Types of Mixtures Lab

Background Information: Polarity In the middle of the night of March 24, 1989, the giant oil tanker Exxon Valdez veered out of the shipping lanes in Alaska’s Prince William Sound and struck a reef. The side of the tanker was ripped open, and 11 million gallons of crude oil flowed out into Alaska’s clear blue waters. Because petroleum oil is insoluble (does not dissolve) in water and less dense, it quickly spread across the surface. The oil slick eventually covered 10,000 square miles, contaminating 1500 miles of shoreline, and causing substantial damage to wildlife, the fishing industry, and the marine environment.

Chemists say “like dissolves like,” meaning that polar solvents tend to dissolve polar solutes, and nonpolar solvents tend to dissolve nonpolar solutes, while nonpolar and polar substances are immiscible (do not mix). Because petroleum is nonpolar and water is polar, the oil from the leaking Exxon Valdez did not mix with the seawater, but rather spread across its surface.

Pre-lab Questions (1) What is the difference between a heterogeneous mixture and a homogeneous mixture? (2) Compare and contrast the properties of solutions, colloids, and suspensions. (3) What is the difference between the “solute” and the “solvent?” (4) How does a “phase” of matter differ from a “state” of matter? (5) Explain the rule like dissolves like. Use the terms “miscible,” “immiscible,” “polar,” and “nonpolar” in your answer.

Materials 7 cupsGraduated cylinderSpoon BeakerMilkStarch DropperOilSucrose FlashlightSaltTest tubes and holder Food coloringSandWater

Procedure (1) Prepare mixtures in different cups with about 200 mL of water and the following substances: (a) 3 teaspoons of sucrose (b) 1 teaspoon of starch (c) 1.5 teaspoons of sand (d) 5 drops of food coloring (e) 20 mL of oil (f) 0.5 teaspoons of salt. In the final cup (g), mix 50 mL of milk in 150 mL of water. (2) Stir the contents of each mixture and record the appearance of each mixture immediately after stirring. Then observe the mixtures and their characteristics over the next 10 minutes.

Record your observations. (3) Note which mixtures do not separate after standing. Transfer 10 mL of each of these mixtures to an individual test tube. Shine a flashlight through each mixture. Make a note of the mixture(s) in which the path of the light beam is visible (this is called the Tyndall Effect, see the illustration below).

Analysis and Conclusions: Use Complete Sentences! |Type of Mixture |Heterogeneous or Homogeneous? |Separate After Standing? |Tyndall Effect? | |Solution |Homogeneous |No |No | |Suspension |Heterogeneous |Yes |Yes | |Colloid |Heterogeneous |No |Yes |

(1) In each mixture you made, identify the states of matter that were present. (2) Which of the mixtures were heterogeneous? Homogeneous? (3) Which of the mixtures were suspensions? Colloids? Solutions? (4) What substance was the solvent in the solutions you created? (5) In each of the suspensions created, identify which substance was least dense and explain how you know this. (6) Is water polar or nonpolar? Which of the tested substances are polar, and which are nonpolar? How do you know? (7) What type of polarity must “sunblock” lotion have if it is “waterproof” (doesn’t wash off when you go swimming)? Explain your answer.

Analysis and Conclusions: Use Complete Sentences! |Type of Mixture |Heterogeneous or Homogeneous? |Separate After Standing? |Tyndall Effect? | |Solution |Homogeneous |No |No | |Suspension |Heterogeneous |Yes |Yes | |Colloid |Heterogeneous |No |Yes |

(1) In each mixture you made, identify the states of matter that were present. (2) Which of the mixtures were heterogeneous? Homogeneous? (3) Which of the mixtures were suspensions? Colloids? Solutions? (4) What substance was the solvent in the solutions you created? (5) In each of the suspensions created, identify which substance was least dense and explain how you know this. (6) Is water polar or nonpolar? Which of the tested substances are polar, and which are nonpolar? How do you know? (7) What type of polarity must “sunblock” lotion have if it is “waterproof” (doesn’t wash off when you go swimming)? Explain your answer.

Analysis and Conclusions: Use Complete Sentences! |Type of Mixture |Heterogeneous or Homogeneous? |Separate After Standing? |Tyndall Effect? | |Solution |Homogeneous |No |No | |Suspension |Heterogeneous |Yes |Yes | |Colloid |Heterogeneous |No |Yes |

(1) In each mixture you made, identify the states of matter that were present. (2) Which of the mixtures were heterogeneous? Homogeneous? (3) Which of the mixtures were suspensions? Colloids? Solutions? (4) What substance was the solvent in the solutions you created? (5) In each of the suspensions created, identify which substance was least dense and explain how you know this. (6) Is water polar or nonpolar? Which of the tested substances are polar, and which are nonpolar? How do you know? (7) What type of polarity must “sunblock” lotion have if it is “waterproof” (doesn’t wash off when you go swimming)? Explain your answer. -----------------------

Tyndall Effect, light beam visible, light scattered

No Tyndall; light invisible, not scattered