Name______Period_____ Date______

Water Density and Salinity Lab

Purpose:

To understand how salinity affects the density of water and how pure and salt-water systems work together. To observe how different water densities control the depth at which different water masses occur. (Currents)

Background:

Temperature and salinity affect the density of the water. Ocean salinity differs by small numbers, so oceanographers need to be accurate when measuring salinity. Changes in density caused by wind and currents at the surface affects the deep-ocean currents. Density ultimately affects the objects that are in the water (whales, seaweed, and submarines). The saltier the water, the more buoyant an object becomes. Therefore, salt waters are constantly trying to find their "place" in the ocean according to their salinity. Students should be able to understand that salt or fresh water drops are going to want to "hang out" in water with similar properties. Called stable density distribution. When a different density is added to a solution, then at that moment it is an unstable density distribution. The salinity of the water mixes, or changes, only when vigorously stirred. Though students learn early on that the ocean contains salt water, it still does not mean that all the water has the same amount of dissolved salt. The Navy pays close attention to salinity to be sure they know how the submarines will travel as they move through the different waters of the world.

Objective:

Make a current caused by density using salt and fresh water.

Start: Prediction: When you put salt water with fresh water, what do you think will happen? WHY? (The salt water will…(Explain)______

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Procedure:

Part I

  1. Cup1 (empty– fill ¼ (quarter with yellow fresh water)pipet (slowly on the side of the cup) the green ocean water into the cup
  2. Lean to the side to seeRecord observations (Illustrate). Start (first) contact pipet (initial)Observation AFTER(Illustration)
  1. What happened to the ocean water as you add it to the fresh water? Why?______

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Part II

  1. Cup 2–(empty- fill it ¼ (quarter) full with clear ocean water)
  2. Pipeton the side of the cupyellow fresh water into that cup
  3. As you pipet on the side, observe what happens as the yellowfresh water enters the water in the cup. Pay attention to both the vertical and horizontal movement of the fresh water.
  4. Record observations first contact pipet (initial) Observation AFTER (Illustration)
  1. What happened to the yellow fresh water as it entered the ocean water?Why? ______

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Questions:

  1. Why did the fresh and ocean waternot mix together? ______

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  1. How would an increase in evaporation affect the density of ocean water? ______

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  1. How is density and salinity of ocean water related? ______

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  1. How is this model (lab) of deep ocean currents? ______

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  1. Why is knowing density of an object & currents information important? ______

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  1. Whom would this information be important? Why?______

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  1. Create a symbol that represents the effect of density on ocean water. Explain how the symbol relates to the effect of density on ocean water ______

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  1. Was your hypothesis rejected or supported (Did the water behave as you expected?)Why or why not? How does this model relate to deep ocean currents? ______

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