An acid is like a sour superhero, let’s call him Acidus, that loves to give away tiny pieces called protons (or H⁺ pieces). The stronger he is, the more protons he can donate as H+. This increased concentration of H+ ions in water makes a solution acidic.
So, in Chemistry, an acid is a substance that increases the concentration of hydrogen ions (H⁺) in water.
Remember the sour taste in lemons? Did you know that the lemon juice contains citric acid, a weak organic acid capable of donating up to three hydrogen ions (H⁺) per molecule in water?
Below is a super simple experiment to explore the concept of an acid in real life. We aim to prove that lemon juice is acidic and that when it is mixed with a baking soda, it can react!
Lemon Juice & Baking Soda Experiment
Materials needed:
Fresh lemon or lemon juice (contains citric acid)
Baking soda (sodium bicarbonate)
A clear glass or container
Water
Spoon
Procedure:
Pour some lemon juice into the glass (or squeeze a fresh lemon).
Add a little water to dilute it—this simulates an aqueous solution.
Sprinkle a spoonful of baking soda into the lemon juice.
Observe the reaction
Observation: Fizzing and bubbling occurs!
Why it works: When citric acid dissolves in water, the polar molecules of water interact with citric acid, an interaction that pulls apart the hydrogen atoms bonded to oxygen in the acid. It's a triprotic acid, meaning it can donate up to three hydrogen ions (H⁺) per molecule in water.
The hydrogen atoms, due to being tugged away by the water molecules, slowly lose their attachment with the citric acid molecule and become free-floating hydrogen ions (H+, protons) in solution. These newly formed H⁺ Ions make the solution acidic. But because it’s a weak acid, only a fraction of the citric acid molecules fully donates H⁺ ions. That’s why lemon juice has a sour taste but isn’t corrosive enough to burn your mouth like strong acids (e.g., hydrochloric acid).
The baking soda acts as an acceptor of H+ ions. Their reaction produces carbon dioxide gas—hence the fizz! This release of gas is a direct result of acid-base neutralization.
Bonus Tip: Try comparing the reaction using vinegar or orange juice and notice differences in intensity—that's acidity in action!
Related Content – Three types of Acids in Organic chemistry