# The Ideal Gas Law and Dalton's Law of Partial Pressures

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## Objective

Student will be able to describe the relationship between variables in The Ideal Gas Law and Dalton's Law of Partial Pressures as well as solve problems using these gas laws as demonstrated by taking notes and performing practice questions.

#### Big Idea

The Ideal Gas Law describes the relationship between temperature, pressure, volume, and number of moles of a gas while Dalton's Law of Partial Pressures can be used to find the total pressure of a mixture of gases.

## Introduction

In this lesson students continue their learning about gas laws through reviewing Boyle's Law, Charles Law, Gay Lussac's Law, and The Combined Gas Laws and then learning about the Ideal Gas Law and Dalton's Law of Partial Pressures.

• This lesson does not align with any specific NGSS Performance Expectation; however, it does align with the old California State Standards.  Additionally, I feel that understanding gas laws and the basics of earth's atmosphere are important for students to know and is a topic that is interesting and fun for students.
• This lesson also aligns with the Next Generation Science and Engineering Practice 5: Using Mathematics and Computational Thinking. It does so because students are challenged to understand the mathematical relationship between variables (P, V, T & n) and solve problems using the Ideal Gas Law and Dalton's Law of Partial Pressures.
• This lesson aligns with the Next Generation Crosscutting Concept 3: Scale, Proportion, and Quantity.  It does so because students are challenged to think about gases, despite the fact that they cannot see them as well as understand how algebraic expressions can be used to understand the relationship between variables.

For this lesson I have students do a review activity using matching cards.  I print them on regular paper but you could also make them on cardstock to improve their longevity.

## Engage

15 minutes

To begin this lesson I have students spend some time reviewing what they have already learned in the first four lessons of the unit through performing a gas laws matching activity.

• The goal of this activity is to help students differentiate between the four gas laws (Boyle's, Charles', Gay Lussac's, and Combined) in terms of variables, constants, equation, type of relationship, and a representative graph.
• Before the lesson I make a set of cards for each table group (8 sets).  In order to make them I print out the attached papers(cards for gas laws matching 1 and cards for gas laws matching 2), cut out and then color.  I like to color each type of category card a different color.
• During the lesson I pass out a stack of cards to each group, making sure that they are shuffled.
• I then instruct students to, "With your group match each gas law with its characteristics.  You should have one of each colored card matched together.  Make sure to have them laid out on the table and when your group thinks that you are done than raise your hands for me to check."
• I then let students spend time working with their groups.  If they are stuck I tell them to go back and look at their old notes and foldable to help.
• Here is a movie showing my students working together to figure out which cards match.
• This picture shows the matched cards, notice how I have each outlined a different color.
• This movie explains how I make the cards and expect students to match them.

## Mid-Unit Quiz

15 minutes

After students have completed their introductory activity I then have them do a quick mid-unit quiz.

• The goal of this quiz is to check that students are understanding the material that we have covered so far in the unit.
• I have students put away everything except for their periodic table, a calculator, and a pen or pencil.  For this quiz they need their periodic tables because it has a reference sheet on the back that has the equations that they may need.
• I then pass out the quiz to students.  I have two versions of the quiz to ensure academic honesty and give them so that students have a different version from the person next to or across from them.   This is a copy of the quiz.
• As students complete their quizzes I have them turn over and then come around to collect.  I give students about 10 minutes to complete the quiz.  When students are done if I have collected their quiz then I encourage them to get out their binders and begin to get ready for the lesson.
• After class I grade the quizzes using the answer key and place in my gradebook.
• Then, the  next class period I pass back the quizzes and students do corrections.  See the attached reflection for more details about how I do quiz corrections.

## Explain/Elaborate

40 minutes

When students have completed their quizzes, I then let them know that we are going to be learning two more gas laws.

I pass out the Unit 7 lecture 4 students notes graphic organizer and show them the first slide of the PowerPoint.

• I begin the lesson with teaching students about the Ideal gas law on slide 2.
• I stress that this is the only gas law that has one of each variable at the SAME TIME!
• I also tell students that there are multiple "R" values, but that for this class we will only be using 0.0821 so our units for volume are always in Liters, temperature in Kelvin, moles in mol, and pressure in atm.
• I then have students do the practice questions on slides 3-9.
• I make sure that students use the problem solving technique of underlining what they know, circling what they want, labeling, writing down the equation, isolating their variable, and then solving for the answer.
• In the first example students have to first convert mL to L.  I have them do this to review this type of conversion.
• In the second example students need to first convert grams to moles using molar mass.  I give them the hint that they will need their periodic tables for this.
• I also teach students Dalton's Law of Partial Pressures which is on slide 10.
• I then have students do two practice questions on slides 11-14.
• For the first practice question students need to convert between pressure units.
• For the second practice question students get confused if they do not read the question carefully because they are solving for one of the partial pressures, not the total pressure.
• This is a copy of one student's filled in notes.

## Evaluate

20 minutes

To complete the lesson I have students perform practice homework questions on the Unit 7 lecture 4 homework paper.

I have students begin the homework in class and then finish at home.

I stamp their papers for completion at the next class period and go over the answer using the answer key.

Here is one example of a student's completed homework.

The biggest mistakes that students make are when they have to first perform a conversion before plugging into the equations.  For example in question 2 where they first need to convert pressure to atm, and in question 3 where they need to first solve for moles and then convert to grams.