Mixtures & Solutions
Investigation 2
Part 1
Salt Saturation
Students make a saturated salt solution. They discover the amount of salt needed to saturate the water using the property of mass.
3. Lesson set up and Management
Properties of Substances (PR01 1.1.1)
- Use properties to sort natural and manufactured materials and objects, for example, size, weight, shape, color, texture, and hardness. Grades K, 1, 2, 3, 4, & 5.
- Use physical and chemical properties to identify and describe substances; for example: density, boiling point, and solubility. Grades 6, 7, & 8.
Structure of Systems ( ST01, STI02, STI03, & STI04 )
- Know that matter is made of small particles called atoms and molecules. Grades K, 1, 2, 3, 4, & 5. (ST01 1.2.3)
- Understand that all matter is made up of atoms, which may be combined in various kinds, ways, and numbers to make molecules of different substances. Grades 6, 7, & 8. (ST01 1.2.3)
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.
- A solution is saturated when as much solid material as possible has dissolved in a liquid.
- Different solutions have different saturation points.
- A simple solution is one solid dissolved in one liquid.
3. Lesson set up and Management
Materials:
If you did not make a handout packet, copy Handout # 8.
Set up a water station and a sodium chloride station with 25ml spoons.
Check the student tubs to be sure they have all the materials listed. The mass set can be the small cubes from a Base Ten Kit as they are 1 gram cubes. If your school has the Measurement Kit , there are gram cubes in this kit.
Student Management:
The lesson suggests having the students work in pairs. It is just as easy to keep the same groups of four students, and have them take turns filling and shaking the vial. Also, the post-it notes seem to stick fine without tape. Here is a text copy of the handout with compete instructions.
Reaching saturation
Materials:
In Basin:
Safety goggles
2 bottles with lids
5 plastic cups
1 funnel
2 filter papers
Sticky notes
1 5 ml spoon
Balance
Gram weights
Worksheets and journals
Pencils
At chemistry station:
Kosher salt
25 ml spoon
Water containers
Syringes
Paper Towels
Tape
Procedure:
1. Get the basin of group supplies.
2. Get 50 ml of salt into a plastic cup.
3. Label the cup salt with a sticky note.
4. Put 50 ml of water in both plastic bottles.
5. Put a sticky note so the top of the note is at the top of the water level in the bottles.
6. Using the funnel, without a filter, put salt into one of the bottles, using 5 ml spoonful increments.
7. Cap and shake the bottle between each spoonful.
8. Keep track of the number of spoonfuls added, and make observations after each spoonful, making sure to note the water level each time.
9. Note when you have a saturated solution in your data.
Part 2
1. Place a short cup labeled salt solution under the funnel.
2. Get and dampen a filter (not dripping), and place it in the funnel.
3. Shake then pour the salt solution through the damp filter.
4. Place the salt solution on the balance.
5. Take an empty short cup and place 50 ml of water into it.
6. Place it on the other side of the balance.
7. Place gram cubes one at a time into the short cup with 50 ml water until the balance is level.
8. Note how many gram cubes you used in your data.
The students will use the funnel without a filter to put the salt into the vials. Be sure to demonstrate how to do this for the whole class to save time with individual questions later. Also, make sure the students understand that they must shake the vials thoroughly. A common mistake is that students stop too early and think their solution is saturated. Have students discuss why they think the filter needs to be wet prior to filtering the salt solution, and before setting the solution on the balance.
Put results on the board or on an overhead and keep the results there so the students can compare with their next investigations.
Writing Support:
Have students record the class results on the back of Handout # 8 or in their journal, and write what they know about saturation from this activity. Then have students share, initially in groups, then as a class, what they know, and ask them for definitions of solute, solvent and saturated solution. At the end of the discussion, give students the definitions in the teacher's manual.
Reading Support:
Read the “Decompression Sickness” selection in the Mixtures and Solutions: Science Stories book.
Be sure to explain to students the connection between the condition in the reading selection and the investigation they completed. Before reading, tell the students that there are many chemicals and gasses dissolved in their blood. In this way, blood can be thought of as a solution. Explain that changing atmospheric pressure affects their bodies by changing the amount of solute, chemicals and gasses, that will dissolve in their blood.
An extension of this idea can be found in cake mixes. Bring one in and read the high altitude instructions. Tell the students that atmospheric pressure is different above sea level as well as below sea level.
Virginia Mason Hospital in Seattle, which contains a hyperbaric chamber, may be a good resource for this reading selection.