Mixtures & Solutions
Investigation 1
Part 2
Separating a Salt Solution
Students make another salt solution. They compare the mass of the mixture with the mass of its parts. Students evaporate the solution to separate its parts.
3. Lesson set up and Management
Changes in Systems (CH01 1.3.3)
• Know that matter can undergo changes of state such as evaporation, condensation, or freezing and thawing. Grades K, 1, 2, 3, 4, & 5.
• Understand physical and chemical changes at the particle level and know that matter is conserved. Grades 6, 7, & 8.
Evaporation can separate a liquid from a dissolved solid in a solution.
The mass of the parts of a solution add up to the total mass of the solution.
3. Lesson set up and Management
Materials:
If you did not make a packet as mentioned in the FAQ section, copy Handouts #4 and #5. Handout #4 should be done in class, and Handout #5 can be done as a homework assignment.
Set up materials stores with 4 containers of salt and 5 ml spoons for each container.
Set up 2-3 water containers.
Have a balance in each tub.
Add 2 evaporation trays to each tub.
Student Management:
Demonstrate to the students how to use a balance, as this may be their first exposure to balances.
Review the procedure on Handout #4 and explain the importance of careful measurement.
Have the students stop after Handout #4 and discuss what they have discovered.
Have them respond to the last question individually, in writing, and then discuss as a class.
Be sure to supervise the stacking, and make sure that the evaporation trays are labeled. Tell the students they will take a day or two to evaporate. Ask students what affects the rate of evaporation, to see if they know that the temperature of the room and the amount of liquid in the tray will affect the speed of evaporation.
When students examine the crystals, ask them how they know what they are looking at are salt crystals. Have some pictures from the web or a book showing the properties of a sodium chloride crystal. Explain that the solid form of a chemical is an identifying property.
Circulate and assess that the students are using the balance correctly.
Make sure students are using the minimum amount of solution to cover the evaporation trays. Otherwise, they will take a very long time to evaporate.
Use the response sheet as homework or in a writing workshop.
The concept of a solution being a mixture is difficult for students. Be sure to review their responses and clarify misconceptions.
Writing Support:
Have students write a journal entry about what they learned, and have them compare what they did in the last lesson (with the other two solids) to this experiment. Do a mini-lesson on summaries and conclusion writing in a writing workshop.
Reading Support:
Read "A Salty Story" in the Mixtures and Solutions: Science Stories book.