Subject High School Subjects High School Science

Question

Please answer the questions at the end of the lesson.
Lesson:
In the last lesson, we used a living thing, yeast, to create the gas to puff our baking bread. In this lesson, we're going to use the reaction of acids and bases to do the same thing.

You have probably experienced previously what happens when you mix a little baking soda with a little vinegar. If you've never done it before, give it a try. The two chemicals react to produce a gas, in this case carbon dioxide.

For this lesson you will need to have a way to test general pH. You can sometimes find pH paper or garden soil testing kits at garden centers or even drug stores. If you have problems finding it, you can make your own with the instructions here. Even if you do not need to make your own pH indicator, you should read the linked page for general pH information. You only need to do what you need of the activity in order to make the pH indicator.

When vinegar and baking soda react, two reactions happen in quick succession:

First, the vinegar (CH3COOH) and baking soda (NaHCO3) react to form two other chemicals: CH3COONa and H2CO3.

H2CO3 quickly breaks down into carbon dioxide (CO2) and water (H2O). It's the carbon dioxide that is let off in the familiar fizzing reaction of vinegar and baking soda.

One important thing to note about reactions is that they are balanced. For example, let's look at the first reaction above:

CH3COOH + NaHCO3 -----> CH3COONa + H2CO3

On the left side of the arrow we have 3 atoms of C, 5 atoms of H, 5 atoms of O, and 1 atom of Na. For this to be balanced, we need to come up with the same thing on the right. And we do, the atoms are just rearranged into different compounds!

The second reaction above is also balanced:

H2CO3 -----> CO2 + H2O

On the left we have 2 atoms of H, 1 atom of C, and 3 atoms of O. And on the right, we have the same thing! The reaction balances.

Read the entire lesson including the questions before you begin.

You will need:

3 cups whole wheat flour*
1 cup all-purpose flour*
1 tsp baking soda
1/2 tsp salt
1 and 3/4 cups buttermilk (may need a little more, see directions)
4 tbsp butter
1 egg
one small bowl (to melt butter)
one mixing bowl
one mixing spoon
one whisk
one loaf pan
cooking spray (such as Pam) and a little extra flour for dusting

Melt butter in small bowl in microwave. Let cool before allowing to mix with egg (I mix some of the buttermilk in to help cool it down).

Break egg into mixing bowl, discard shell, and beat (stir) egg with whisk. You want it to be an even yellow tone.

Slowly add the buttermilk to the egg, and continue stirring so they are well mixed. Add the butter in the same way.

Add all the dry ingredients to the liquids, stirring to mix thoroughly. The result should be a batter that you can pour from the bowl -- if it turns out to be too thick, add more buttermilk (add slowly, mixing well, since you don't want too much) until the dough is pourable. (See the "Note" below if your dough is too thick and you run out of buttermilk.)

Spray the loaf pan with cooking spray. Make sure your middle oven rack is low enough that the bread pan will sit in the middle of the oven with room above and below, and preheat the oven to 400 degrees F.

Pour the contents of the bowl into the prepared pan to about 3/4 full (a little more won't hurt). Bake the bread in the oven for 50 minutes (if you take it out too soon the center will not be baked). Remove from oven. It is not necessary to remove from the pan immediately.

Assignment:
1. What are the acid and the base in this recipe? Use your pH tester to find out. (Dry ingredients can be mixed with a little water for testing [test the water pH so you don't get fooled into thinking something is alkaline or acidic when it's not], or dry ingredients can be added to a little bit of liquid pH testing solution.)

2. In the lesson we saw that

H2CO3 -----> CO2 + H2O

But what if there were two molecules of H2CO3? How many molecules of carbon dioxide and water would it produce? (Remember two molecules of H2CO3 would mean you need to double each part!)

3. Write out the symbol equation for the reaction from question 2. Two molecules of H2CO3 (written as 2H2CO3) would be how many molecules of carbon dioxide and water? (The subscripts won't show up in your answer, but that's okay, just put in the numbers and your instructor will know you mean them to be subscripts.)

2H2CO3 -----> ?

4. You've now made bread using yeast in one lesson, and using baking soda in another. Name two benefits of using yeast.

5. You've now made bread using yeast in one lesson, and using baking soda in another. Name two benefits of using baking soda.

Solution Preview

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1.
Baking soda is a base.
Buttermilk is acidic due to the lactic acid in milk....

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