Alka Seltzer Particle Size Lab
Modified from http://www.alka-seltzer.com/asp/student_experiments_2.html#materials
Modified by Jeanne Nye, Lake Mills Area Schools, Institute for Chemical Education and Nanoscale Science
and Engineering Center, University of Wisconsin-Madison
Name _________________
Class Period ___
Challenge
You are in charge of designing a new medication. You’ve been asked to design a tablet
that will be both long-lasting and quick acting. To help you in this project you’ve
designed a lab to investigate whether the size of the particle will help you create a better
tablet.
Question
Therefore, the scientific question can be summarized as follows:
Is the rate of a chemical reaction affected by the physical size of the reactants?
Idea
To develop this lab you must keep the mass constant, the amount of matter in one tablet.
If you decrease the size of the particles in the given mass (for instance, crush one tablet),
you will increase the number of particles in that given mass. This means you’ll compare
reaction rates of Alka Seltzer tablets by varying one thing, the size of the particles.
Your prediction:
Which fizzes up faster, the tablet that is whole or the tablet that is broken up? ________
Which finishes fizzing first? _________
Materials
Note: All experiments should be done using original formula effervescent Alka-Seltzer.
3 Clear glasses
Room temperature water
3 Alka-Seltzer tablets
Mortar and pestle
Stopwatch
Procedure
Of course, put on your stylish safety goggles and get out all equipment.
A. Whole Tablet
1. Fill a clear glass with exactly 8 oz. of room temperature or lukewarm water.
2. Start the stop watch when you drop 1 whole Alka-Seltzer tablet into the water. Stop
timing when it is totally dissolved.
3. Measure and record the time to dissolve.
Whole Tablet _________ Seconds
B. Tablet Broken into ~8 Pieces
1. Place 1 Alka-Seltzer tablet onto a sheet of paper and break into approximately 8 pieces
of about equal size.
2. Fill a clear glass with exactly 8 oz. of room temperature or lukewarm water.
3. Start the stop watch when you slide broken tablet into the water from the sheet. Stop
timing when it is totally dissolved.
4. Measure and record the time to dissolve.
8 Pieces _________Seconds
C. Powdered Tablet
1. Place 1 Alka-Seltzer tablet into mortar and grind to a fine powder.
2. Transfer powder into a clear cup. (Note: It's important to have the powder in the cup
before adding water.)
3. Start the stop watch when you add 8 oz. of water to the glass. Stop timing when it is
totally dissolved.
4. Measure and record the time to dissolve.
Powder _________Seconds
Observations
Summary: Particle Size Time for Reaction to be Completed
Whole Tablet _________ Seconds
8 Pieces
_________Seconds
Powder
_________Seconds
Summary
a) As particle size decreases, the rate of reaction ________________________
(increases, decreases or stays the same).
b) The rate of reaction for the powder was ___________ times faster than for the whole
tablet.
Questions
1. As particle size decreases, the total surface area of a reactant ________________
(increases, decreases or stays the same).
2. As a result, the probability of interactions between atoms/ions ________________
(increases, decreases or stays the same), and the rate of reaction ___________________
(increases, decreases or stays the same).
3. Particle size appears to have _______________ (no impact, some impact, a great
impact) on the rate of reaction.
Application Questions
1. Using your results, as you design your long-lasting medication, which size particle
will you prefer? __________________
2. Using your results, as you design your quick-acting medication, which size particle
will you prefer?
3. Describe your new quick-acting, long-lasting tablet.
_________________________________
________________________________________________________________________
________________________________________________________________________
____________
4. Using your data consider the environmental impact. Which is more likely to impact
the environment, a quick acting tablet or a long-lasting tablet? __________________
Why?
_______________________________________________________________________
________________________________________________________________________
______
Teacher Information
What’s going on?
The crushed tablet fizzes faster than the whole tablet. That’s because it has a greater
surface area to volume ratio. That means that for the same amount of antacid (one
tablet), there is more surface—or exterior—to react with the water. Because the water
can reach more of the antacid immediately, the chemical reaction (fizzing) happens
faster.
Small things have a greater surface area to volume ratio than larger things do. Some
things that aren’t reactive at all in big pieces are very reactive when they’re tiny. Steel
wool catches fire, but you can’t easily light a lump of metal on fire!
How is this nano?
The greater reactivity of small things is important in nanotechnology, because it means
that nano-sized things react much more easily and quickly than they would if they were
larger.