##
* *Reflection: Developing a Conceptual Understanding
Solution Formation and Qualitative Description - Section 3: Explain

For some reason my students always have a hard time understanding solubility curves.

When I teach them this topic I make sure to go over the axis and what each line means in terms of saturation level of a solute at different temperatures.

In order to help students I always do a bunch of example questions, have students actually draw graphs, and even give students a visual of the process. This** **movie shows how I explain to students about solubility curves and how I try to help them visualize what it means to dissolve in 100grams of water by drawing on the board.

Despite these different ways of presenting solubility curves I still have many students who are confused on the topic. I think that for next year I will do one of two things.

- I will do a solubility curve lab such as this one, where each group will be assigned a different amount of a solute such as potassium nitrate, and then the whole classes data is pooled to come up with a solubility curve.
- I will skip this concept all together and just not teach solubility curves. I am already having to make decisions in terms of what to discard with NGSS, so if this is not a necessary topic, and I cannot do it justice than I may do better with just not teaching it.

*Developing a Conceptual Understanding: Helping Students Understand Solubility Curves*

# Solution Formation and Qualitative Description

Lesson 2 of 11

## Objective: Students will be able to explain what happens to make a solution and be able to describe solutions qualitatively through taking notes, performing practice questions, doing a computer simulation and watching videos.

In this lesson students learn about how solutions are formed and how to describe solutions qualitatively. This lesson builds on what they learned in the previous lesson, Introduction to Solutions.

- This lesson does not align with any specific performance expectations with the Next Generation Science Standards; however, it is imperative that students understand solutions before learning other concepts later in the year.

- This lesson aligns with the Next Generation Science and Engineering Practice 4:
*Analyzing and Interpreting Data.*It does so because students are learning how to analyze solutions qualitatively and how to interpret solubility curves.

- This lesson aligns with the
*Next Generation Crosscutting Concept 3: Scale, Proportion, and Quantity*. It does so because students are learning about solutions and how they are composed of different proportions of substances.

For this lesson the only special resource needed by students is access to computers for the PhET activity.

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#### Engage

*3 min*

To begin the lesson I remind students that we are beginning a new unit about water quality and that we are starting by talking about solutions.

I also tell them that, "As we discuss solutions today you should think back to the four solutions that we made last class period."

In order to help remind students I have a set of the four solutions at the front of the classroom.

#### Resources

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#### Explain

*40 min*

During this section of the lesson I teach students about solution formation, how to express solutions qualitatively, and how to read solubility curves. I present information on the PowerPoint while students take notes on their notes graphic organizer.

- I begin with explaining how to make a solution on slides 2-4.
- I then talk about how to describe solutions using the terms dilute and concentrated on slide 5.
- After this I talk about saturation level as a way to describe solutions on slide 6.
- On slides 7 and 8 I show students pictures of solutions that are unsaturated, saturated and supersaturated. I make sure to emphasize the idea that you can tell a solution is saturated by looking at it and seeing if there is any solute left at the bottom. I also emphasize that to make a supersaturated solution you must use heat and slowly cool the solution.
- After going through how to express solutions qualitatively I pause and have students think back to their Koolaid lab from the previous lesson. I hold up each of the four solutions and review whether they are dilute/concentrated or saturated/supersaturated/or unsaturated.
- This movie shows me doing this with my students.
- For the final part of the presentation I teach students about solubility curves and go through examples with them.
*For more details on this see my reflection on helping students to understand solubility curves.* - Here is a copy of a student's filled in notes.

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#### Elaborate

*30 min*

To help reinforce the idea of solutions and how to express solutions I have students perform a PhET computer simulation. The simulation is called concentration and is available online on the PhET website. The goal of the simulation is for students to understand how solute and solvent relate to the formation of solutions and solution concentration.

I pass out the phet lab paper to students and have them go up to a computer with their table groups.

As students are working I walk around to help make sure that they are all participating and to answer any questions that they may have.

Overall, this activity is fairly straightforward to students so they do a good job of being able to understand how various factors affect solution concentration.

This is an example of one student's completed lab. Notice how this student does not fully answer the questions for #4 and #5 in terms of WHY but then does so for the last few questions.

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#### Evaluate

*10 min*

To complete this lesson I have students do a homework. I have them start the homework at the end of class and then complete at home.

I stamp the homework for completion at the following class and then go over the answers using the answer key.

Here is a copy of one student's answers to the homework.

Some of the common mistakes by students include:

- letter e: knowing to multiply their answer by 2.
- letter f: knowing to divide the answer by 2.
- letter g: knowing to find the two values and then subtract.

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- UNIT 1: Unit 1: Working as a chemist
- UNIT 2: Unit 2: Matter, Atoms, and the Periodic Table
- UNIT 3: Unit 3: Bonding & Periodic Table Trends
- UNIT 4: Unit 5: Stoichiometry, Chemical Reactions, and First Semester Review
- UNIT 5: Unit 6: Energy
- UNIT 6: Unit 7: Earth's Atmosphere
- UNIT 7: Unit 8: Water Quality
- UNIT 8: Unit 9: Reaction Rates and Equilibrium
- UNIT 9: Unit 10: Nuclear Chemistry and Final Exam Review

- LESSON 1: Introduction to Solutions
- LESSON 2: Solution Formation and Qualitative Description
- LESSON 3: Factors that Affect Solution Formation
- LESSON 4: Expressing Solutions Quantitatively
- LESSON 5: Ice Cream Lab
- LESSON 6: Introduction to Acids and Bases
- LESSON 7: Acid and Base Calculations
- LESSON 8: Unit 8 Quantitative Review
- LESSON 9: Acid and Base Scientific Explanation Lab
- LESSON 10: Water Quality Testing
- LESSON 11: Unit 8 Review