Hands-on science (no lab required).
Which type of chocolate has a lower melting point: a candy-coated or non-coated chocolate? Does the size of a piece of chocolate affect its melting time?
5 plastic bags (sealable, quart-size) ** chocolate (1 M&M, 2 whole Hershey's Kisses, 2 Hershey's Kisses cut in half) ** thermometer * 5 plastic cups (8 oz, or 250 ml) ** *2 milk jugs (4 L, or 1 gal)-one filled with 27[degrees]C (80[degrees]F) tap water, and the other with 40[degrees]C (105[degrees]F) tap water ** watch or timer ** tablespoon ** paper (graph and plain) ** pencil
* See teacher's note, TE 7
* Teacher's Note: The two jugs of water should be sufficient for a whole average-size class.
1. The M&M should have resulted in the highest melting point. That's because the water's heat has to travel through the M&M's coating before it reaches the chocolate inside.
2. Yes, the whole chocolate kiss takes longer to melt than the half-size piece. That's because the chocolates melt when enough heat moves from the water to the chocolate. It takes longer to transfer enough heat to raise the temperature of a larger solid compared with a smaller one.
3. The chocolate kisses should melt in your hand, because chocolate's melting point is lower than the average human body temperature: 37[degrees]C (98.6[degrees]F),
1. Divide into groups of 3 to 4 students.
2. Put 1 M&M, 1 Hershey's Kiss, and 1 half-piece Hershey's Kiss into separate plastic bags, and seal.
3. Pour a half-cup (125 ml) of 27[degrees]C (80[degrees]F) water into each of three cups.
4. Measure the cups' water temperatures using a thermometer. Record these temperatures.
5. Place each bag into a cup. Make sure the water level covers the chocolate candies.
6. Time one minute on a watch, and then remove the bags from each cup.
7. Observe each bag for a chocolate smear. This signals melting. (Gently press on the M&M to check for melting.)
8. Record observations.
9. If you don't see a smear, add 2 tablespoons of hot water (40[degrees]C, or 105[degrees]F) to that candy's cup.
10. Repeat Steps 4 to 9 until each piece of chocolate shows signs of melting. The temperature at which each candy melts is its melting point.
11. Place 1 whole and 1 half-piece chocolate Kiss into separate bags, and seal.
12. Get two fresh cups. Combining water from the hot and cool water jugs, fill each cup with a half-cup (125 ml) of water until its temperature reaches the melting point found for the whole chocolate Kiss.
13. Repeat Steps 4 and 5.
14. Time how long it takes for the whole and half chocolate Kisses to melt completely. Record the times.
15. Make two bar graphs: one showing the melting points for all three chocolates, another showing the melting times for the whole and half chocolate Kisses.
1. Using your graphs, which chocolate piece had the highest melting point? Explain.
2. Did the chocolate's size affect its melting time? Why or why not?
3. Which chocolate piece will melt in your hands? Hint: Think about the average human body temperature.
Learn more about candy science at: www.exploratorium. edu/cooking/ candy/index.html.
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|Date:||Nov 1, 2004|
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