Project: Coffee cake, acid/base tester, CO2 reactions

Goals: We’re going to make a yummy sour cream coffee cake that can show us how acids and bases react with each other. In this case they are going to react to produce CO2 gas. While the coffee cake is in the oven we’re going to build an acid/base tester with red cabbage. Using our tester we can find different things in the house that are acids and bases. Using those we’ll then do one last quick experiment to show us what is happening while we keep the oven door closed! Remember always ask adults for permission and help when using ovens, stoves or knives in the kitchen!

First we need to gather everything we need for our project. Find everything you need, make sure you have enough ingredients for the project. This way you will not be searching for anything once the fun has begun.

Here are the ingredients you need:

Coffee Cake:
Butter 4 oz
Sugar 8 oz
Eggs 2
Sour cream 8 oz
Flour 1 ½ cps.
Salt ¼ tsp.
Baking Powder 1 tsp.
Baking Soda 1 tsp.
Vanilla 1 tsp
Topping:
Flour 1 ½ Tbsp.
Cinnamon 1 Tbsp
Brown Sugar 1 cp
Butter 1 oz

Acid/base tester:
Red cabbage ½ Head
Water Enough to cover

Oven reaction:
Flour ½ cp.
Baking soda 1 Tbsp.
Vinegar 2 Tbsp
Water ¾ cp.


Here are the materials you are going to need:

Mixing bowls
Spoons and spatulas and a fork
Measuring cups
Measuring spoons
Baking pan (I use a 9” X 9” glass pan, however you can use a tube, bundt,
rectangle or round shaped pan, glass or metal, the time for baking will
vary based on size, shape and type)
Strainer, sieve or colander
Plastic wrap
Cheese grater
Knife (always ask for adult help when using sharp instruments)
Small clear jars or dishes (I use the test tubes, but anything clear will work fine)
Large wide mouth clear container with tight fitting lid (I use a large nalgene water
bottle so we can measure the contents, so straight sides work best. A large
mason jar would be great too!)


Setting up:

Let’s set everything up first. We need the butter, sour cream and eggs to be at room temperature and soft so lets pull those out, measure them and let them warm up. Now pull out the remaining ingredients and tools that we need to have.
Now lets make the Acid/Base tester. First we need to shred the red cabbage. The cheese grater works great, or you can use a knife (remember to ask for help!). If there is a mandoline available, that works best. What you want is to have coarsely shredded or cut red cabbage. Boil enough water (always ask for help when using the stove) to cover the shredded red cabbage in a mixing bowl, cover with plastic wrap or a lid and let sit for at least 30 minutes. When the water has turned a darker red/purple you can strain the liquid in to a container to cool for later!















Mixing:

The butter should be soft now so let’s start making the coffee cake! First, with adults help, start the oven warming at 350°F, grease and flour your baking pan. In a large mixing bowl blend the butter and sugar until its really smooth (like making cookies). Add your 2 eggs, mix until smooth, then repeat with the sour cream and vanilla. In another bowl mix together the flour, salt, baking powder and baking soda. Add the flour mixture to the liquid mixture and blend until well combined. Don’t mix to long, little chunks of flour are ok, but make sure you scrap the bottom of the bowl.

In another bowl mix together all of the ingredients for the topping. A fork works great for this. You want it pretty chunky but well combined.
Pour the cake mixture in to the baking pan and smooth the top, then crumbly the topping evenly over the top. Big chunks are ok! If you feel more challenged at the end, now is the time to mark the volume of the batter on the pan, masking tape and a pen mark will be fine in the oven.













Baking:

Now were going to bake our coffee cake. Have an adult help you put your pan in the oven. I baked mine in a glass pan for about 40 minutes, if your pan is larger it will only take 30 to 35 minutes. If you use a metal pan it will take about 30 to 35 minutes. In a tube or bundt© pan expect 40 to 45 minutes. I recommend a bundt, it will work best with this cake, I used a glass square pan for visibility and what I think most people will have available. Set a timer so you don’t forget!


When the coffee cake is completely baked it will not jiggle as you pull it out and might begin to crack some. The topping will be browned. If you stick a toothpick or skewer into the center it should come out clean, I don’t recommend this though because if it is not finished it might collapse there. Always Get help from adults when working with the oven.









Acid/Base tester:

While the coffee cake is baking lets try to find some different acids and bases in the house. Acids and bases come in different forms. They become more or less acidic or basic because of the presence of ions. Some acids are powders like cream of tarter, sodium aluminum sulfate and sodium aluminum phosphate, these are all commonly found in baking powder and react with water at different temperatures. They then react with baking soda, a base (also a part of baking powder) to produce CO2 gas. In chemistry it would be written like this:

NaHCO3 + H+ → Na+ + CO2 + H2O

Notice a sodium ion (Na+ ) is produced, this increases the saltiness of our coffee cake. Water (H2O) is also produced in the form of steam, also helping to make our coffee cake rise (rising is also called leavening).

