Key Concepts
Acids, bases, acid-base reaction

Introduction

Did you know that the soda company Coca-Cola makes over 3,500 different types of soda to distribute around the world? If you tried a different one every day, it would take you over 9 years to try them all! Do you think you would like octopus-flavored soda? What about cheese-flavored soda? If you travel far enough around the world, you’ll find those and many other flavors that may seem exotic in the U.S. Although the flavors might differ, one thing that all sodas have in common is the bubbles! Soda isn’t soda without that fizz, but have you ever wondered how they create those bubbles? In this activity you will make your own bubbly drink, while exploring the reactions that create that famous fizz. Bottoms up!

This activity is not appropriate for use as a science fair project. Good science fair projects have a stronger focus on controlling variables, taking accurate measurements, and analyzing data. To find a science fair project that is just right for you, browse our library of over 1,200 Science Fair Project Ideas or use the Topic Selection Wizard to get a personalized project recommendation.

Background

Acids and bases are all around us; in our dishwashing liquid, our medicines, even our foods!  We keep them around us because they’re extremely useful, in part because they react so strongly to each other. We can use these reactions to help us clean, ease a sick stomach, and make food taste more interesting.

As you may know, a base is a compound that can donate negatively charged hydroxide ions. When you add a base to water, the basic compound will break apart, making the solution more basic with the addition of its hydroxide ions. Bases are found in many household cleaning supplies, as well as in medicine to help neutralize stomach acid for people who suffer from heartburn.

In contrast, an acid is a compound that can donate a positively charged hydrogen ion (or proton). When you add an acid to water, the acid will come apart, making the solution more acidic with the addition of its hydrogen ions. While acids can be dangerous, we also need them to survive. The acid in our saliva helps break up food as we chew! 

When you combine an acid and a base, you initiate an acid-base reaction. When 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.

Materials

  • Cold Water
  • 2 lemons
  • 1 teaspoon sugar (more or less to taste)
  • 1 teaspoon baking soda
  • A plastic or glass cup
  • A stirring spoon
  • A lemon juicer/press (recommended)
  • An adult helper
  • A knife for slicing lemons
  • Ice (optional)

Procedure

  1. Have your adult helper cut both lemons in half.
  2. Use the lemon juicer to squeeze all of the juice from each lemon into your glass. Taste a few drops of the lemon juice. How would you describe the taste?
  3. Add an equal amount of cold water to the lemon juice in your glass. Taste the mixture again. Does it taste different than just the lemon juice? In what way?
  4. Carefully add one teaspoon of baking soda. Use your spoon to stir the mixture. What happens when you add baking soda to the lemon juice? What do you see and hear happening in the glass?
  5. Use your spoon to stir one teaspoon of sugar into the mixture. Add ice if you want it cold!
  6. Taste your concoction! What do you notice about the taste? How does it differ from the lemon juice alone?
Extra: Allow your mixture to sit for an hour, then taste it again. How has the taste changed over the course of the hour? Why do you think this change occurred?

Observations and Results

In this activity you should have observed a ‘fizzing’ or bubbling when you added the baking soda to your lemon juice mixture. In addition, when you tasted your final product, you should have also been able to feel the bubbles in your mouth. The bubbles you felt in your mouth were the product of an acid + base reaction. Can you guess which of the ingredients in your mixture was the acid, and which was the base?

If you predicted that the lemon juice was the acid – you’re right! You can recognize acidic foods (like lemons, which are very acidic) based on their taste – acids taste very sour to us. Other acidic foods include vinegar, grapefruit and limes! Bases on the other hand can be more difficult to detect. Basic foods can taste slightly bitter to us, or they may have very little taste at all. In this case, the base in this mixture was the baking soda. Baking soda doesn’t have much of a taste, but you may have guessed that it was the base in your reaction, because as soon as you added it, your mixture should have started fizzing!

When the acid of the lemon juice (citric acid) came in contact with the carbonate base (baking soda) a chemical reaction took place, creating carbon dioxide gas (CO2). As you may know, CO2 is the same gas that is added to sodas to give them their fizz.

This reaction requires both an acid and a base in order to take place, therefore when you tasted just the lemon juice or the lemon juice + water mixture, you shouldn’t have noticed any bubbles. Water is generally neutral (not an acid or a base) therefore adding it to your lemon juice did not produce the reaction needed to create CO2 bubbles. It wasn’t until you added the baking soda that the reaction took place, and the bubbles were created.

More to Explore

Shimmy, Shimmy Soda Pop: Develop Your Own Soda Pop Recipe by Science Buddies

Bath Bomb Science by Science Buddies

Science Activities for All Ages! from Science Buddies

Credits

Megan Arnett, PhD, Science Buddies

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Key Concepts
Acids, bases, acid-base reaction
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