by Naomi White, Science Teacher, Jefferson High School, LAUSD
STUDENT HANDOUT Background and Information:
As you might already know, water is chemically H2O--two hydrogen atoms and one oxygen atom. But both our drinkingwater and water in lakes, rivers, oceans, and other bodies of water includeother things than only H2O molecules. Bymeasuring these other components, we can evaluate the water quality. Whentesting fresh water, ecologists usually measure the hardness, and turbidityas well as temperature, water depth and velocity. Salinity, currents, andtides are also important factors in estuarine or ocean waters. Aestheticsand safety factors play an important role in drinking water. With tapwater, important water quality tests may also include iron and heavy metalscontent.To demonstrate that water can contain more than H2O, you will extract the salt from an ocean water sample. Throughcareful measurement, you will be able to calculate the salinity.
Laboratory Procedure:1. Weigh the empty pie pan.
2. Add 100 g to the pan weight and add enough sea water to balance it.
3. Boil the water until it evaporates.
4. Reweigh the pan.
5. Use the data to find the salinity, using the following formula:
weight of salt / weight of salt water x 100 = % salinity
Observations:weight of pan __________
weight of salt water__________
Calculation:1. weight of pan + weight of salt water = weight of pan and water
2. weight of pan and salt - weight of pan = weight of salt
3. weight of salt / weight of water = ratio of salt
4. ratio of salt x 100 = salinity
Discussion Questions:1. What does water contain?
2. Describe two tests of water quality.
3. What is salinity and how did you calculate it?
Los Angeles River Connection is a part of LAEP Learning Exchange.