Key ConceptsFor a liquid to dissolve a solid, the molecules of the liquid and solid must attract one another.The bond between the oxygen and hydrogen atoms (O–H bond) in sugar (sucrose) gives the oxygen a slight negative charge and the hydrogen a slight positive charge. Sucrose is a polar molecule.The polar water molecules attract the negative and positive areas on the polar sucrose molecules which makes sucrose dissolve in water. A nonpolar substance like mineral oil does not dissolve a polar substance like sucrose.
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Students will observe the dissolving of the sugar coating from an M&M when it is placed in water. Students will then help design an experiment to see if the type of liquid the M&M is placed in affects how much of the coating dissolves.
Students will be able to explain, on the molecular level, how the polar characteristic of water and sugar interact so that water dissolves sugar. Students will be able to identify and control the variables in their experiment. Students will also be able to explain why a nonpolar liquid, such as mineral oil, is not good at dissolving sugar.
Download the student activity sheet, and distribute one per student when specified in the activity. The activity sheet will serve as the “Evaluate” component of each 5-E lesson plan.
Be sure you and the students wear properly fitting goggles. Isopropyl alcohol is flammable. Keep it away from flames or spark sources. Read and follow all warnings on the label. Dispose of isopropyl alcohol and mineral oil according to local regulations. Warn studens not to eat the M&M’s.
Materials for Each GroupM&M’sWaterMineral oilIsopropyl alcohol (70%)Small white plastic plate3 clear plastic cupsWhite paper
Have students place an M&M in a cup of water and observe.
Question to Investigate
What happens to the sugar and color coating of an M&M when it is placed in water?
MaterialsClear plastic cupWaterM&MWhite paper
Pour enough room-temperature water into clear plastic cup so that the water is deep enough to completely cover an M&M and place this cup on a piece of white paper.
The coating will dissolve from the M&M, revealing a white layer under the color and then the brown chocolate underneath. The colored coating of the M&Ms will collect in a circular pattern around the M&M. Students may also mention the white streaks in the water from the sugar coating.
Discuss student observations.
Ask students:What do you notice about the M&M and the water? The color comes off and moves through the water in a circular pattern. What do you think is happening when the color and sugar come off the M&M? Point out to students that because the water makes the colored coating come off the M&M and mix into the water, the water is dissolving the sugar and color.
Note: There are actually two processes happening in this activity. The color and sugar are dissolving in the water but they are also diffusing. In order to focus on the amount that dissolves from an M&M, students should look at the amount of coating missing from the M&M, instead of the size of the circle of color in the water.Knowing what you do about the polarity of water, why do you think water dissolves sugar?Students may think that sugar is made of ionic bonds like salt. Or they might think that sugar has positive and negative areas and this is why water is attracted to it.Explore
Have students conduct an experiment to compare how well water, alcohol, and oil dissolve the sugar and color coating of an M&M.
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Ask students to make a prediction:Do you think water, alcohol, or oil would be better at dissolving the sugar and color coating of an M&M?
Discuss with students how to design an experiment to compare how well water, alcohol, and vegetable oil dissolve the color and sugar coating from an M&M. Be sure students identify variables such as:Amount of water, alcohol, and oil usedTemperature of each liquidSame color of M&MTime and location the M&M’s are placed in each liquid
Question to Investigate
Is water, alcohol, or oil better at dissolving the color and sugar coating from an M&M?
Materials3 M&Ms (same color)WaterMineral oilIsopropyl alcohol (70%)3 clear plastic cupsWhite paper
ProcedureLabel 3 cups Water, Alcohol, and Oil. Add 15 mL of water, alcohol, and mineral oil to their labeled cups.Place the three cups on a white sheet of paper.
At the same time, add 1 M&M to each liquid. Then gently swirl the liquid and M&M in each cup for about 30 seconds.