Antacid Tablet Race
TOPIC: Rocket fuels and propellants
Objective: To demonstrate how increasing the surface area of a chemical increases its reaction rate.
Description: A whole antacid tablet and a crushed tablet are added to separate beakers of water so that their relative reaction rates can be compared.
EDITED BY: Roger Storm, NASA Glenn Research Center
 Materials:
- Antacid tablets (two per test)
- Two beakers (or glass or plastic jars)
- Tweezers or forceps
- Scrap paper
- Watch or clock with second hand
- Small block of wood
Procedure:
- Fill both beakers about half full with water of the same temperature.
- Wrap paper around one antacid tablet. Place the packet on a hard surface and crush the tablet by pressing on it with the wood block.
- Open the paper packet with the crushed tablet and hold it over one of the beakers. Pour the powder in the water and time how long it takes for the powder to dissolve.
- Pick up a whole tablet and drop it into the second beaker of water. Time how long it takes to dissolve completely.
Discussion: This activity demonstrates how increasing the surface area of an antacid tablet by crushing it into a powder increases the rate in which it dissolves in water. This is a similar situation to the way the thrust of a rocket is increased by increasing the burning surface of its propellants. Increasing the burning surface increases its burning rate since more fuel becomes exposed to oxygen . In solid rockets, a hollow core extending the length of the propellant will permit more propellant to burn at a time. This increases the acceleration of the gases produced as they leave the rocket engine. Liquid propellants are sprayed into the combustion chamber of a liquid propellant rocket to increase their surface area. Smaller droplets react more quickly than do large ones, increasing the acceleration of the escaping gases.
Teaching Notes and Questions:
- This activity is an ideal way for safely showing how the burning rate of rocket propellants is increased without having the students use fire.
- A similar activity can be tried with small pieces of hard candy. Take two pieces of candy and crush one. Then, give the whole candy piece to one student and the crushed candy to another student to dissolve in their mouths. Which candy will dissolve first?
- Demonstrate the same effect by trying to ignite a thick piece of wood with a match. Next, cut the wood with a sharp knife to make shavings. Then, try to ignite the shavings. Caution: Be sure to exercise proper safety precautions with fire.
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