Lesson 1 Science

The Appearing Salt



http://edweb.sdsu.edu/triton/JGarciaResearch/LessonTemplate1.html

by

Jackie Bonventre
Russ Nielsen

Objective

The students will understand what saltwater is and what it can be used for.

Direct Instruction


You can start class by asking one of the students to drink a glass of saltwater. (Most students will turn their nose up!) Next, share the statistics on the enormous amount of saltwater and limited amount of freshwater which exists on the earth. With this information, the students will wonder how we can make use of the giant resource of saltwater.

One way to brainstorm ideas of things we can do with saltwater is to create our own saltwater in the lab and experiment. Model the beginning of the experiment of making saltwater out of regular table salt and purified water. Explain each of the steps in "The Appearing Salt" experiment. With the remaining saltwater, water a plant in front of the entire class. The plant can be observed at the beginning of each class for the remaining time of the unit plan. Eventually the plant will dry out and die because the saltwater actually pulls the moisture froms the plant.

Lab

The experiments will allow the student to purify their own water. They first have to make their own saltwater by mixing 1g of table salt with 10ml of purified water. Mix the solution until all the salt dissolves. Next, the students will warm up the solution so the water evaporates. The remaining film can then be weighed to see if it matches the original 1g of table salt.

While the students are waiting for the water to evaporate, allow them to make a larger quanitity of saltwater. This will be used for freezing in ice trays to be veiwed the following day.
Materials

  1. Beaker of purified water, 10ml.
  2. 1 gram of table salt
  3. shallow pan
  4. heating source

Directions
  1. Measure out and add 1 gram of table salt to 10ml of water.
  2. Mix until salt is completely dissolved, note that the water is clear.
  3. Pour the water into a shallow pan and gently heat until all the liquid is dissolved.
  4. Inspect the pan. What did you find?


Discussion

Observe the water is clear before evaporating. Notice a white residue starts to form as the liquid evaporates. Identify residue as table salt. From this you can generalize that evaporation can be used to purify saltwater.

Homework

The students must write a summary of what happened during their lab. They must include an explanation of why this occurred.

Last updated May 18,1997.

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