This term, our Biol 342 lab is working at home. This course is designed for Combined Majors in Science students and this is their lab on cake. In this lab, they compare volume of a standard cake recipe with chemical leavening to volume of a cake where they have stoichiometrically balanced the acid and base involved in the leavening to a third cake were they have substituted the type of acid.

Preparation and Supplies

1 oven or toaster oven
1 9” cake pan OR 1 8” square pan
all purpose flour (1 1/2 c)
sugar (1 c)
baking cocoa (1/4 c) (NOTE: this is different than hot chocolate. Cocoa is unsweetened)
salt (1/2 t) (NOTE: “t” = teaspoon)
baking soda (1t)
vanilla extract (1t)
cider or white vinegar (1T) (NOTE: ’T’ = tablespoon)
another food safe acid (such as orange juice or lemon juice)
vegetable oil (1/3 c)
cold water (1 c)
a ruler or measuring tape


Students work in groups of 3 (remotely). One person bakes an old King Arthur Flour cake recipe. A second will bake the same cake, but with a molar balanced amount of vinegar rather than the amount prescribed in the recipe. The third person will bake the same cake, but will swap out the vinegar with another acid.

The basic cake: This recipe is very old. It was developed during world war II when rationing was common and eggs (a leavening agent) were scarce. This cake is so popular, it was selected as the Recipe of the Centuries by King Arthur Flour. The original recipe can be found here, which includes a simple icing if you’d like to include that on your cake: https://www.kingarthurflour.com/recipes/king-arthurs-original-cake-pan-cake-recipe

Instead of eggs, this cake recipe uses baking soda and vinegar to leaven the cake. Leavening is the addition of air pockets into your baked product. If you think of breaking open a loaf of bread, there are often large air pockets inside. These pockets form from CO2 released during leavening. The gas is trapped in the matrix of the flour, forming pockets. This process can be accomplished biologically through yeast, which metabolize sugar and release CO2, egg whites, which hold air pockets when whipped, or other agents. Leavening can also be accomplished chemically with the addition of an acid and a base.

We assume that our different recipes will result in cake with the same volumes. In your lab notebook, write a testable scientific hypothesis.

The basic recipe (person 1 bakes this)

Ingredients
1 1/2 cups (177g) All-Purpose Flour
1 cup (198g) sugar
1/4 cup (21g) cocoa powder
1/2 teaspoon salt
1 teaspoon baking soda
1 teaspoon vanilla extract
1 tablespoon (14g) vinegar, cider or white
1/3 cup (67g) vegetable oil
1 cup (227g) cold water

Instructions
(1) Preheat your oven to 350°F (see lab 1 for adjustments your oven may need). Lightly grease an 8″ square or 9″ round pan that’s at least 2″ deep. You can use a very small amount of oil or butter to grease the pan.
(2) Whisk the dry ingredients together in a medium-sized bowl. Whisk the vanilla, vinegar, vegetable oil, and water in a separate bowl. Pour the wet ingredients into the bowl of dry ingredients, stirring until thoroughly combined. Pour the batter into the prepared pan.
(3) Bake the cake for 25-30 minutes, until a toothpick or knife inserted into the centre comes out clean, or with a few moist crumbs clinging to it. Carefully remove from the oven using oven mitts and let cool.
(4) Using a tape measure and your geometry skills, calculate the volume of your cake. The entire class should discuss how to do this to make sure all our data is obtained the same way.
(5) Upload a photo of your cake with the volume and your assigned type of cake (1, 2 or 3)

Work with your lab group to answer the following questions. Make sure these are in your lab notebook.

1. Evaluate the basic recipe above. Ignoring the cocoa, what is the acid present in this recipe? What is the base?

The recipe calls for 1 teaspoon of baking soda. The chemical formula is NaHCO3.

2. What is the molecular weight of baking soda?

3. One teaspoon of baking soda weighs approximately 4.8 g. How many moles are in 1 teaspoon of baking soda?

Vinegar is acetic acid. The chemical formula is CH3COOH.

4. What is the molecular weight of acetic acid?

When baking soda and acetic acid combine, the following reaction occurs:

NaHCO3 + HC2H3O2 → NaC2H3O2 + H2O + CO2

5. What is the gas given off during this reaction? (This will leaven your cake)

6. Balance the equation above. (Reminder: Count number of each element on each side and make sure nothing is gained or lost during this process…)

7. How many moles of acetic acid will you need to completely react with all the baking soda called for in the recipe?

8. What is the weight of acetic acid required?

9. One teaspoon of vinegar weighs approximately 4.8 g. What volume of vinegar will you add to your perfectly balanced cake?

