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Separate That Solution!

Author: Muriel Gerhard

Grade Level: 7th - 8th; Type: Chemistry

Objective:

Determine how we can separate the components of a solution.

Research Questions:

  • Define each of the following terms: solid, liquid and gas and cite examples of each.
  • What is an element? Provide three examples of common elements.
  • How is an element different from a compound?
  • List three compounds that we use on a daily basis.
  • How is a mixture different from a compound? Provide three examples of common mixtures.
  • In the case of adding sugar to water, which one is the solute and which one is the solvent?
  • How does a super saturated solution differ from a saturated solution?

On the information level, this experiment serves to acquaint students with basic information on how one can separate a dissolved solid such as salt from the solvent, in this case water. In this case, students become acquainted with the method of evaporation and how this method enables us to study a solid. As a result of this experiment students readily understand why a solution is classified as a mixture rather than as a compound. In addition, students begin to develop lab skills and safety skills which will enable them to succeed in future lab courses.

Materials:

  • 4 beakers
  • 4 glass slides
  • 4 medicine droppers
  • 4 stirring rods
  • one 100mL graduated cylinder
  • a grease pencil
  • a magnifying glass
  • tap water
  • distilled water
  • 15mL of Kosher salt

These materials may be purchased from Science Kit or Chem Scientific or borrowed from the school science labs.

Experimental Procedure:

  1. Gather all the materials you will need for this project.
  2. Copy the Data Chart provided below so that you can readily record your observations.
  3. Put on your safety glasses, apron and gloves.
  4. Using your grease pencil, number the 4 beakers. Now, add the amount of water listed below to each of the beakers as follows: beaker #1: 75 mL of tap water, beaker#2: 75 mL of distilled water, beaker #3: 100mL of distilled water, beaker #4: 50mL of distilled water.
  5. Note: When mixing salt or any substance always use a clean stirring rod. Now, add 15mL of table salt to beaker #3and stir until the salt is completely dissolved. That means you do not see any solid particles of salt in the water.
  6. Measure 25mLof salt water solution from beaker3 and add it to beaker #4. Mix using a clean stirring rod.
  7. Take your slides and label them numbers 1, 2, 3, and 4 using the grease pencil. Now, using a clean medicine dropper, put 5 drops of water from beaker 1 onto slide 1.
  8. Use separate, clean medicine droppers to put 5 drops of solution from each of the other three beakers onto the slide with the same number as the beaker.
  9. Put the 4 slides in a warm place overnight.
  10. Now, examine the residue on each of the four slides using a magnifying glass. Record your observations on the data chart.
  11. Respond to the following questions on your data chart: ( a) Which of the beakers had the saltiest solution?  (b) What effect did the 5 drops of solution have on the slides left overnight? (c)Describe the residue left on the each of the slides? (d)How do you account for the differences in slides #1,#3 and #4?(e)  What does the amount of residue on slides #1 and #2 tell you about the use of tap water and the use of distilled water? (f)Why do you think we used kosher salt as opposed to regular salt?
  12. The method you used is labeled The Evaporation Method. (g)What does this method enable us to do? 

Data Chart #1

 

               Slides

Description  of Residue

            #1

 

            #2

 

            #3

 

            #4

 

 

Data Chart #2

 

                                  Questions

                               Responses

Which beaker had the saltiest solution?

 

What effect did the 5 drops have overnight?

 

How account for differences in slides #3and #4/

 

What does the amount of residue on slides 1and 2 tell you?

 

Kosher salt versus regular salt! Why?

 

 

Terms/Concepts: solids; liquids; gases; element; compound; mixture; solution; solute; solvent; saturated; super saturated

References:

  • Chem Com, American Chemical Society, Kendall Hunt Publishing Co, 1988
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