SLE: ______Name ______# ___
______P-__ Sci – Density Lab: Liquid Rainbow
______Date ______
Group Members:______
8th Grade Lab on Density: Liquid Rainbow
Objective: In this lab, you will explore the properties of density and solubility. You will do this by attempting to layer solutions of different densities on top of one another in order to identify the solutions form densest to least dense.
Materials:
-Graduated cylinders -Food coloring (red, blue, yellow & green) -Plastic Spoons
-Six plastic cups -Disposable pipettes -Test tube rack
-Table Salt -Test tubes -Water
Safety:
-Safety goggles MUST be worn.
-Long hair MUST be secured in a bun prior to entering the science lab.
-Loose clothing such as jackets/hoodies MUST be removed if sleeves will not remain rolled up.
-Salt solutions can irritate hands and eyes. If contact occurs, thoroughly flush the area with water and inform your teacher.
-Handle glassware with care.
Clean-up/Waste Disposal:
-All solutions can be safely washed down the drain.
-Please thoroughly rinse all glassware and the disposable pipettes and plastic cups (we will reuse them).
-Wipe up any spills as soon as they occur. Be mindful not to get food coloring on your clothing!
Procedure: You will be working in groups of 4 or 5. As a group, you will make up 5 salt water solutions of varying densities. Then, your teacher will come by and dye the solutions and mix up their order so that you are left to determine their density rankings: most dense (bottom layer) to least dense (top layer) by attempting to layer the solutions in a test tube to form a “liquid rainbow”.
1. All group members should assist in making the solutions. You will need the following materials to make the solutions:
-6 plastic cups -graduated cylinder
-6 plastic spoons -tap water (room temperature)
-cups of pre-measured salt -beaker (optional)
To make the solutions you will need to use a graduated cylinder to measure out 250 mL of tap water. Be sure to measure the water by properly reading the meniscus of the graduated cylinder. You should use a beaker to help you fill your graduated cylinder. Each solution contains 250 mL of water but varying amounts of table salt (to save time, I have measured out the salt for you and put it in numbered cups that correspond to the solution #). To make the solution, pour the water into a plastic cup, add the salt (if specified) and stir until it dissolves. Solutions may appear cloudy even though all of the salt is dissolved. Typically, we will label the container in which we are making a solution in a secure way to avoid confusion, but in today’s experiment we are going to label the cups with a numbered sticky note because we need the identity of the solution to be a mystery in the next step. The sticky note label will help your teacher to know which solution is which when they come by to dye them. Once they are dyed, the labels will be removed and the solutions will be left in random order. Do not assume all lab groups have the same solution order.
CHART OF SOLUTIONS TO BE PREPARED
SOLUTION # / AMOUNT OF WATER / AMOUNT OF SALT1 / 250 mL / O teaspoons
2 / 250 mL / 1.5 teaspoons
3 / 250 mL / 3 teaspoons
4 / 250 mL / 4.5 teaspoons
5 / 250 mL / 6 teaspoons
Once you have made all of your solutions, please ask your teacher to come by and dye them for you. At this time you will be asked to turn you back so that you do not know which solution is which color.
2. After your solutions have been dyed, you will need the following materials from the side bench:
-test tubes -10 disposable pipettes
-test tube rack -6 additional plastic cups
3. At this point, pour half of each of your solutions in 5 of the 6 additional cups. The 6th cup is for waste. In addition, distribute a clean pipette to each set of 5 solutions. Be sure to avoid cross contamination and use a pipette for a designated solution. You are still working in groups of 4 to get the overall liquid rainbow, but by working in pairs at this point, you will be using your time more efficiently.
4. Begin by observing the 5 solutions, and make a hypothesis about each solution’s relative density. (i.e. Which solution is the densest? Which solution is the least dense?). Then, rank each solution based on its density (1 being the least dense, 5 being the most dense) using the table below.
