Question

Density Laboratory: Will choose bes answer

Materials & Apparatus:

Water

Food coloring (red, blue, green)

Salt

4 – 50 mL Erlenmeyer flasks

Transparency (or other stiff flat paper or plastic sheet)

Funnel (optional)

9x13 or 9x9 or 8x8 cake pan

Paper hole punch

Tape (Scotch type)

Duct Tape or clay

Pepper

Procedure:

Effect of temperature on density

Fill two Erlenmeyer flasks with cold tap water and two Erlenmeyer flasks with warm tap water. Add two drops of blue food coloring to the flasks of cold water and 2 drops of red food coloring to the flasks with warm water. Stir the flasks to mix (straw or chop stick should work well). The flasks should be full to the brim.

Place a transparency square over the mouth of one of the warm flasks and carefully invert it over one of the cold flasks. Remove the transparency square from between the flasks. What happens? Record observations.

Repeat the procedure, this time inverting a cold flask over a warm flask. What happens? Record observations.

What is the relationship between temperature and density? How does this explain your observations of the two sets of flasks?

Effect of salinity on density

Rinse the flasks you used above. Add two spoonfuls of salt to two of the flasks and dissolve the salt in tap water (a funnel may be useful here). Fill the flasks to the brim with additional tap water. Place a drop or two of food coloring in each flask so you can distinguish this salt water from fresh water

Fill the remaining two flasks with tap water at the same temperature as the previous two flasks. These flasks contain no salt or food coloring, but like the saltwater flasks should be completely full with water.

Place a transparency square over one of the flasks of fresh water and carefully invert it over a flask of salt water. Remove the square from between the flasksand observe them for a few minutes. What happens? Record observations.

Repeat the procedure, but this time, invert a flask of salt water over a flask of fresh water. Again, remove the transparency square from between the flasks and observe them for a few minutes. What happens? Record observations.

What is the relationship between the salinity of water and its density?

The mystery of the Strait of Gibraltar

The Strait of Gibraltar is an 8-mile wide channel of water that connects the Mediterranean Sea with the Atlantic Ocean. Until the construction of the Suez Canal in 1869, the Strait of Gibraltar was the only connection between the Mediterranean Sea and the Earth’s oceans. See image

Image taken from HYPERLINK "http://www.acklamgrange.org.uk/kensuke/Spain.htm" \t "_top" www.acklamgrange.org.uk/kensuke/Spain.htm

Beginning with Phoenician explorers in approximately 800 BC, many sailors passing through the Strait of Gibraltar into the Mediterranean Sea noticed a strong inward current, with water traveling as fast as two meters per second. When later explorations found no outlet from the Mediterranean, many began to wonder how this sea could continually fill with water without the water level rising. (This is like leaving a bathtub faucet running and finding that the bathtub never overflows.) Some thought an underwater drain was responsible for letting water out of the Mediterranean, whereas others thought the outflow occurred through an undiscovered strait similar to Gibraltar. Neither is true

What explains the mystery of the Strait of Gibraltar?

Develop a hypothesis for this question (before you read through the experiment).

In this activity, you will build a model of the Mediterranean Sea and the Strait of Gibraltar to develop an explanation.

Obtain a cake pan or similar container and an overhead transparency. Cut from the transparency a piece of plastic big enough to serve as a divider across the center of the pan. Using a paper punch, make two holes in the divider, one hole near the top (for surface currents) and one near the bottom (for underwater currents). Temporarily seal each hole with a piece of tape (fold back one end to make a tab). Place the divider in the center of the pan, attaching it to the bottom and sides of the pan with duct tape or clay.

Oceanographers have discovered that the water of the Mediterranean Sea is saltier than the water of the Atlantic Ocean. Make some “sea water” by dissolving two teaspoons of salt per cup of tap water in a container other than your pan (you’ll need about 6-7 cups for a 9x13 pan, 4-5 cups for a 9x9 pan). Add green food coloring to the container to distinguish this salty “Mediterranean” water from the water of the Atlantic Ocean (tap water to which no salt and no food coloring has been added). Your Atlantic Ocean should be the same volume of water as your “Mediterranean” water.

Slowly and simultaneously pour the green salt water into one half of the pan (this is the “Mediterranean” side) and tap water into the other half of the pan (this is the “Atlantic Ocean” side). The water level on both sides should be just high enough to partially cover the top hole in the plastic divider. Sprinkle pepper flakes in the “Atlantic” side of the pan.

Carefully remove the pieces of tape covering the holes in the divider. Observe the movement of food coloring and pepper. Which way does the green salt water move? Which way does the pepper move? Record observations.

Assignment Questions (all work must be shown for all calculations):

Using the results of your lab, complete all the questions below.

Upload one picture representative of your experiment with this report to the appropriate D2L Brightspace Assignments folder.

Answer all the bolded questions throughout the lab.

In part I of this exercise (temperature and density), you may have noticed a purple color develop where the waters mixed. What is the temperature of this water relative to the water in the red and blue flasks?

If you have ever gone swimming in a deep lake you many have noticed the temperature drops off sharply as you go down only 1 or 2 meters. Explain using what you have learned in this experiment.

Plankton are small or microscopic organisms that float in the surface waters of lakes or oceans. Plankton are essential to the survival of all other aquatic life, as they are the base of the food chain. For their growth, plankton depend on nutrients dissolved or suspended in water. Such nutrient-rich water, however, often is denser that other water and therefore sinks to the bottom of lakes and oceans, where it is unavailable to plankton. If the water is undisturbed, the nutrients may remain on the bottom for such a long time that the plankton may die, as well as the other aquatic life that depend on plankton for their survival. Fortunately, changes in water temperature can cause water to mix, bringing the nutrients to the surface. In light of your experiment, explain how this might happen.

An estuary is the region in which the water from a river mixes with the tidal waters of the ocean. Estuaries are very rich ecosystems, supporting a wide variety of plant and animal life. Would you expect halophytic (salt-loving) organisms to live closed to the surface or the bottom of the estuary? In light of your experiment, explain.

In light of your experiment, what is your solution to the mystery of the Strait of Gibraltar? How can water apparently flow into the Mediterranean, but not out?

Hydrometers are used to determine the density of water in car radiators, these tools have lines on them to indicate the density of the liquid they are placed into. Since density varies as a function of the amount of antifreeze (ethylene glycol) added, it is possible to determine the percentage of antifreeze in the radiator and the temperature at which it would freeze. Knowing the density of ethylene glycol to be 0.958 and the density for water is approximately 1.0,would a radiator containing fluid with a density of 0.976 or 0.989 be better prepared for cold weather? Explain.