Let’s start by testing some different things in the house to see if they are acids or bases. First let’s pour or ladle some of the juice from the cabbage into the clear bowls or jars. Keep one to act as a control to compare too. I used baking soda, baking powder, vinegar, bleach and lemon juice. It takes very little to see a reaction. For the 2 Tbsps of liquid I used about 1/8 a tsp of any one thing I was testing. You will see that things that are basic turn blue and things that are acidic turn pink.

Watch the bleach closely. What color does it turn first and then what color is it after the bleach is fully mixed in? What happens with the baking powder? What would happen if you put some baking powder in to some water, heated it in the microwave and then tested it in the red cabbage juice? (keep your first trial with baking powder to compare). Are there other things in the house that are acids or bases?


Now that we’ve found some acids and bases in the house, let’s find out happening in the oven. In the large clear jar or bottle mix the flour with baking soda. In another cup mix the water and vinegar together. Pour the liquid over the flour, close the lid quickly and tightly and then shake it up until the flour is all wet, then let it sit and watch. The acidic vinegar is reaction with the baking soda to produce CO2. The flour holds the bubbles in making the whole liquid rise, just like in the oven. How much gas was produced by the reaction? Be careful when you open the container to clean it, the contents are under pressure!









How’s the coffee cake coming? Have we pulled it out of the oven yet with adults help? Let it cool before slicing it, but not too much, I like mine still slightly warm! Before we take a bite though, let’s look at one last thing. Look closely at the slice. Do you see the little holes? Those are the bubbles of CO2 gas that was produced. The baking soda reacted with the acidic sour cream and the baking powder reacted with its different parts to make all those little holes.






Review:

Lets look back over the things we explored today. We learned that there are many things in our homes that are acids or bases. Then by making the coffee cake we saw how they can react together to produce gases and raise our cake (leavening). Did you like these experiments? In later experiments we can explore other ways to produce CO2 and leaven things. We can also find other exciting ways to use acids and bases.


Still need a challenge?

Lets take a look at the amount of CO2 that has been produced both as a volume and the weight of CO2.

We’ll start with this equation:

PV=nRT

Lets define some basic constants and use the equation to solve for the weight of CO2. Along the way we’ll measure the volume of the total gas produced. In the end you’ll be able to measure the weight of a CO2 bubble in the coffee cake!

P= pressure in atmospheres
V= volume in liters
n = number of moles or weight/molecular weight grams
R= Universal gas constant = 0.082 liter-atmospheres per degree mole
T = temperature in absolute degrees (Kelvins) or 273 + Celsius degrees
Carbon dioxide (CO2) has a molecular weight of 44 moles.

In this case we are interested in change in volume of a baked batter. We need to find the initial volume of batter and the final volume of product by marking the pan and measuring the water volume between the lines after cooking and removing product. Measure this in milliliters, most measuring cups have liters and milliliters on the opposite side from cups. (1 liter = 1000 milliliters)

Assume P is one atmosphere because most of us will perform this at or below 5000 ft elevation. Also assume the temperature is a little above room temperature at 25 C (77 F) then T = 25 + 273= 298 K.

Carbon dioxide (CO2) has a molecular weight of 44 moles.

Since n = weight/molecular weight or wt/MW then

PV = wtRT/MW can also be written as

MWPV = wtRT can also be written as
wt = MWPV/RT

Now we know MW = 44, P = 1 and we are measuring the volume change (final volume – initial volume) assuming that change is the gas released (none escapes)

And R = 0.082, T = 298

Then 44x 1x V/ 0.082x 298 = 1.8006 and converting the volume to ml (milliliters) it is approximately 0.0018.

And we get the approximate weight of gas in the bubbles as 0.0018 V = wt of CO2 in the bubbles (that’s all of the bubbles added together).

Suppose our volume of batter was 750 ml and after baking the volume of cake was 1300 ml. The gas volume is 1300 – 750 = 550 ml and the weight of carbon dioxide is 550 x .0018 = 0.99 g.

Because carbon dioxide weighs 44 g/mole we can calculate that we have 0.025 moles of gas in the bubbles. Measuring the size of a bubble you can calculate the volume (V=4/3 pi r-cubed) r must be in millimeters (mm) and then calculate the weight of gas in an average bubble the same way as above (0.0018 x volume in l).
What is happening at Scifood4kids next time?

We are going to explore who the look and smell affect how things taste. We will learn about the colors found in different foods, what happens when they are cooked, and how the affect taste. We will also look at (or maybe taste, because we might wear a blindfold) how smell contributes to the flavors in food. Check back soon for the next experiments!