Teaching Elementary School Science
The Wayward Raisin (a.k.a Sewer Lice)
Essential Concepts & Skills: Iowa Core, Grades 3-5
● Identify and generate questions that can be answered through experiments.
(Science as Inquiry)
● Uses evidence to develop a reasonable explanations (Science as Inquiry)
● Communicate procedures and explanations (Science as Inquiry)
● Work productively and are accountable for their actions (21st Century Skills Employability)
● Develop initiative and demonstrate self-direction in activities (21st Century Skills Employability)
What students will be doing: Students will be learning how to make detailed
observations of floating and sinking raisins and will use those observations to try
to explain what is happening.
Materials:
1 graduated cylinder per group (100 mL)
tap water (100 ml)
vinegar (25 - 50 mL per group)
baking soda (4-6 tsp per group)
raisins (3)
lunch trays
plastic spoons
safety goggles
colander (for dumping used vinegar in so items don’t go down the drain)
other items to experiment with (i.e., rice, popcorn kernels, beans, beads, paper
clips, clay)
Note: It is best to have baking soda and vinegar in small containers already placed
on the lunch trays. Make sure you review clean-up procedures before
students begin experimenting.
Safety: While vinegar is a pretty weak acid, it will sting if it splashes in
students’ eyes. Thus it is best to stress safety and insist all students wear
goggles until they are done experimenting and all materials have been cleaned up
and put away.
Introducing the Activity
“In this activity you will be fine tuning your skills at observing. Who can tell me
what that means? In science, observations are not always made by your eyes.
Other senses can be used too. (Ask them to recall the other senses and have them
come up with examples where they used each sense to make an “observation”.)
This activity is a puzzle - you have to try to figure out WHY things are
happening and the only way to figure this out is to make careful observations of
every little thing you see. If you miss something, you are not likely to be able to
figure out WHY things are happening. Like all good scientists, you will need to
write down what you see.” Then explain how you want them to work in groups,
take turns with mixing and with clean-up and will show them how their table and
tray should look at the end of the period.
Verbal Directions for Students:
Before starting, get your goggles on. You will be using a graduated cylinder to
measure out 50 mL of water. Pour the water into a plastic cup and add 2
teaspoons of baking soda. Stir the baking soda until it dissolves. Pour this
solution back into the 100 mL graduated cylinder. Next measure out 25 mL of
vinegar and slowly add it to the cylinder. Immediately drop the raisins into the
cylinder. Closely observe what happens. It may take several minutes for a
change to occur, so be patient! Record all of your observations in the space
provided. Remember, a scientist must be very observant! If the raisins slow
down after a while, stir the liquid or add a bit more vinegar or water-baking soda
mixture. You might need to experiment with amounts of each ingredient to get
the best bobbing raisins.
Write the abbreviated directions on the board or overhead:
Place everything on the tray
50 mL of water into a plastic cup + 2 tsp baking soda (stirred)
Place this mixture in the graduated cylinder
Measure 25 mL vinegar in another graduated cylinder
SLOWLY add the vinegar to the water-baking soda mixture
Drop in a few raisins and record everything you observe
Teacher Notes:
This activity generates a lot of excitement among students. Stress the
importance of doing the entire experiment on the tray. (Students will be excited
when they see that their vinegar, water and baking soda combination may foam
over the top of their cylinder. This is OK, but can be prevented by adding
ingredients slowly. Make sure students are actually recording their
observations. Circulate around the room keeping an eye out for good
experimental techniques and for students who may be using the materials
inappropriately.
In the end, it is important that students list their observations in the correct
order, as this is the key to developing a correct explanation.
