Key concepts
Chemistry
Acids
Bases
Ions
Reactions
Introduction
Did you know that the juices in your stomach are nearly as acidic as lemon juice? Fortunately, your stomach has special cells that act as a barrier to the acid, preventing it from breaking down your stomach tissue. These cells produce a basic mucus that neutralizes the acid in your stomach. It turns out that your stomach is a pretty sophisticated chemistry laboratory!
In this activity you'll explore a delicious acid-base reaction, this time using your mouth as the chemistry lab!
Background
We use acids and bases every day—they’re present in our foods, our cosmetics and our cleaning supplies. We’re so used to them that it’s easy to forget how interesting they are and how much our daily activities depend on the reactions they generate.
An acid is a compound that is capable of donating a positively charged hydrogen ion (or proton). If you add an acid to water, it breaks apart and makes the solution more acidic by adding hydrogen ions. Acids come in many different strengths and are essential to our daily lives. We couldn’t digest our food without the acid in our stomachs!
Bases are also extremely important in our lives. A base is a compound capable of donating negatively charged hydroxide ions. If you add a base to water, it breaks apart and makes the solution more basic by adding hydroxide ions.
When acids and bases are combined an acid-base reaction occurs. If there are an equal number of hydrogen and hydroxide ions present, the acid and base will neutralize each other, forming a salt and water. In this activity you will explore the reaction that takes place when you combine an acid with a basic carbonate. The product of this reaction is a fun and tasty surprise!
Materials
- Three small, sealable plastic sandwich bags
- Six tablespoons confectioners sugar
- Nine tablespoons gelatin crystals (the flavored kind works best)
- Two teaspoons baking soda
- Two teaspoons citric acid (available in the spice/baking section)
- Permanent marker
- Measuring spoon (teaspoon and tablespoon)
- Regular spoon
- Glass of drinking water
Preparation
- Use your marker to label your bags. Label bag one: "Acid + Soda"; bag two: "Acid Only"; and bag three: "Soda Only."
Procedure
- Carefully measure and add two tablespoons of confectioners sugar to each bag.
- Carefully measure and add three tablespoons of gelatin crystals to each bag.
- Add one teaspoon of citric acid to the bag labeled "Acid + Soda." Add another teaspoon of citric acid to the bag labeled "Acid Only."
- Add one teaspoon of baking soda to the bag labeled "Acid + Soda." Add another teaspoon of baking soda to the bag labeled "Soda Only."
- Seal each bag, then shake them to mix the ingredients together. Does anything happen to the ingredients when you mix them together? Is there any kind of reaction that you can observe?
- Once the ingredients are well mixed open the bag labeled "Acid Only." Use your spoon to take a small scoop of the bag contents and put them in your mouth. Hold the ingredients on your tongue for a moment before swallowing them. What does it taste like? Can you feel anything happening in your mouth when you taste them?
- Take a drink of water and rinse your mouth thoroughly.
- Open the bag labeled "Acid + Soda." Use your spoon to take a small scoop of the bag contents and put them in your mouth. Hold the ingredients on your tongue for a moment before swallowing them. What does it taste like? Do you notice anything different about this taste test, compared to the "Acid Only" bag? What is different?
- Take a drink of water and rinse your mouth thoroughly.
- Open the bag labeled "Soda Only." Use your spoon to take a small scoop of the bag contents and put them in your mouth. Hold the ingredients on your tongue for a moment before swallowing them. What does it taste like? Which taste test is this most similar to, the first one, or the second one?
- Extra: Try changing the proportion of ingredients, adding half a teaspoon more acid or soda, and see how it changes the reaction.
Observations and results
In this activity your mouth was a mini-chemistry lab! When you tasted the "Acid + Soda" bag contents, you should have felt a fizzing or popping sensation in your mouth. When the acid (citric acid) and carbonate base (baking soda) mixed with your saliva, a chemical reaction took place that created carbon dioxide gas—which you felt as tiny bubbles in your mouth. The dry ingredients also react with each other, but it’s a much slower reaction. When you add them to your mouth, the saliva helps the acid and base dissolve, increasing the chances that a bicarbonate ion will come in contact with an acidic proton. The reaction, therefore, takes place much more quickly, and you can feel the gas bubbles produced!
An acid-base reaction like this one requires two main ingredients—can you guess what they are? An acid and a base! So when you tasted the contents of the "Acid Only" or the "Base Only" bag you shouldn’t have felt any chemical reaction occur. In both cases you were missing a critical ingredient. With the "Acid Only" bag you had citric acid but no baking soda, therefore the acid didn’t have a base to react with. In the case of the "Base Only" bag, the baking soda did not have an acid to react with.
You might have also noticed that each bag tasted slightly different. Baking soda is a salt; it is also called sodium bicarbonate. You might have noticed that the "Soda Only" bag tasted slightly saltier than the other two bags. Acids such as citric acid, in contrast, often taste sour to us (think about citrus fruits with high citric acid content, such as lemons, limes and grapefruit). You might, therefore, have noticed that the "Acid Only" bag tasted more sour than the other two bags.
More to explore
Bath Bomb Science, from Science Buddies
Shimmy, Shimmy Soda Pop: Develop Your Own Soda Pop Recipe, from Science Buddies
Cabbage Chemistry: Finding Acids and Bases, from Scientific American
Science Activities for All Ages!, from Science Buddies
This activity brought to you in partnership with Science Buddies
