The Frigid Gourmet

Drolson, Rochelle Clemente High School

Objectives: Students will be able to explain why the freezing temperature of water has to be lowered in order to make ice cream; they will know what chemicals are used to lower the temperature and how each of these chemicals are soluble in water. Apparatus needed (for a class of 30): 15 graduate cylinders filled with 45 ml of milk, 5 ml of sugar for each cylinder, 3 drops of vanilla for each cylinder, 3 drops of any color food coloring for each cylinder, 15 250 ml beakers, 30 wooden sticks, 30 test tubes, 30 large styrofoam cups, 30 thermometers, 30 small plastic containers, 2 large bags of ice, 500 ml rock salt, 500 ml isopropyl alcohol, 500 ml mineral oil Strategy: CHART: CHEMICALS EFFECTS ON TEMPERATURE SOLUBLE OR SCIENCE MELTING POINT (C) INSOLUBLE SURPRISE OF ICE IN WATER YES OR NO RAISE, LOWER, OR STAY THE SAME ---------------------------------------------------------------------- A. NO CHEMICAL (ICE ONLY) B. ROCK SALT C. ALCOHOL D. MINERAL OIL ______________________________________________________________________ DIRECTIONS FOR MAKING SCIENCE SURPRISE: Step 1: Pair off with another class member Step 2: Picking up equipment a. You and your partner are to pick up the necessary equipment b. Partner 1 - one graduate cylinder, one 5 ml container of sugar, 3 drops of vanilla in cylinder, 3 drops of food coloring in cylinder c. Partner 2 - one 250 ml beaker, 2 wooden sticks, 2 test tubes, 2 large styrofoam cups, two thermometers, two small plastic cups Step 3: At your table, mix the ingredients from the graduate cylinder with the sugar in the beaker and stir with the wooden stick. Step 4: Pour l/2 of the mixture from the beaker into each test tube Step 5: Add the wooden stick to the test tube and place the test tube in a styrofoam cup with a thermometer Step 6: Go back to lab station and have your styrofoam cup filled with ice and one of the chemicals according to your group title (A,B,C, or D) MAKE SURE THE MIXTURE IN THE TEST TUBE IS COMPLETELY SURROUNDED BY ICE AND MAKE SURE NONE OF THE ICE AND CHEMICALS GET IN THE TEST TUBE Step 7: Making the science surprise a. Record temperature of the thermometer (as soon as it stops moving) on the chart b. Grasp the top of the test tube with 2 or 3 fingers and twist it back and forth in beaker-do not lift it up c. To see if the mixture is changing, every once in awhile lift up on stick. When the stick starts to stay stuck in the mixture, you know a change is taking place. Step 8: Remove the test tube from the beaker. Rub between your hands for about 20 seconds. Step 9: Grasp the stick and carefully remove the mixture from the test tube Step l0: You have made a science surprise! You may eat it! Step ll: Looking at your chart, fill in the second column for your chemical only. Step l2: Pour a little of the ice water (no ice) from the styrofoam cup into the small plastic container. Is it soluble or insoluble? How can you tell? Step l3: Finish filling in the chart for your chemical only. EVALUATION QUESTIONS: l. What was the science surprise? 2. How had the materials in the test tube changed during the experiment? 3. What had to happen to the materials to make a change? 4. Did all the materials change? If so, why not? 5. Results of the chart a. Fill in as a class the rest of the chart b. Is there a pattern among the materials that changed? What do they have in common? c. Which materials lowered the melting point of ice? d. Which materials raised the melting point of ice? e. With which chemicals did the melting point stay the same? f. With which chemicals did one have a science surprise? g. What do the chemicals that helped to produce a science surprise have in common? h. Name the chemicals (if any) that didn't produce a science surprise. What do they have in common? i. What about those mixtures that used ice only. Did they get a science surprise? Why or why not? j. Do you think to make a science surprise, the temperature of ice has to change? If so, how will it change? 6. Why can't one make a science surprise with ice alone? 7. Form a conclusion about what is needed to make a science surprise. BONUS QUESTIONS l. Why is salt added to the roads in winter to remove ice? 2. Methanol (freezing point is -97.8C; boiling point is 64.7C) was used as an antifreeze in cars. It has been replaced by ethylene glycol (freezing point is -l5.6C; boiling point is l97.6C) WHY?
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