Things that need to be explained beforehand:
Concentration: "For chemists concentration is a measurement of how much stuff
(or molecules) are dissolved in a liquid.
A visual example: What would taste sweeter, a tablespoon of sugar dissolved in
a glass of water, or a tablespoon of sugar dissolved in a bathtub? Which one
would be more concentrated?
Nutrition labels: The amount of sugar per cup would be a good indicator on how
much stuff is dissolved in that beverage and a good comparison to our results
later.
Research Question
Which beverage is more concentrated?
Discuss in groups: How would you design an experiment to find out which liquid
is more concentrated?
Materials
6 cups
6 liquids (recommended: light soda, dark soda, Gatorade, water, apple juice)
Balance
Print outs of Work Sheet
Six 100 mL Syringes
Sticky notes
Student Guide
Step 1
Make a heading called "Introduction" in your science notebook. Write down what
you learned about concentrations, nutrition labels, and how they relate to the
things we drink everyday.
Make a new heading called "Research Question" and write down the question we
are trying to answer with our experiment.
Make yet another heading called "Hypothesis." Make a prediction what you think
will be the most concentrated drink and write it down.
Step 2
The teacher will divide the class into 6 groups. Each group will be assigned one
beverage to study and do experiments on. After groups have been assigned go
get 2 plastic cups, your beverage, 2 sticky notes, and a syringe. Also make a
new heading in your science notebook called "Methods"
Step 3
Label one cup "Cup 1" and the other "Cup 2" with a sticky note. Also mention
which liquid it will contain. Place each cup on the electrical scale and record the
weight you measured in your science notebook like this:
Weight of cup 1 without liquid: _______________________ grams
Weight of cup 2 without liquid: _______________________ grams
Step 2
Measure out 100 mL of your liquid with a syringe. Make sure you get only few
bubbles in the syringe. Pour the contents into cup 1. Repeat for cup 2. Once
each cup has 100 mL of liquid measure it again with the electric scale and record
your results in your science notebook like this:.
Weight of cup 1 with liquid: _______________________ grams
Weight of cup 2 with liquid: _______________________ grams
Discuss in your group: How much would the liquid weigh without the cups? How
long do you think it will take to evaporate all the liquid? Write down your answers
into your science book.
Step 3
Draw a line that marks the top of the liquid on the outside of each cup. Then
place the cups in a good spot somewhere near the window. Make sure all groups
place their cups near the same spot, otherwise the results will not be valid for
each group. Now we have to wait for the water in each cup to evaporate.
In your science notebook, describe what you did so far. Make sure you mention
the date and time you started your experiment as well and how long you will wait
for the liquid to evaporate.
Step 4
Each day check how much of your liquid has evaporated, by drawing a line that
marks the top of your liquid that day. Also check if your substance still is a liquid
(Swirl it around. Does it still flow? Or is it turning gooey?)
Record both the date and your observations that day in your science notebook
under the "Data" heading.
Step 5 (One week later)
After one week all the water should have evaporated. Check your cups and
record your observations in your science notebook. Is there anything left in the
cup? Is it still a liquid? After you made your observations measure the cups with
an electronic scale and record the weight in your science notebook like this:
Weight of cup 1 after one week: _______________________ grams
Weight of cup 2 after one week: _______________________ grams
Discuss in your group: Do the cups weigh more now than before you put the
liquid in? How much more do they weight and why do you think that is? What is
the stuff left in the cups? How many grams of "stuff" was dissolved in your liquid?
Make a new heading in your science notebook called "Results" and write down
your answers and discussion.
Step 6
Collect the data from the other groups, and plot it in a bar graph. Review your
hypothesis. Were you correct or incorrect? Write this in your conclusion and (if
you were incorrect) explain why you think the experiment turned out the way it
did.