Sample student explanation: The raisin is added to the liquid/baking soda and
sinks to the bottom of the cylinder. As it sits on the bottom, bubbles begin to
form on the sides of the raisin. Eventually, there are so many bubbles on the
raisin, that it begins to float to the top. Once it gets to the surface, the bubbles
on the sides of the raisin begin to pop and sink to the bottom again. Once at the
bottom more bubbles form on the raisin and the cycle starts again. Students are
likely to say that the cause of the floating and sinking raisin is that the bubbles
cause the raisin to float and when they are gone, the raisins sink. For this grade
level, this is likely an adequate explanation. In fact, the floating and sinking is
related to the concept of density. The bubbles cause the density of the raisins
to decrease to a value less than that of the liquid, so they float. Density = the
size of the raison divided by its mass. The bubbles make the size bigger without
changing the mass, thus the density of the raisin decreases.
Student Worksheet
The Wayward Raisin
Group Members: ___________________________________________________________
Write 10 observations about the details of what you see happening.
1
2
3
4
5
6
7
8
9
10
Put in one fresh raisin. Write down everything that happens to the
raisin from the second you drop it in the liquid until it starts doing the
same thing over again. No explanations please. Include every detail!
first
second
third
fourth
fifth
sixth
sevent
h
Do you think other objects might behave the same way a raisin does?
Your teacher will give you some items you can try. Select some items
to test, try them and write about what happens. If you have ideas for
any other items to test, check with your teacher first, then test them.
Be sure to record what happens.
Test Items
Description of What Happens
Summarize your data: Based on the extra objects you tested, what
characteristics does an object have to have to do the best floating and
sinking?
The best wayward raisins (sewer lice) have these
characteristics . . .
Conclusions: Based on all of your observations of the raisins and
other objects, write an explanation of what is causing the raisin to
repeatedly rise and sink.
Sample Student Responses
The Wayward Raisin
Group Members: ___________________________________________________________
Write 10 observations about the details of what you see happening.
1
The raisins sink to the bottom
2
They stay on the bottom, but seem to be moving around.
3
Bubbles are rising to the top of the liquid.
4
Bubbles are sticking to the sides of the raisin.
5
The raisin rotates around when it goes to the top.
6
The raisin stays on the top for a few seconds, then it goes back
down.
7
The bubbling gets less after a while and eventually stops.
8
You can hear the bubbles.
9
Some raisins get buried at the bottom in the baking soda.
10
More than one raisin can work.
Put in one fresh raisin. Write down everything that happens to the
raisin from the second you drop it in the liquid until it starts doing the
same thing over again. No explanations please. Include every detail!
first
The raisin falls to the bottom.
second
Bubbles start to form on the outside of the raisin.
third
The raisin starts to rise toward the top.
fourth
The raisin hit the top of the liquid and some of the bubbles
pop.
fifth
The raisin then sinks to the bottom again.
sixth
More bubbles form on the outside of the raisin.
sevent
h
The raisin goes to the top and everything starts over again.
Do you think other objects might behave the same way a raisin does?
Your teacher will give you some items you can try. Select some items
to test, try them and write about what happens. If you have ideas for
any other items to test, check with your teacher first, then test them.
Be sure to record what happens.
Test Items
Description of What Happens
popcorn kernels
Works like the raisin. It floats up & down.
paper clips
Sinks to the bottom and stays there.
lentils
A couple of them worked, then they stopped.
rice pieces
Sinks and floats for a while.
penny
Sinks to the bottom and stays there.
plastic beads
Sinks to the bottom and stays there.
ball of clay
Sinks to the bottom and stays there.
smashed piece of
clay
If I get it just right, it works like the raisin and
goes up and down.
Styrofoam
Does not work because it never sinks.
Summarize your data: Based on the extra objects you tested, what
characteristics does an object have to have to do the best floating and
sinking?
The best wayward raisins (sewer lice) have these
characteristics . .
wrinkled surface
not too heavy
must be able to sink
must have a lot of surface (like the smashed clay)
Conclusions: Bubbles must be able to form on the outside of the
object. The bubbles carry the object to the top, then the bubbles
break so it falls back down. Science-wise, the bubbles forming on the
outside of the object causes it volume (size) to get bigger while its
mass remains essentially the same. Since density is mass divided by
size, the bubbles make it less dense, so it floats. Elementary children
will not come to a conclusion of this detail, nor should they be
expected to. If students can conclude that the bubbles are causing the
object to rise, that is sufficient.