Chemistry: Matter and Change

Chapter 3: Matter - Properties and Changes

Problem of the Week

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Chemistry in Action
Cooking is the oldest and most widespread application of chemistry. Every cook is a chemist. The first chemical laboratories were kitchens in the Middle Ages. Recipes are the oldest practical result of chemical research. Many chemical processes have been derived from cooking techniques. These techniques include making sauces and meringues, baking, marinating and tenderizing meat, and caramelizing sugar.
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Cooking is chemistry in action, with the added benefit that you can eat the results. As you follow the recipe below for peanut brittle, make observations about the changes that occur.
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Recipe for Peanut Brittle
  • 2 cups granulated sugar (sucrose)
  • 1 cup corn syrup (glucose)
  • 1 teaspoon water
  • 3 cups peanuts, raw or roasted
  • 3 tablespoons margarine
  • 1 teaspoon vanilla
  • 1 teaspoon baking soda
  • wooden spoon
  • hot mitts
  • candy thermometer
  • heavy, 2-quart saucepan

CAUTION: Mixtures will be very hot.

1. To check the accuracy of your thermometer, bring a small pan of water to the boiling point. Take the temperature of the boiling water. If the thermometer reads above or below 212°F, add or subtract the same number of degrees from the temperatures in the following steps of this recipe.

2. Use 1 tablespoon of margarine to lightly grease the surface of two baking sheets. Keep the baking sheets slightly warm.

3. Combine the water, corn syrup, and sugar in the saucepan. Stir until the sugar is dissolved. Place the thermometer in position in the pan. Be sure the thermometer does not touch the bottom of the pan.

4. Heat the sugar solution rapidly to 280° F to ensure the desired concentration of sugar in solution. As the mixture heats, the water evaporates and the concentration of the sugar solution increases and a syrup forms. Only stir enough to keep the mixture from scorching.

5. When the syrup reaches 280° F, add the peanuts and margarine. Stir the mixture continuously and heat to 300° F. The syrup will turn from clear to yellowish brown due to a process known as caramelization.

6. At 300° F, called the hard crack stage, remove pan from heat immediately.

7. Immediately add the vanilla and baking soda and stir. The mixture will foam slightly due to the release of carbon dioxide.

8. Pour approximately half of the mixture on each baking sheet and spread into as thin of a layer as possible.

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