University of Florida Chemistry Outreach Program
Adhesion Lab
Estimated Time: 35 mins. + 15 mins. clean-up
Topics: Adhesion properties, Making a “sticky” paste, SC.H.1.3
Introduction: What is it that makes a substance sticky? Adhesion is a quality that has intrigued scientists for
decades. Although chemists will explain bonding between atoms with intermolecular forces (IMFs),
acid/base relationships, and charge density differences, adhesion can also exist through mechanical
relationships (such as Velcro® devices) and physical forces (such as electrostatics). The study of
adhesives can be brought down to a basic level using everyday household items and small quantities
of water.
Objective: This lab will teach students that different substances will exhibit differing adhesive properties when
combined with small quantities of water. This is due to the unique chemical properties of each
substance, and students will employ elementary scientific methods to “empirically” determine which
among a set of household items will work as the ‘best’ adhesive. Students will also learn how to
make solutions based on qualitative descriptions.
Materials: -Salt
-3x5 index cards
-Sugar
-Trays
-Cornstarch
-Stopwatches
-Flour
-Cups
-Water
-Popsicle sticks
-Assortment of small dice or plastic cubes (different colors work best)
Safety:
-Remind students there is NO eating or drinking in the lab.
-The small cubes are a possible choke hazard.
-All spills should be cleaned up immediately.
Procedure:
1. Prior to the start of the lab, the UF volunteer team should briefly review principles of adhesion (see
discussion section), explaining exactly what adhesion is (“stickiness”) and covering the basic
mechanical, physical, and chemical explanations for the phenomenon. Examples should be used
frequently to better illustrate concepts (for example, for surface area adhesion, a volunteer could
show how “wet paper is ‘stickier’ than dry paper”).
2. Students, working in pairs (or groups of three) will be stationed at lab areas that are equipped with
four cups, one each for (dry) salt, sugar, cornstarch and flour (a few tablespoons of the substance in
its respective cup is adequate). The lab area should also contain a cup of water, four popsicle sticks
(one for each cup), four plastic cubes/dice (of different colors, if possible), one 3x5 index card, and a
stopwatch.
3. Students will be instructed on how to make a “paste” with each of their substances. They should be
told that only a little water should be added to each cup, such that the substances within do not
dissolve, but instead form a thick, pasty derivative.
4. Students should use one of the popsicle sticks to apply a small amount of one of the pastes to one of
the plastic cubes/dice. An approximately equal amount of the other pastes should be added similarly
using different popsicle sticks and onto their own plastic cubes/dice.
5. Immediately after applying the paste, students should affix the plastic cube/dice to their 3x5 index
card. One student should then invert the card while the other starts the stopwatch.
6. Students should record the length of time it takes for each cube to fall from the index card.
Procedure (cont.):
7. Based on the results, students should conclude which paste proved to be their “best” adhesive. These
results should be compiled on the chalkboard, and discussion can ensue.
8. UF volunteers should explain any anomalies in the measured results, and try to account for them.
Procedural Note: If colored dice/plastic cubes are unavailable, it may be difficult for students to determine the
correct paste to which a falling cube corresponds. In this situation, the procedure may be adjusted
such that each cube is measured separately of the others (with the stopwatch) or numbered labels can
be placed on both the pastes and the cubes themselves.
Discussion:
1. Why was cornstarch a less effective adhesive when compared to flour?
2. What effect does drying/evaporation of the water in a paste have upon its adhesive qualities?
3. How does superglue work?
Adhesion can be addressed through mechanical, physical, and chemical explanations. Mechanical
adhesives, such as Velcro, employ minute fibers (shaped like small hooks) that lock upon contact
with a similarly surfaced substance. On the other hand, a physical-force adhesion is observed with
the electrostatic theory; this is of course best illustrated with a balloon that has been statically
charged and then brought into contact with a sweater, hair, or similar surface. Chemical explanations
for adhesion are much more complex, and can span basic atomic theory (ionic, covalent, or hydrogen
bonding), simple charge differences (+ vs. – charged attractions), and the concept of polarity.
Superglue (cyanoacrylate) works by reacting with the hydroxyl ions present in water; since virtually
every surface contains trace amount of water, superglue will effectively bind any two together
(acetone can dissolve the bond). Superglue works differently from more traditional glues, such as
Elmer’s, which is an adhesive by evaporation. As the water content of the glue evaporates (“letting
the glue dry”), the surfaces in contact will remain adhered together.
Source:
This lab is a modified version of a similar activity from a GEMS manual.