Salt Solution Activity

Teacher Notes

Students will be carrying water around the room. Expect some spills and be prepared for students to clean them up by having paper or cloth towels on hand.
Explain the dissolving process to the students as they are mixing salt with the water. Emphasize that the salt is not disappearing, but dissolving into the water.
Explain the salt crystals students should see in the dried evaporation trays. Emphasize that this is the salt they had dissolved into the water.

Provide the following materials for each pair or small group of students. Suggest having students in partners or groups of three.

Two cups: Clear plastic cups allow students to make better observations about what is occurring in the cup.
Water: Each group will need about ½ cup of water. Suggest having a measuring cup on hand.
Salt: Each group will need about one teaspoon of salt.
Spoon: Regular or disposable teaspoons work well.
Dropper: Standard eye dropper
Evaporation dish: Example of evaporation dish Petri dishes work well for evaporation. Placing a piece of black construction paper under a clear petri dish will help show the salt crystals.
Balance with mass set: Any balance with mass set will work. A digital scale is another option. If you do not have enough balances for each group to have their own, consider setting up stations around the room for groups to access for measurement.

Obtain all materials, keeping salt and water in separate cups.
Use the balance to find mass of water in cup.
Find mass of salt in cup.
Pour salt into water. Stir with spoon. Record your observations.
Find mass of empty cup.
Calculate the mass of just the salt by subtracting the mass of the empty cup from the mass of the cup and salt combined.
Calculate the expected mass of the salt solution by adding the mass of the cup of water and the mass of just the salt.
Find mass of salt solution.
Compare the expected mass of the salt solution and the actual mass of the salt solution.
Place about 10 drops of salt solution in the evaporation dish.
Leave the in a quiet space of the classroom. Check back in a few days after the water has evaporated. Observe what remains in the evaporation dish after the water evaporates.

Check student mass measurements.

Mass of cup with water ____________ Mass of cup with salt ____________

Mass of empty cup ____________

Mass of salt ____________ <---> Mass of salt ____________

Expected and actual mass of salt solution should match or be close.

Expected mass of salt solution ____________

Actual mass of salt solution ____________

Describe your observation when adding salt to water.

Salt will start to disappear. It is dissolving into the water.

Describe your observations when stirring salt and water.

Salt will dissolving faster when stirring. All salt should dissolve.

Describe your observations of the material in the evaporation tray after the water evaporates.

Tiny salt crystals have appeared.

Identify the solute.

Salt

Identify the solvent.

Water

Identify the material in the evaporation tray after water has evaporated.

Salt

Provide the following materials for each pair or small group of students.

Obtain all materials, keeping salt and water in separate cups.
Use the balance to find mass of water in cup.
Find mass of salt in cup.
Pour salt into water. Record your observations.
Stir with spoon. Record your observations.
Find mass of empty cup.
Calculate the mass of just the salt by subtracting the mass of the empty cup from the mass of the cup and salt combined.
Calculate the expected mass of the salt solution by adding the mass of the cup of water and the mass of just the salt.
Find mass of salt solution.
Compare the expected mass of the salt solution and the actual mass of the salt solution.
Place about 10 drops of salt solution in the evaporation dish.
Leave the in a quiet space of the classroom. Check back in a few days after the water has evaporated. Observe what remains in the evaporation dish after the water evaporates.