Lesson

Background

Today you will be given a recipe to make a delicious German chocolate cake. In this activity you will apply three key concepts from classroom learning. Using your calculator, you will perform English to metric conversions. You will visualize in your mind the process of making a cake and identify the chemical and physical changes that occur. Finally, you will distinguish between a compound and a mixture during the process.

Prelab Questions

• Give an example of an element and an example of a compound.
• Explain why a cake is a homogeneous or heterogeneous mixture.
• While making a cake, how can you identify whether each step is a chemical or physical change?

Objectives

• Practice English to metric conversions.
• Identify three states of matter.
• Classify ingredients as compounds or mixtures.
• Distinguish between chemical change and physical change.

Materials

• Student worksheet
• Calculator
• Pencil / Pen
• Metric to English conversion table

Procedure

1. The following recipe was used for this lesson: http://bit.ly/cake-conversion
2. Complete the table below:
   1. Next to each ingredient in the “State” column cell write “S” if it is a solid, “L” if it is a liquid, and “G” if it is a gas.
   2. Next to each ingredient in the “Mixture or Compound” column cell write a “C” if it is a compound or “M” if it is a mixture.
   3. For each ingredient that is identified as a compound write its chemical formula in the “Formula” cell. You may need to look it up.
   4. For each ingredient that is identified as a mixture indicate whether it is heterogeneous or homogeneous in the last column of the table.
3. Complete the metric to English calculations and conclusions sections. The required conversions are included in the conversion table and at the end of these instructions

Calculations

Convert the following ingredient units using your conversion table. Note that the temperature and pan size were not ingredients but must still be converted. For full credit please show your work with proper dimensional analysis and number significant figures.

Analysis

1. Why didn’t you need to convert the baking time from the metric recipe?
2. Find and explain two steps in the recipe that involve physical changes. Explain how you know they are physical changes.
3. Find and explain two steps in the recipe that involve chemical changes. Explain how you know they are chemical changes.
4. Baking involves many chemical changes. One of those changes allows the cake to rise. The main mechanism for this is the release of carbon dioxide. Which compound(s) from the ingredients list do you think releases this carbon dioxide? How do you know?
5. The recipe instructs you to cook for 25-35 minutes. One of the reasons cook time might vary is the size of the pan you select. Which size pan would take less time to cook and why?
6. Another variable that can affect bake time is what the pan is made of. What differences will there be if you bake you cake in a glass pan vs. an aluminum pan? (You can research this topic)
7. When opening the oven to remove your cake, why would it be smart to close your eyes and hold your breath for the first few seconds?
8. The recipe notes that if baking at high altitude add 3 tablespoons extra flour. Why would you add more flour if cooking at higher altitudes?
9. Write a brief summary of what you learned in this lab that includes how the objective was met.