Name: ______Block:______Date:______

Lab: “Likes Dissolve Likes”

Purpose: To examine the relationship between a compound’s polarity and its solubility in water.

Background: Have you heard that “Oil and water don’t mix”? Why is this statement true? Even though oil will not mix with water, water is considered to be the universal solvent. The reason being it is readily available and its polar nature. Polar molecules not only dissolve polar molecules but also ionic compounds. Remember, in a polar bond the two atoms are not sharing the electrons equally causing positive and negative poles. Those charged poles then become attracted to the opposite charged pole of another and able to dissolve. This process is called salvation. In this experiment, you will explore the idea of likes dissolve likes and use this idea to identify polarity of substances.

Materials:

*spatula * eye dropper/pipet *basket of substances *test tube rack with test tubes

Procedure:

  1. Record the chemical formula, physical state, and color of each substance in the observation table.
  2. Place clean test tubes in the test tube rack
  3. Fill each test tube with 5 mL of water
  4. Test each of the substances for water solubility by adding a small amount of each substance to an individual test tube.
  5. If you do not have enough test tubes for all substances you will have to empty out the test tubes, wash them, then reuse.
  6. Be careful not to contaminate the chemicals with one another
  7. Flick the test tube gently and note what happens.
  8. If all substance dissolves, add another small quantity and flick gently
  9. Repeat the process several more times if the material continues to dissolve
  10. Describe each substance as insoluble(INS), slightly soluble(SS), or very soluble(VS), based on the observed behavior from 5 a & b in the data table.

Data Table:
Name / Formula / Color / PhysicalState / Solubility in water
Sodium Chloride
Sodium Thiosulfate
Sulfur / S8
Copper ( II) Sulfate
Starch / C6H10O5
Sodium bicarboante
Sucrose / C12H22O11
Acetic Acid
Glycerin / C3H8O3
Oil / C6H5O6
Isopropanol / C3H7OH

Analyses and Conclusions:

  1. Which substances did not dissolve in water?
  1. What basis can you use to decide whether the substances tested are polar or nonpolar?
  1. What is a polar molecule?
  1. Which substances were polar molecules? How do you know this?
  1. Which substances were ionic? How do you know this?
  1. What is a nonpolar molecule?
  1. Which substances are nonpolar molecules? How do you know this?
  1. Polar and Ionic substances generally dissolve in water; nonpolar substances do not. Explain.
  1. Explain why water is such an excellent solvent.
  1. Explain why oil and water do not mix.

Going Further: (Extra Credit)

Based on the results of this lab, explain how soaps and detergents are able to emulsify oils and greases in a solution of water. (you might have to do some research)