Antacid Showdown: Which Antacid Best Neutralizes Stomach Acid?
Science Lab · Grade 9
Shared by a teacher · Free to use as a template on AssessmentWiz.
Type
science_lab
Pre Lab
Background: Your stomach makes hydrochloric acid to help digest food. When you have too much of it, you may feel heartburn or an upset stomach. People take an **antacid** to feel better. An antacid is a **base** that reacts with stomach **acid** and cancels it out. In today's lab, **vinegar** (acetic acid, CH₃COOH) will stand in for stomach acid, because it is much safer to handle.
Scientists measure how acidic or basic a solution is with the **pH** scale, which runs from 0 to 14. A pH below 7 is an **acid**, a pH of exactly 7 is **neutral** (pure water), and a pH above 7 is a **base**. When an acid and a base react, they produce water and a salt. This reaction is called **neutralization**. One example is baking soda reacting with vinegar: NaHCO₃ + CH₃COOH → NaCH₃COO + H₂O + CO₂. You cannot see pH directly, so we use an **indicator**, a substance that changes color depending on pH. Red cabbage juice is a natural indicator. It turns pink/red in acid, purple near neutral (about pH 7), and blue or green in base.
Why do some antacids work better than others? It depends on their chemistry, and that chemistry connects to the periodic table. Baking soda (NaHCO₃) contains sodium, a **Group 1** metal with 1 valence electron. Sodium loses that electron to form Na⁺, and each formula unit of baking soda neutralizes 1 H⁺ from acid. Tums (CaCO₃) and milk of magnesia (Mg(OH)₂) contain calcium and magnesium, **Group 2** metals with 2 valence electrons. They form Ca²⁺ and Mg²⁺, and each formula unit can neutralize 2 H⁺: Mg(OH)₂ + 2CH₃COOH → Mg(CH₃COO)₂ + 2H₂O. Alka-Seltzer is tricky. It contains baking soda, but it also contains citric acid and aspirin, which are acids. How much active ingredient is packed into each dose also matters. Today you will collect data and decide which antacid really wins.
Vocabulary
Term: pH
Definition: A scale from 0 to 14 that measures how acidic or basic a solution is. Below 7 is acidic, 7 is neutral, and above 7 is basic.
Term: Acid
Preview shown. The full assessment (all questions, answer key, and teacher notes) loads with the page.