St. Patrick’s Day Science: Brew up Some Green Soda Pop!
Have you ever wanted to make your own soda pop? Even if you haven’t, maybe as a treat on a relaxing afternoon you like to open a can of your favorite carbonated beverage and take a deep drink. The bubbles in the soda tickle your tongue’s taste buds and propel the ingredients to your palate and nose so that you get a kick of flavor. But how do the bubbles, fizz and taste get into the water? In this tasty science activity, you will work with baking soda, citric acid and sugar to create your own soda pop! After you develop your recipe, add a few drops of green food coloring and you’ve got a festive drink you could share with friends and family to celebrate St. Patrick’s Day together!
Soda pop is essentially carbonated water with sugar added. Carbonated water is water into which a gas called carbon dioxide has been dissolved under high pressure. When you open a can or bottle of soda, the pressure is released and the carbon dioxide starts to come out of the solution. The escaping carbon dioxide is what causes the bubbles in the beverage. Carbonation also occurs in nature, when water underground comes in contact with a source of carbon, such as limestone. The reaction between the water, limestone and the high pressure of the earth creates carbon dioxide that becomes dissolved into the water. When the water eventually rises to Earth’s surface, the pressure is released and bubbly water is the result.
In this science activity, you’ll use baking soda (also called sodium bicarbonate), citric acid and sugar to develop your own recipe for soda pop. When you mix baking soda and citric acid together with water, a chemical reaction takes place that creates carbon dioxide, along with sodium citrate. Sodium citrate, like the others you’ll be using in this activity, is a harmless substance that’s safe to eat or drink.
- At least five cups
- Baking soda
- Citric acid
- Green food coloring
- Spoon or fork for stirring
- Measuring spoons
- Measuring cup
- Measure out and add 1/4 teaspoon (tsp.) of citric acid to three of your cups. (Leave two cups empty.)
- To one of the cups with citric acid in it, add 1/16 tsp. baking soda. (Measure 1/16 tsp. by filling a 1/8 tsp. measuring spoon half full.)
- Add ¼ cup of cool water to the cup with citric acid and baking soda in it, mixing them together with a spoon or fork. Are there a lot of bubbles? Is the liquid mildly bubbly or is it bubbling a lot?
- Taste a little bit of the beverage. How does it feel on your tongue? Is it too gritty? Do you find the feeling of the liquid in your mouth pleasant?
- After tasting the beverage, feel free to spit out the liquid (into one of the empty cups). It will not harm you to swallow it, but it might not taste very much like soda yet (mostly because sugar has not yet been added), and you also don’t want to over-acidify your stomach (which could give you a slight stomachache) because there is still more taste testing to do.
- To one of the two remaining cups with citric acid in it, add and mix together ¼ tsp. baking soda and ¼ cup of cool water. Are there more or less bubbles with this mixture?
- Again taste a little bit of the beverage. How does it feel on your tongue? Is it gritty, or do you find the feeling to be pleasant? Again, feel free to spit out the liquid after tasting it.
- To the last cup with citric acid in it, add and mix together one tsp. baking soda and ¼ cup of cool water. Are there more or less bubbles with this mixture?
- Again taste some of the beverage. How does it feel on your tongue? Is it gritty or pleasant? Again, feel free to spit it out afterwards.
- Decide which recipe you enjoyed the best. Make up a fresh quarter cup of it (the same way you made it before). Then mix in ¼ tsp. of sugar. How does it taste? Does it taste like a soda pop?
- Continue to mix in ¼ tsp. of sugar at a time, tasting it after you add the sugar each time, and add no more than 1 tsp. sugar total. What amount of added sugar makes for the tastiest soda pop?
- After you’ve decided how much sugar to add to your baking soda and citric acid mixture, you can scale up the recipe to make a festive, green-colored beverage! For example, if you found that 1/4 tsp. baking soda and ¼ tsp. sugar worked well in ¼ cup, you could make one cup of soda with 1 tsp. baking soda, 1 tsp. sugar, and 1 tsp. citric acid. Then mix in just three drops of green food coloring, and you festive beverage is ready to enjoy!
Extra: Ask your friends and family to taste the final recipe that you developed. Do they enjoy the beverage as much as you do? Collect their feedback and see if you can develop a recipe that everyone enjoys. You could even try adding flavorings, such as vanilla, cinnamon or a little bit of crushed fruit.
Extra: Do this activity again but test a wider variety of baking soda and citric acid recipes (such as including 1/8 tsp. and ½ tsp. baking soda recipes). Then try to numerically rank (such as on a scale of 1 to 5) how gritty and bubbly each combination is. Which recipe makes the bubbliest soda pop? What about the least gritty one? Overall, which recipe is best?
Extra: Some fruits contain citric acid. Try recreating your soda recipe using fruit juice from a fruit that contains citric acid, instead of using food-grade citric acid. How does the amount of fruit juice compare to the quantity of food-grade citric acid in your ideal flavor combination?
Observations and Results
Was the recipe that used ¼ tsp. baking soda and ½ tsp. sugar the best, tasting the most like a normal soda pop?
In this activity, when you mixed together baking soda and citric acid (with water), the chemical reaction should have made fizzy carbon dioxide bubbles, making all of the recipes you tested produce at least some bubbles. The recipe with the least amount of baking soda added (1/16 tsp.) should have made the fewest, shortest-lived bubbles, while the recipe with the most baking soda (1 tsp.) should have been clearly the fizziest. This is because there is more baking soda available to react with the citric acid, making carbon dioxide bubbles. However, the recipe with 1 tsp. baking soda was likely rather gritty and bitter, due to the large amount of baking soda. This probably made the recipe using ¼ tsp. baking soda the ideal recipe in terms of bubbliness, flavor and texture. You may also have found that adding ½ tsp. of sugar was the ideal amount, but this can vary based on personal preference.
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- Introduction to Pop - The History of Soft Drinks, from About.com
- Shimmy, Shimmy Soda Pop: Develop Your Own Soda Pop Recipe, from Science Buddies
- Science Activities for All Ages!, from Science Buddies