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Hands-On: Solution Dilution

Description

Students make solutions of salt and water and food coloring and water, and then successively dilute the solution in separate wells of the micro-chemistry tray. After the liquid has evaporated the students observe the resulting precipitate.

Materials for the activity:

Leading the Activity

Review that a solution is a mixture of one or more materials dissolved in a liquid. The solution can be weak or strong depending on how much of the material is dissolved in the liquid. If more water is added to the solution, the solution becomes more dilute. If more of the material is added, the solution becomes more concentrated. Make and display the solutions of salt water, and food coloring in water in front of the students to discuss these ideas.

Ask the students what would happen if we continue to add water to a solution--how long will the properties of the material dissolved in the water remain? How much water can be added until we can no longer tell that there is something dissolved in the water? Describe the investigation and help the students complete the activities.

Procedure

  1. Make a solution of salt and water (or sugar and water) by adding salt to the water until the salt no longer easily dissolves (salt falls to the bottom without dissolving, even if stirred). In another beaker, make a water and food coloring solution by adding food coloring to the water until a medium color is reached. The exact dilution of each solution is not important.
  2. Fill a vial with each solution and give one to each group.
  3. In a well tray, add twenty drops of the solution to the first well.
  4. Take ten drops of the solution from the first well and place it into the second well (squirt the rest of the solution back into the first well). Add ten drops of water to make a weaker solution. Rinse the medicine dropper in clean water before continuing!
  5. Take ten drops of the solution in the second well and place it in the third well. Add ten drops of water to make an even weaker solution.
  6. Continue for several wells until there is no evidence of the original dissolved material visible. Use the food coloring solution as a guide--when there is no color left.

 

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