Lesson 1: The Hydrosphere

Wrapping Up


Go back and reread the description in the box on page 109 in Painless Earth Science. Explain to your parent why a pail of saltwater is more dense than a pail of pure water.

Life Application

It is said that conversations must be seasoned with salt so that one is always prepared for an answer in dealing with others. Consider the importance of salt for taste and food preservation. Too much destroys the taste and too little, at one time, led to food spoilage. How salty are your conversations? Not enough, too much, or just the right amount?

Questions to Discuss

  • Give a brief description of density and why it is significant in the hydrosphere. (Answers might include the following: Density is a measure of the mass of a substance to its volume. Density influences how water moves. Denser waters sink and less dense waters rise to the surface causing the movement of both fresh and salt water.)
  • Consider the density of fresh water and salt water. Which one has the greater density? What about warm water or cold water? (Salt water is more dense than fresh water. Cold water is more dense than warm water.)
  • If two liquids are poured into the same container and they do not mix, which one is more dense? (The solution that is less dense will "float" on top of the more dense substance. )
  • In one of the activities, you may have noticed that the saline solutions did not completely freeze. While this result was not discussed, how do you think this would affect the way ocean waters would freeze? (Answers might include the following: Ocean waters freeze at lower temperatures because they contain salt. If the concentration [percentage of salt] in the ocean increased, the freezing temperature of the water would decrease.)
  • Optional: Consider the saline solutions not freezing and briefly explain why salt is used on icy or snow-covered roads. (Salt lowers the freezing temperature of water. As a result, salt added to the roads prevents water from freezing as quickly and can even cause water at freezing temperature to thaw out.)

Things to Review

  • All substances do not have the same density.
  • Density is influenced by what a solution contains. For example, tap water is less dense than salt water.
  • Density plays a significant role in the movement of the oceans' waters.
  • Two factors that influence density are salinity and temperature.