Oceanography

Colligative and Other properties of sea water

Colligative properties

Colligative properties are those properties of solutions that depend on the number of dissolved particles in solution, but not on the densities of the solutes. For example, the freezing point of salt water is lower than that of pure water, due to the presence of the salt dissolved in the water. To a good approximation, it does not matter whether the salt dissolved in water is sodium chloride or potassium nitrate; if the molar amounts of solute are the same and the number of ions are the same, the freezing points will be the same. For example, AlCI₃ and K₃PO₄ would exhibit essentially the same colligative properties, since each compound dissolved to produce four ions per formula unit. The four commonly studied colligative properties are a)freezing point depression,b) boiling point elevation, c)vapor pressure lowering, and d)osmotic pressure.. Since these properties yield information on the number of solute particles in solution, one can use them to obtain the molecular weight of the solute.

Colligative Properties of Seawater:

The dissolved salts in seawater accounts for some of the properties of seawater that distinguishes it from freshwater:

· Salts lower the freezing point of seawater from 0⁰C -2⁰C.

· Salt increases the boiling point of seawater and seawater evaporates more slowly.

· The heat capacity of seawater decreases with increasing salt content.

· Osmotic pressure increases with increasing salt content.

· The greater the salinity, the greater the electrical conductivity of water.