Color of Solution / Observations / Density Ranking5. Then, using a disposable pipette, suction up the solution you believe to be most dense into the pipette. Remove any air bubbles from the pipette and carefully drip 10 drops of that solution slowly down the side of the test tube. Next, suction up a solution you believe to be less dense (than the one already in the test tube) with a separate pipette and, repeating the technique you just did on the previous solution, attempt to layer this solution on top of the solution already in the test tube. If the solutions appear to be in layers, then you have successfully layered a less dense solution on top of a more dense solution. If the solutions appear to mix, then the second solution you have added may be the more dense solution. Try these solutions again but in the opposite order.
6. Continue to repeat step 5 for sets of two solutions. Make notes along the way as to which solutions you find to be more or less dense. Discuss your findings with your group. The ultimate goal is for your group to show your teacher your “liquid rainbow” consisting of all 5 colors layered in your test tube. Your teacher must initial the box below that they have seen the “liquid rainbow” for your group.
Once you have found the liquid rainbow, label the blocks below as the colors appear in your test tube.
7. After you have completed your experiment, please thoroughly rinse out and dry all of your glassware, cups and pipettes and put them where you are instructed to. Wipe up any spills and make sure your lab bench is clean prior to leaving the lab.
Grading for this experiment:
ALL LAB ASSIGNMENTS MUST BE TYPED. You may download an e-copy of this procedure from my
Edlio page. You can use the e-copy as a template and just fill in the “lines” with your
information/answers. In addition to the question and answer section of the lab write-up, you also
need to type in the data for the tables and charts from within the procedure. Please change your
font and text color (if you have access to a color printer) for your answers so that I can easily
differentiate between my words and yours.
Tip: You may use a “/” to represent division and an “x” to represent multiplication in the
calculation portion of the lab assignment. Be sure to include the units with your answers!
-Unexcused late assignments, turned in within one week of the due date will receive a score
no greater than 50%
-5-10% will be deducted for excessive sloppiness
-5-10% will be deducted for excessive grammar and spelling errors
-ASSIGNMENTS THAT ARE NOT TYPED WILL NOT BE ACCEPTED.
This experiment is worth a total of 41 points:
Performance: 10 pts.
Data Collection: 10 pts.
Questions: 21 pts.
You may need to use your lab preview to help you to answer the questions. If you need help with
your assignment, please ask me for assistance PRIOR to the assignment due date. I am available
most days during recess, lunch, or after school until at least 3:30 PM.
References
“You Be the Chemist” Activity Guide (Teacher resource center www.chemed.org)
SLE: ______Name ______# ___
______P-__ Sci – Density Lab: Liquid Rainbow
______Date ______
Group Members:______
ANALYZE AND CONCLUDE (Please answer all questions in complete sentences.)
1. Did your results correspond to the rankings you listed in your observation chart? Explain. (3 pts.)
______
2. What makes solutions denser than others? (2 pts.)
______
3. Did your data support the Experimental Hypothesis given on your lab preview? Explain. (3 pts.)
______
4. Recall Mrs. Bork’s lesson on precision and accuracy. How could you have improved upon the precision in which each solution was made? (3 pts.)
______
5. In the discussion about solutions on your lab preview, it is said that the volume of the solution remains “relatively” the same as more salt is added to make all 5 of your salt solutions. Why doesn’t the volume remain “exactly” the same as more salt is added?
(2 pts.)
______
6. _ Why do you think the experiment had you use a graduated cylinder instead of a beaker to measure the water for your solutions? (2 pts.)
______
Use the formula for density D = mass/volume (or variations of it, volume=mass/Density, mass = Density x volume) to calculate the following equations. Show your work and remember to include units in your final answer.
7. A piece of wood has a mass of 40 grams and a volume of 8 cm3. What is its density?
(2 pts.)
8. If the density of water is 1 g/mL, what mass does 30 mL of water have? (2 pts.)
9. If the density of gold is 19.3 g/mL, what volume does 10 grams of it take up? (2 pts.)