Comparing Densities of Different Liquids

Elaine Messal                  Henry Clay Elementary
                               13231 South Burley
                               Chicago IL 60633
                               (312) 535-5600

Objectives:

1) To motivate students to experiment, observe, and calculate densities of 
   several different liquids.
2) To understand that density is the ratio of the mass of a substance to its 
   volume.
3) To be presented with adaptations in grades 4-8.


Materials needed:

 1) Equal quantities of the following liquids:
    Liquid A (water)
    Liquid B (water plus red food coloring)
    Liquid C (water plus blue food coloring)
    Liquid D (dark Karo corn syrup)
    Liquid E (light vegetable oil)
 2) Transparent plastic cups
 3) Graduated cylinders
 4) Balances 
 5) Sets of weights
 6) Small paper cups that fit on the pans of the balance 
 7) Permanent markers
 8) Ice cubes (make them green by adding food coloring)
 9) Additional quart of vegetable oil
10) Paper toweling

Strategy:  

 1) Introduce the lesson by telling a story about Mr. Dense and Miss Smile (a 
    teacher).  Mr. Dense challenged Miss Smile to have one of her students 
    explain and prove to him why his five unnamed liquids reacted in the manner 
    that he described.  The challenge must be met before the end of the week, 
    and the student can't read from a paper.  The student must show and explain 
    why mixing equal volumes of A, B, and E, produced different results than 
    mixing equal volumes of A, D, E, and B, D, E, and C, D, E. 
 2) Place the five bottles of liquids on the table in front of the room as you 
    tell the story. 
 3) Divide the class into teams based on the number of graduated cylinders 
    available. 
 4) Each team should use the graduated cylinder to calibrate two transparent 
    plastic cups into 20ml, 40ml, and 60ml by pouring 20ml of water from the 
    graduated cylinder into each cup and marking it with a permanent marker.  
    Repeat for the 40ml and 60ml calibrations. 
 5) Pour 20ml of liquid A, 20ml of liquid B, and 20ml of liquid C into each 
    calibrated cup. 
 6) Observe, record, and discuss the results, and pour the contents into another 
    unmarked transparent cup. 
 7) Wash out and dry the calibrated cups with paper toweling.
 8) Teams 1 and 2 pour 20ml of A, D, and E into a calibrated cup.
 9) Teams 3 and 4 pour 40ml of B, D, and E into a calibrated cup.
10) Teams 5 and 6 pour 60ml of C, D, and E into a calibrated cup.
11) Discuss and record the results.  After the students explain what happened 
    introduce the definition for density and place it on the board.
12) Place the balances, sets of weights, and paper cups on the table.  Review 
    how to use a balance to obtain the mass of a substance. 
13) Each team should find the masses for the three liquids assigned to them in 
    steps 8-10 and calculate the densities.
14) First they obtain the mass for the paper cup.  Then they obtain the mass for 
    the cup plus the liquid, and subtract the mass of the cup to obtain the mass 
    of the liquid.  Then they use the mass of the liquid and volume to calculate 
    density. 
15) Give each team a chart on which to record their data.  Record the data on 
    the same chart drawn on the board. 
16) Students analyze the data and conclude that D had the greatest density, A, 
    B, and C (all water), were less dense than D, and E was the least dense. 
17) Draw a graph on the board to show the relationships discussed.  Place mass 
    in grams on the vertical axis and volume in ml on the horizontal axis.  
    Title the graph, Mass-Volume Relationship For Different Liquids. 
18) Pour equal volumes of vegetable oil in transparent cups for each group.  
    Place a green ice cube in each cup.  Students observe what happens and 
    explain the results.  The ice cube will float on the top and form drops as 
    it melts and falls down through the vegetable oil. 

Performance Assessment:

 1) Students should be challenged to write how they would prove to Mr. Dense 
    that A, B, and C had the same densities, and the densities of D and E were 
    different.  E was the least dense. 
 2) Students should be given the opportunity to present their explanations to the 
    class.