Introduction to Solutions

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Objective

Students will be able to make solutions and analyze the solutions' concentrations both qualitatively and quantitatively through performing a lab activity.

Big Idea

Solutions are homogenous mixtures composed of solutes dissolved in solvents and can be analyzed both qualitatively and quantitatively.

Introduction

In this lesson students are introduced to solutions through performing a lab activity.  The goal of this lab activity is to give students a chance to make some solutions so that they have something visual to think about as we discuss solutions.  The goal is also to give students an overview of what we will be learning about pertaining 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.  For example students need to understand Molarity when discussing acids and bases, equilibrium reactions, and reaction rates. 
  • This lesson aligns with the Next Generation Science and Engineering Practice 3: Planning and Carrying Out Investigations.  It does so because students are performing a lab activity.
  • This lesson also aligns with the Next Generation Science and Engineering Practice 5: Using Mathematics and Computational Thinking.  It does so because students are using data from their lab to calculate the concentration of their solutions.
  • 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 there are several resources needed for each group:

  1. 1 test tube rack
  2. 4 test tubes labeled A, B, C, and D (I have these pre-labeled for students)
  3. 1 container of Koolaid (with sugar).  This must be bought fresh every year and replenished because it gets clumpy.
  4. 1 container of salt
  5. 1 bottle of water
  6. 1 scoopula (or you could have 2 so they don't cross-contaminate)
  7. 1 weighing boat (or you could have 2 so they don't cross-contaminate)
  8. 1 balance
  9. 1 stirring rod (or you could have 2 so they don't cross-contaminate)
  10. 1 25mL graduated cylinder

Explain

5 minutes

To begin this lesson I pass out the unit8 intro lab to students and have them quickly look over to themselves.

I then tell them, " We are going to be starting our new unit today which is all about water quality.  In order to learn about this we need to first understand what solutions are.  The goal of this lab activity will be to make some solutions and then analyze them both qualitatively and quantitatively."

I tell students that they are going to be making four solutions and that the instructions are clearly written for them on their papers.  I choose not to go over the details of the lab with students because this is fairly straightforward lab in terms of procedures that they should be able to figure out with their groups.  This practice helps students to become more independent in the lab.

I tell them that once they are in their groups to make sure follow the instructions and to keep their solutions until they are done with the entire lab.

I then break students into cooperative groups and have them start the lab.  See my reflection about cooperative groups for details on how I do this in my classroom.

Explore

50 minutes

In this section of the lesson students are actually performing the unit8 intro lab at their stations with their groups.  I tell them to make sure to use their calculators and that they will also need their periodic tables.

The students start by making four solutions (A-D). They then analyze the solutions both quantitatively and qualitatively by answering questions about them.  Although students have not seen the equations before for the quantitative part, I find that they are able to figure them out with their groups, and some additional help from me if needed.

As students work they make sure to take on their roles within their cooperative group.  This means that one student is keeping others on track, another student is reading the procedures and questions, a third student is doing the lab, and the fourth student is cleaning up.

Also as students work I walk around to make sure that the lab makes sense, check students answers, and keep students on track.

Here are some videos which show me doing this:

  • This first video shows me helping a group that is not sure how to figure out the solute and solvent in the solutions.  Notice that I have them go back to the definitions written on their paper to help them see how to find the answers.
  • This second video shows me helping a group which is not sure how to answer the question 3. When you were making the solutions, what did you notice as the solute dissolved in the solvent? What do you think is happening at the molecular level to allow this to occur? (if necessary draw a picture to explain).

Here are two examples of student's completed labs (lab 1 and lab 2 ) notice how the students explain their answers and shows their work for the math problems.

As students complete their labs I have them wash their test tubes out in the sink and work on their vocabulary that they received after the last exam.  This is an example of one student's completed vocabulary.

Evaluate

The nature of this lab is to allow students to begin to explore solutions so I do not grade it as a formal lab.  Rather, I grade this lab when I check their binders at the next binder check (at the end of this unit).  I grade based on 20 points and just take points off if they are missing sections.  For example if they only have half of the lab done they get 10 points.

Most of the students earn all of their points.  Those students who do not are usually missing the last part of their lab because they simply did not take the time to complete their analysis of the solutions in terms of concentrated/dilute or saturated/unsaturated/supersaturated.