Take a moment to observe the two layers of oil and vinegar as they avoid mixing with one another. Using a clean pipet, add 8 mL of oil to each test tube.Using a pipet, add 8 mL of vinegar to each test tube and swirl to fully mix in the emulsifier.Label each test tube with the emulsifier that was added, and label the empty one “control.” Label the data sheet with the emulsifiers you will test. To each of three test tubes, add 2 g of an emulsifier to be tested, putting a different emulsifier in each test tube.Use a scale to measure 2 g of each of the emulsifiers you will test.Set out four clean 20-mL test tubes in a test tube rack.Because oils also repel water, they are called hydrophobic, which means “water-fearing.” Oils repel polar molecules such as those found in vinegar. You can observe this phenomenon by placing a few drops of oil on the surface of a bowl of water-eventually the drops will form a single large oil slick. Most of the atoms in a fatty acid molecule share electrons evenly and are neither negatively nor positively charged (although fatty acids do contain small regions of polarity-just not enough to make the whole molecule polar.) Nonpolar molecules love other nonpolar molecules and will glom together when mixed with water. Fats and oils are composed primarily of long molecules called fatty acids (usually bound together by glycerol molecules into groups of three called triglycerides). Oils are a type of fat (like butter, shortening, and lard) and are considered nonpolar. Polar molecules are attracted to water molecules-which are also polar-and are called hydrophilic, which means “water loving.” Polar molecules are generally attracted to other polar molecules because their slightly negative poles have an affinity for their slightly positive poles. These slightly charged poles arise because one or more atoms in the molecule are electronegative, meaning that they tug electrons-which are negatively charged-towards them, creating an uneven distribution of charge within the molecule. Water, acetic acid, and alcohol are all examples of polar molecules-molecules that have a slightly negative charge at one end, or pole, and a slightly positive charge at another end. Most vinegars are solutions of acetic acid and water (plus some other acids and alcohols, depending on the type of vinegar you are using). Find this lesson on the Science Friday site for supporting multimedia to use as extensions to this lesson.They could also experiment with other vinegars or oils to see how separation times differ, or investigate the effect of temperature on separation time. Students can repeat the procedure with other herbs or spices, such as salt and pepper, to see how they effect the separation time.You may wish to modify this procedure with volumes that are appropriate for the lab equipment you use. For classes, it may be helpful to premeasure individual allotments for each student/group.When students complete the lab, instruct them how to clean up their materials and dispose of any chemicals.Students should wash their hands thoroughly before leaving the lab.Unfortunately, if you work in a space or with equipment where nonfood safe materials are handled (such as a laboratory), you should not taste your results.Clear plastic vials or cups will work for this activity, but they will be much harder to clean and reuse. Avoid swallowing, shaking, inhaling, or sniffing these products during the activity. The dry mustard and vinegar used in this activity can cause respiratory irritation if inhaled.While the materials used in this activity are used in home kitchens every day, please be aware of the following: At least three of the following emulsifiers:.This lesson supports students’ understanding of Recognize that polar and nonpolar substances don’t mix.They use ingredients in salad dressing to relate science to real life scenarios.īy the end of this lesson, students should be able to In this lab, students mix polar and nonpolar substances and then add various emulsifiers to encourage the mixing of the two substances.
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