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Further Investigations: Measuring Salinity

  1. Other methods for determining the salinity of a water sample are described below. Obtain more information about these methods or try the methods yourself.
    1. Recover the salts from a sample of seawater by evaporating all the water from a 1,000 g sample of seawater, then weighing the solid salts that remain. The salinity of the seawater sample can then be calculated using the formula given at the beginning of this topic.
    2. Measure the electric current that flows between two electrodes immersed in a solution. The conductivity of a salt solution is directly related to the salinity.
    3. Measure the angle at which light is refracted or bent by a solution using a refractometer. A refractometer measures the amount of light that is refracted by a solution. Solutions of greater salinity refract more light.
       
  2. Using the procedure in the activity, construct a hydrometer and a density graph to be used for solutions at other temperatures. For example, cool the solutions to 10˚C and repeat the procedures.
     
  3. Using your hydrometer, determine the salinity of samples of different types of water, such as tap water, rainwater, water from a stream or lake, an estuary, the seashore, the open ocean, and freshwater or seawater aquaria.

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Exploring Our Fluid Earth, a product of the Curriculum Research & Development Group (CRDG), College of Education. University of Hawaii, 2011. This document may be freely reproduced and distributed for non-profit educational purposes.