me for help. During this part of class I work the room and answer student questions in a manner that ensures that the student has to be an equal partner in figuring out their problem as modeled in this helping students video.

Toward the end of class students who have shown proficiency in solving problems are invited to take a titration quiz that shows they are able to solve titration problems. The quiz does not allow the use of notes and is taken independently. Students who get the quiz wrong are asked to reflect on their mistake and make a plan for avoiding the mistake in the future. When they can articulate their strategy they are given a different quiz. The answers to all the quizzes are found in this Titration quiz answer key.

Debrief

10 minutes

To wrap this lesson up I observe that about two thirds of students have been cleared to start the titration lab tomorrow. I congratulate these students. Here are samples of titration quizzes that students took. I note that students who have not yet passed the quiz need to do so before they can do the lab. I note that I am available after school today and during lunch if students want to get additional help, and I note that students can take the quiz before school tomorrow.

Based on my numbers, I anticipate that tomorrow I will first teach about the titration lab, and then I will release students to either do the lab or take the quiz and then do the lab.