In this demonstration, students will determine the molarity of several different solutions demonstrated by the teacher.
By the end of this lesson, students should be able to
- determine the molarity of several different solutions.
This lesson supports students’ understanding of
- Mole concept
Teacher Preparation: 5 minutes
Lesson: 20 minutes
- One of each of the following:
- 2000-mL beaker
- 1000-mL beaker
- 500-mL beaker
- 250-mL beaker
- 100-mL beaker
- 3 plastic cutouts of moles
- There are no special safety considerations for this lab.
- Before the demonstration:
- Gather beakers all supplies listed above.
- You may also use stuffed moles or plastic moles instead of paper cutouts.
- Have students finish the prelab questions and discuss the answers.
- For the demonstration:
- Demonstrate the mole concept by placing one mole in the one liter beaker and add water to the 1L mark. Indicate that this is a 1 Molar solution.
- Then move the mole into each of the other beakers filled with water and ask the students what the molarity of the new solution is.
- I repeat for the 2 mole situation by asking first which size beaker would be needed in order to create a 1 molar solution using 2 moles of solute. Then complete the process for that row.
- Repeat this process again for the 3 mole row. Begin again by asking what size beaker would be needed in order to create a 1 molar solution using 3 moles of solute.
- Finally rip one mole in half and repeat the process by placing the half mole in each of the beakers.
- Optional: Demonstrate making a 1 molar solution of salt using the correct technique in a volumetric flask.
For the Student
- What is a mole? ____________________________________________________________
- What is the mass of a mole of oxygen atoms? _________________________________
- What is the mass of a mole of water molecules? _______________________________
- A 1 molar solution is one in which ____ mole of any substance is dissolved in enough water to make up a total of ____ liter of solution.
- Molarity is defined as “a unit of concentration used in chemistry to indicate how strong or weak a solution is”. Its symbol is ______ and its units are ____________________________________.
As you watch the demonstration, fill in the molarity of each solution when either 1, 2, 3, or ½ moles is added to each beaker.
# of Moles
- Circle the correct answer within the ( ) for each statement below.
- The higher the molarity, the (more concentrated … less concentrated) the solution.
- The lower the molarity, the (fewer … greater) the number of particles the solution.
- Describe two ways to make a 0.5 molar solution.