Mass, Fluid Volumes, and Concentrations
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 Kool-Aid 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 teacherís 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:
Materials for each group:
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 2-4 Kool-Aid 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 Kool-Aid in containers A, B and C and mix thoroughly so that no Kool-Aid 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 Concentration6.) 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 Unknown7.) When the students are finished with Parts 1 and 2, provide them with the number of packets of Kool-Aid 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.