Measuring
Mass, Fluid Volumes, and Concentrations
Teacher’s Instructions
Purpose: The
purpose of this experiment is to help the students appreciate the relationship
between mass, volume and concentration, and between actual and estimated
values.
Note: We
have found, with the help of a food technology laboratory, that a typical
packet of Sweetened Cherry KoolAid has a mass of approximately 3.6 grams.
The Red Dye #40 within the powder, which we will use as the "indicator"
in the experiment weighs 960 mg/kg or 3.456 milligrams. To make the calculations
simpler, we use 3.4 mg = mass of the indicator.
Suggestion:
When designing this experiment we had in mind that you, the teachers,
would divide the class into groups. This experiment is designed to be
flexible given each teacher’s available supply of beakers, fish tanks,
etc. So, you may modify our setup given your number of students and available
resources.
Materials for the entire class:

1 irregular shaped container
(that holds greater than 1 L of water)
 4 packets Cherry KoolAid
sweetened (net mass of package should be approximately 3.6 g)
 masking tape
 markers
 calculators
Materials for each group:
 1 five gallon aquarium
 1 100 mL beaker (or other
container capable of holding at least 100 mL of water)
 1 1000 mL beaker (or
other container capable of holding at least 1 L of water)
 3 packets Cherry KoolAid
sweetened (net mass of package should be approximately 3.6 g)
 2stirring rods
 1 large wooden spoon
or something to stir KoolAid into solution in the fish tank
Teacher Setup:
1.) Label the 100mL beaker
as container "A" using the
masking tape and marker. Label the 1L beaker as "B,"
the fish tank as "C" and the
unknown container as "Unknown."
2.) Fill the Unknown
container with an amount of water greater than 1L, make sure that you
measure this amount and do not share this value with the students, yet.
Also, mix 24 KoolAid packets into the Unknown
container and calculate the concentration of the indicator in the solution
you just made. Do not share this with the students until they get to Part
3.
Student Setup:
3.) Have the students
fill container A with
100 mL of water, container B
with 1000 mL of water and container C
with 10 L of water (you
may want to do this given time constraints).
4.) Have the students put one
packet each of Cherry KoolAid in containers A,
B and
C and mix thoroughly so that no
KoolAid settles to the bottom of the containers.
Part 1 Determining Concentrations:
5.) Have the students
fill out Part 1 of the student journal activity sheets, which asks
for the mass of the indicator, volume of the solution and concentration
of the indicator in containers A, B
and C.
Also, have them rate the concentration of the solution qualitatively by
describing the color of the solution (i.e. bright red, red, light red, orange,
pink, etc)
The indicator mass for all
three is 3.4 mg. The volume is either 100 mL, 1000 mL (1 L), or 10 L,
depending upon the container. The concentrations, therefore for A, B
and C, respectively, should be 34 mg/L, 3.4 mg/L and .34 mg/L.
Part 2 Estimating Volume and
Concentration
6.) Have the students
fill out Part 2 of the student journal activity sheets, which asks
them to rank the concentrations of the solutions from the most concentrated
(darkest color) to the least concentrated (lightest color). Also, have them
qualitatively estimate the concentration of the Unknown
solution by comparing the color of the Unknown
to the colors of A, B
and C and estimate the volume of water
in the Unknown container.
Part 3 Calculating the Actual
Volume of the Unknown
7.) When the students
are finished with Parts 1 and 2, provide them with the number of packets
of KoolAid you added to the Unknown
solution in step 2 and your calculation of the Actual Concentration of the
Unknown. The students will then calculate the Actual Volume of the Unknown.
(i.e. If you added 4 packets
of KoolAid to the Unknown container, then the mass of the indicator
you added would be 4 x 3.4 mg = 13.6 mg. If you calculated the concentration
of the indicator to be 6.8 mg/L, then the students should be able to
divide the mass by the concentration and arrive at the total volume
of the solution. V = M / C = 13.6 mg / 6.8 mg/L = 2 L.)
