• Monitor student involvement and note taking during the presentation.
• Provide feedback during group work and practice problems to assess general understanding of terms and use of formulas.
• Collect Concentrations Worksheet for individual assessment.

Prior to the lesson, mix together two different containers of a powdered drink mix. Follow the directions for the first batch and double the solute ingredients for the second batch. Note: Ask students if they have any food allergies and read off the ingredients, if needed. Give students a small sample of each drink and ask the following questions:

• “Which drink tastes stronger?” (the more concentrated drink)
• “What is the solute and solvent in this solution?” (solute: powdered mix, solvent: water)
• “Which drink has more solute in the solution?” (the more concentrated drink)
• “Which drink has a higher concentration of solute?” (the more concentrated drink)

Use the last question as a tie-in to the lesson. Tell students the concentration of a solution refers to the amount of solute dissolved into a specific amount of solution. “Can anyone tell me some different ways the concentration of a solution could be expressed?” Collect student responses and ask guided questions as they respond. (Examples may include parts per hundred, percentage of solute in a solution, parts per million, etc.) Tell them there are several ways to express the concentration of a solution, but they are going to learn about three:

• molarity
• molality
• percent by mass

“We will concentrate mainly on mass percentage, but we will learn the basics of molarity and molality.” For a refresher on the concept of the mole, please refer to the following video: http://www.learner.org/vod/vod_window.html?pid=803.

Show the class the Concentrations PowerPoint Presentation (S-C-9-3_Concentrations Presentation PowerPoint.pptx). Either project the presentation with a document camera or LCD projector or print copies of the PDF version for each student (S-C-9-3_Concentrations Presentation PDF.pdf).

Instruct students to take notes throughout the presentation and write down questions they have. When finished with the presentation, address student questions before moving on.

Hand out the Concentrations Worksheet (S-C-9-3_Concentrations Worksheet and KEY.doc). Say, “Let’s go over the first problem as a class and then you and a partner can work on the remainder of the first page together. You complete the second page independently.” Write the following problem on the board and have students follow along on their worksheets. Ask guiding questions throughout each step.

Example Problem

What is the percent concentration of the following solution?

14g of sucrose dissolved in 183 g of water

Explanation of Answer:

• The formula for percent concentration is the mass of the solute divided by the mass of the solution times 100.

• The mass of the solute is 14 g of sucrose and the mass of the solvent is 183 g. Solvent isn’t listed in the formula but solution is. What is the formula for figuring out the solution? (solute + solvent = solution so 14 g + 183 g = 197 g of solution.)
• Plug the solute and solution amounts into the formula for percent composition and solve.

This worksheet may be given as homework if class time runs out. Collect when finished, and address student questions as needed.

Extension:

• Students requiring further practice can use a partially completed concentrations worksheet to address specific student modifications. This modified worksheet can be shortened or filled in with steps to lead students toward the right direction in solving for the unknown variable.
• Students performing beyond the standards can research global climate changes and the potential impact on marine life. Students must present an argument in essay form accompanied by a visual representation (PowerPoint, poster, oral, etc.). Students should address specific species and their dissolved oxygen requirement and the effect rising temperatures are having on their survival.