Effect of Temperature on Density One of the most important, and easily measured

Question

Effect of Temperature on Density

One of the most important, and easily measured variables that affect the density of seawater is temperature.

The purpose of this experiment is to determine whether cold water or warm water has the greater density (is ‘heavier’). This is accomplished by pouring warm water into a tube of cold water, and then repeating the experiment by pouring cold water into a tube of warm water, and comparing the results. Provide photos of your experiments.

Part 1

Fill a graduated cylinder with cold water to the 100ml line.

Fill a test tube with about one inch of hot water, and add one drop of food coloring.

Tip your cylinder slightly so you can carefully and gently pour the hot water into the graduated cylinder containing the cold water.

You, or your lab partner should photograph the experiment when the water is being poured.

Describe what happens when the two different water masses are combined.

Does the hot water sink or float?

Part 2

Fill a graduated cylinder with hot water to the 100ml line.

Fill a test tube with about one inch of cold water, and add one drop of food coloring.

Carefully and gently pour the cold water into the graduated cylinder containing the hot water.

You, or your lab partner should photograph the experiment when the water is being poured.

Describe what happens when the two different water masses are combined.

Does the cold water sink or float?

Compare the results of your two experiments.

Where on Earth do you think that water will sink (have high density)? Where will it have low density?

Would you expect the density contrast to increase or decrease as the difference in temperature between warm and cold water masses increases? How could you test this?

Effect of Salinity on Density

Salinity, the salt content of water, is another variable which affects the density of water. This experiment is similar to the previous one, except that you will add salty (saline) water to non-saline water, and compare the density of the two. Provide photos of your experiments.

Part 3

Pour 100 ml water into a cup or test tube.

Add 1/4 tsp (1.5g) of salt and 1-2 drops of food coloring to the 100 ml of water.

Pour about an inch of this saline solution into a test tube or cup, and set the rest aside for later in the experiment.

Fill a graduated cylinder to the 100ml mark with plain, tap water.

Carefully and gently pour the saline solution from the test tube into the cylinder of plain tap water. Start the stopwatch as one member of the group starts to pour. Stop the stopwatch when the colored, saline solution first reaches the bottom of the cylinder.

Empty the graduated cylinder, refill it with fresh water, and repeat the experiment.

Describe what happened when you added the saline solution to the tap water.

How long did it take for the saline solution to first reach the bottom of the cylinder?

What is the density of the saline solution you added? (remember water weighs 1gram per ml, and you added 1.5grams of salt; you can ignore the added volume of the salt)

If you changed the salinity of your solution, how would it affect the speed at which the saline solution sinks?

What environmental factors might affect the salinity of waters in the ocean?

Why is salinity often low in the tropics near the equator?

Why is salinity often high in the mid-latitudes?

Why is salinity often high near the poles?

Since polar regions have both high salinity and low temperature, what do you predict is their influence on global deep ocean currents?

Explanation / Answer

Answer- By the experiment it is shown that higher the temperature less be water density and lower the temperature the denser will be the water. So the cold water is more denser than warm water. In the experiment when we pour the warm water over the cold water. and mixing of warm and cold water result in the layer of warm water over cold water. cold layer occur at the bottom of the cylinder and warm water occur at the top of the cylinder.

On Earth at the pole cold water sink. at the poles (North and south poler) water temperature is too low so water is very dense in nature. At the equatorial and subtropical ocean which is characterize by high temperature throughout year.At such place water is warm so water is of low density.

If the contrast of colder and warmer mass increase results in larger the differences between the density of water masses. larger the temperature contrast increase will be density difference between water column.

the salinity of ocean water in ocean is goverened by the following environmental factor

- ocean temperature- higher temperature high salinity and low temperature low salinity

- ocean pressure

-latitude- salinity is high at subtropical and eqautorial region and low in polar regions

- chemical dissolution of mineral and gases.

- precipitation and evaporation- if evaporation is higher, higher will be salinity of ocean water. and it precipitation is higher than evaporation it will result in less salinity

- freezing and melting- freezing of ocean water increase the salinity and melting of ocean water by the input of freshwater in the form of precipitation decrease the salinity

salinity is low near the equator because equatorial region recieve high ocean temperature but also heavy precipitation thoughout the year. precipitation is greater than evaporation that result in low salinity ocean water

at the mid latitude region. temperature is also high and also there is no input of river runofff in the ocean thatsy ocean salinity is higher. if there would be river runoff input then ocean salinity will be lower

at the poles the ocean water temperature is very low and water is denser in nature. we also know that colder water rich in mineral abundence hence the salinity of polar region high.

In the polar region low temperature and high salinity result in generation of deep ocean current these current are density driven. they move from higher density region (polar region) towards low density region (equatorial region). when these current move towards warm ocean the upwelling occurs and when it move over cold ocean water downwelling of these deep ocean current occurs.

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