LSC 254 - Marine Biology
Using the lab manual, Laboratory and Field Guide in Marine Biology, and this handout we will explore
some of the biologically important properties of sea water.
1.
2.
3.
4.
5.
buoyancy
density
sensible heat of water
salinity
osmosis
Density and Salinity and Sea Water
Purpose:
How do the densities of fresh and salt water compare?
How does the addition of salts affect the density of water?
A. Density and Salinity
1) Hydrometer Method
• Use the hydrometer and a graduate or plastic tube to measure the density of the water and
the temperature of the water. Record the results below.
Table 1:
Fresh Water
Sea water
Density
Temperature
Salinity
2) Refractometer Method
• Place a drop of water and read the salinity and density. Measure the temperature of the
water.
Table 2:
Fresh Water
Sea water
Density
Salinity
Temperature
3) Evaporation Method
• Label one 250 ml beaker fresh water and another 250 ml beaker.
• Measure the mass of two 250 ml beakers
• Add 100 ml of fresh water to one beaker and 100 ml of sea water to the other beaker.
• Mass both beakers and water sample.
• Calculate the density of each water sample.
• Place both beakers in the oven to evaporate the liquid.
• Remove beaker from the oven and mass the beaker and residue.
• Calculate the mass of the residue.
• Calculate the salinity.
Table 3:
Fresh Water
Sea Water
Mass of Beaker
Mass of Beaker and Water
Mass of Water sample
Volume of Water Sample
Density of Water Sample
Mass of residue
Salinity of Water Sample
B. Buoyancy
Purpose: How does the buoyancy force of fresh water and salt water on an object placed in the
water compare?
•
•
•
•
Take a 250 ml beaker, a rubber stopper, and a spring balance.
Hang the stopper from the balance and determine the weight if the stopper in air. Record the weight
in air.
Suspend the stopper on the spring balance in the fresh water sample in the beaker, being sure that the
stopper does not touch the bottom or sides of the beaker and that the stopper in completely under
water. Record the weight of the stopper in fresh water.
Repeat the procedure for a room temperature salt water sample and a cold salt water sample.
Table 4:
Object -_________________________________________
Spring Scale
Mass (g)
Mass in Air
temp =
Mass in fresh water
temp =
Mass in sea water
temp =
Mass in cold sea water
temp =
Electronic Balance
Mass (g)
C. LatentHeat of Water
Purpose: Compare the latent heat characteristics of water and air.




Take two black calorimeters sets, two thermometers, and a light source.
Fill one with sea water and the other with air.
Place both equal distances from the light source and record the temperature of each every 5 minutes.
at 30 minutes turn lamp off and continue recording temperature every 5 minutes.
Volume of container = _____________
Table 5:
Time
0
5
10 15 20 25 30 Change
in temp
35
40
45
50
55
60
Change
in temp
Sea water
Air
D. Osmosis
Purpose: Determine the osmotic effect of sea water on cells of living tissue.



Take two petri dish halves.
Put a sea water sample in one and a fresh water sample in the other.
Cut two slices of potato, about the size of a MacDonald's french fry. Pat each slice “dry” with a paper
towel and then mass each slice. Record the mass of each slice.



Place a potato section in each water sample.
After about 15 to 30 minutes pick up each sample and compare how they feel and bend.
Pat each slice “dry” again and mass each sample.
Table 6
Salt Water
Slice mass before
Slice mass after
Change in mass
Fresh Water