A perfectly balanced cake (Person 2 bakes this)
Ingredients
1 1/2 cups (177g) All-Purpose Flour
1 cup (198g) sugar
1/4 cup (21g) cocoa powder
1/2 teaspoon salt
1 teaspoon baking soda
1 teaspoon vanilla extract
the amount of vinegar calculated above
1/3 cup (67g) vegetable oil
1 cup (227g) cold water

Instructions
(1) Preheat your oven to 350°F (see lab 1 for adjustments your oven may need). Lightly grease an 8″ square or 9″ round pan that’s at least 2″ deep. You can use a very small amount of oil or butter to grease the pan.
(2) Whisk the dry ingredients together in a medium-sized bowl. Whisk the vanilla, vinegar, vegetable oil, and water in a separate bowl. Pour the wet ingredients into the bowl of dry ingredients, stirring until thoroughly combined. Pour the batter into the prepared pan.
(3) Bake the cake for 25-30 minutes, until a toothpick or knife inserted into the centre comes out clean, or with a few moist crumbs clinging to it. Carefully remove from the oven using oven mitts and let cool.
(4) Using a tape measure and your geometry skills, calculate the volume of your cake. The entire class should discuss how to do this to make sure all our data is obtained the same way.
(5) Upload a photo of your cake with the volume and your assigned type of cake (1, 2 or 3)

For the third recipe, you will substitute the acid in the cake.
Choose an edible acid from your kitchen. Orange or lemon juice is a good choice. Work with your group to answer the following in your lab notebook:

1. What is the acid ingredient you chose?
2. What is the balanced reaction of your acid with baking soda? (NOTE: you can look this up)
3. What percentage of your ingredient is actually acid? (i.e. orange juice is about 1.5% acid)
4. How much of your ingredient do you need to add to include enough acid to react with all the baking soda?

The remainder of the volume of your ingredient is mostly water, so adjust the water in the recipe as necessary. (If you use orange juice, you may not need to add any water…)

A new acid cake (Person 3 bakes this)
Ingredients
1 1/2 cups (177g) All-Purpose Flour
1 cup (198g) sugar
1/4 cup (21g) cocoa powder
1/2 teaspoon salt
1 teaspoon baking soda
1 teaspoon vanilla extract
the amount of your acid ingredient calculated above
1/3 cup (67g) vegetable oil
1 cup (227g) cold water – adjusted for water in your acid

Instructions
(1) Preheat your oven to 350°F (see lab 1 for adjustments your oven may need). Lightly grease an 8″ square or 9″ round pan that’s at least 2″ deep. You can use a very small amount of oil or butter to grease the pan.
(2) Whisk the dry ingredients together in a medium-sized bowl. Whisk the vanilla, acid, vegetable oil, and water in a separate bowl. Pour the wet ingredients into the bowl of dry ingredients, stirring until thoroughly combined. Pour the batter into the prepared pan.
(3) Bake the cake for 25-30 minutes, until a toothpick or knife inserted into the centre comes out clean, or with a few moist crumbs clinging to it. Carefully remove from the oven using oven mitts and let cool.
(4) Using a tape measure and your geometry skills, calculate the volume of your cake. The entire class should discuss how to do this to make sure all our data is obtained the same way.
(5) Upload a photo of your cake with the volume and your assigned type of cake (1, 2 or 3)

Before enjoying your cake, let’s think back to that hypothesis you generated. How will you test this hypothesis?

To start, you will make some simple measurements and calculate the volume of your baked cake. (Your cake is likely domed in the centre, so one good way might be to measure the height of your cake at the edge, and use this to calculate the volume of your cake base. Then measure the height of your cake at the centre and calculate the volume of the domed “lid”. You will be making assumptions on the shape of this dome, but this should be a close estimate.)

Enter your volume calculations into your lab notebook. Also enter the volume of your cake into with the type of cake you baked (1,2, or 3).

By the end of the week, we will have collectively baked a lot of cakes. How will we evaluate cake volume quantitatively to test our hypothesis?
Because we have 3 populations (basic, balanced, and new acid), we will use an ANOVA test. (Note for future: If we had 2 populations, we could use a t-test).