Egg Float
A Density Demonstration
SCIENTIFIC
Introduction
This classic and simple demonstration should allow students to start to visualize the difficult concept of density. This demonstration will pique interest and stimulate further activities to explore density.
Concept
•Density
Materials
Graduated cylinders, 500-mL, 3
Funnel, long-stem
Fresh eggs, 3 (medium sized)
funnel
Rubber or latex tubing to fit over the end of the long-stem
Saturated sodium chloride, NaCl, 600 mL
Balance (optional)
Safety Precautions
Although the materials in this demonstration are considered nonhazardous, follow all normal laboratory safety guidelines.
Preparation
1. Prepare a saturated salt solution by slowly adding about 300 g of sodium chloride to 1000 mL of tap water. Stir. If all
the salt does not go into solution, decant the solution.
2. Pour about 400 mL of tap water into the first 500-mL graduated cylinder.
3. Pour about 400 mL of saturated sodium chloride solution into the second 500-mL graduated cylinder.
4. Pour about 200 mL of tap water into the third 500-mL graduated cylinder.
5. Attach rubber or latex tubing to the end of a long-stem funnel so the end of the tubing will reach the bottom of a
500-mL graduated cylinder. Place the funnel into the third cylinder with only 200 mL of water. Make sure the tubing
reaches the bottom of the cylinder.
6. Slowly add 200 mL of saturated sodium chloride solution through the funnel into the third graduated cylinder. Since the
salt water is more dense than the tap water, it will form a layer below the tap water. If the salt water is added slowly, very
little mixing will occur.
7. If necessary, adjust the level of the liquid in all three cylinders to be the same.
Procedure
1. Carefully lower a fresh egg into each of the three 500-mL graduated cylinders. The egg will sink in the tap water, float
in the salt water, and settle at the interface of the salt and tap water layers in the third cylinder.
2. Try to push the egg to the bottom of the salt/tap water cylinder with a meter stick. Does the egg remain on the bottom? Why does it float back up to the middle of the cylinder?
3.(Optional) Mass the three graduated cylinders to demonstrate that each system has a different mass, but all have identical volumes.
Disposal
Please consult your current Flinn Scientific Catalog/Reference Manual for general guidelines and specific procedures governing the disposal of laboratory waste. The salt water may be disposed of according to Flinn Suggested Disposal Method
#26b. Thoroughly wash the eggs after use.
© 2016 Flinn Scientific, Inc. All Rights Reserved.
Publication No. 10507
061616
1
Egg Float continued
Tips
• Different eggs will have different densities depending on shell thickness and the size of the egg. Determine the density of the egg prior to the demonstration. This can be done by massing the egg and determining its volume by volume dis
placement. Most eggs will have a density between 1.06 and 1.09 g/mL.
• The density of saturated sodium chloride is about 1.2 g/mL at 25 °C.
• If fresh eggs are not available, golf balls will also work. Golf balls have a density of about 1.15 g/mL.
• If students have difficulty remembering the density equation, try the following visual aid. Show them a drawing of a heart with a horizontal line through it. Tell them, “Density is mass over volume. If you can’t remember that, it will break my heart.” The line through the heart separates it into an M and a V. Yes, it is a “groaner,” but it works!
=
• Use good quality lab grade sodium chloride or kosher salt. Some lower quality sodium chloride (like rock salt) will give a cloudy solution.
Discussion
Density is a property of material representing the mass per unit volume. It is usually expressed in g/mL, or g/cm3 or g/cc for solids and liquids, and g/L for gases. Specific gravity is the ratio of the density of a substance to the density of a reference material.
For solids and liquids, the reference material is water which has a density of 1.0 g/mL or 1.0 g/cc. Specific gravity is a ratio of
densities, and is therefore a dimensionless quantity—it has no units. Since the volume of many materials change with temperature, the literature values of density and specific gravity are usually reported at a given temperature.
Connecting to the National Standards
This laboratory activity relates to the following National Science Education Standards (1996):
Unifying Concepts and Processes: Grades K–12
Systems, order, and organization
Evidence, models, and explanation
Content Standards: Grades 5–8
Content Standard B: Physical Science, properties and changes of properties in matter, understanding of motions and
forces
Content Standards: Grades 9–12
Content Standard B: Physical Science, structure and properties of matter, motions and forces
Acknowledgment
Special thanks to Kathleen Dombrink from McCluer North High School in Florissant, MO and Jeff Bracken from Westerville
North High School in Westerville, OH for sharing this idea with us.
Materials for Egg Float are available from Flinn Scientific, Inc.
Catalog No.
S0064
GP2030
AP1265
GP5010
Description
Sodium Chloride, Laboratory Grade, 2 kg
Graduated Cylinder, Borosilicate Glass, 500-mL
Graduated Cylinder, Polymethylpentene, 500-mL
Long Stem Funnel, Glass
Consult your Flinn Scientific Catalog/Reference Manual for current prices.
2
© 2016 Flinn Scientific, Inc. All Rights Reserved.