How Slaty Does the Sea Have to Be for an Egg to Float?

How slaty does the sea have to be for an egg to float?

Abstract

Some objects float on top of the ocean, and other objects sink to the bottom. Why? Try this eggsperiment to find out!

Objective

The goal of this science fair project is to determine what salt concentration will float an egg.

Introduction

Did you know that if you put an egg in a cup of tap water, it will sink to the bottom? But, if you add enough salt, the egg will float back up to the surface! Why? Because the density of the egg is higher than the density of tap water, so it sinks. Density (ρ), as shown below in Equation 1, is the mass (m) of a material per unit volume (v). For example, the density of freshwater under standard conditions is approximately 1 gram (g) per cubic centimeter (cm3). In other words, if you filled a 1-cm x 1-cm x 1-cm box with freshwater, the water inside the box would have a mass of 1 g. Adding salt to the water increases the density of the water, because the salt increases the mass without changing the volume very much. With enough added salt, the saltwater solution density is higher than the egg's, and the egg will then float.

But just how much salt is needed to make an egg float? In this science fair project, you will figure that out by using the technique of making serial dilutions. A serial dilution is a method for accurately diluting a solution in regular steps. You add a known amount of your starting, or stock, solution to a known amount of water and mix them. The new concentration will be determined by the ratio of the volume of stock solution to the total volume, as shown in Equation 2.

If the volume of stock solution and the volume of water are equal, you'll be diluting the solution by half. This is called a two-fold dilution. If you want bigger steps, you should use relatively more water; if you want smaller steps, you should use relatively less water. By repeating the process, you can make a whole series of dilutions, which is how the method got its name. In this science fair project, you will start out using two-fold dilutions to find out how much salt will cause an egg to float.

Terms, Concepts and Questions to Start Background Research

To do this science fair project, you should do research that enables you to understand the following terms and concepts:

* Density

* Mass

* Volume

* Serial dilution

* Stock

* Concentration

* Relative concentration

* Absolute concentration

Materials and Equipment

* Bag of clear 16-oz. plastic cups

* Table salt

* Water

* Measuring cup, liquid

* Container, 1-quart (qt.)

* Spoon for stirring

* Spoon for egg transfer

* Eggs (5)

* Lab notebook

Experimental Procedure

1. Take one