Full Lab Manual
Introduction & Goals
Chemistry & Background
In Your Write-up
This week you will use an ion exchange column to analyze a sample of natural seawater. Cations in the sample will be exchanged on a column for H+ ions, which combine with water in solution to form H3O+ ions. The acidic effluent solution will then be analyzed by titration with base. You will also determine the concentration of the base solution by standardizing it with a standard acid, potassium hydrogen phthalate (KHP).
To Learn and Review
Titration of a Weak Acid
Zumdahl, pp. 113-117,294-300
Zumdahl, pp. 307-312
Some of the most familiar chemicals are ionic, water soluble salts such as sodium chloride (table salt), potassium nitrate (saltpeter), and magnesium sulfate (Epsom salt). Because of the water solubility and low chemical reactivity of many simple salts, as well as the high terrestrial abundance of their constituent elements, high concentrations of the ions Na+, K+, Ca2+, Mg2+, Cl-, and SO42- have built up in the earth's oceans. They have been leached from mineral deposits by the action of ground water over geological time. Together, these six ions account for 99.6% by weight of the dissolved salt content of the oceans.
It is generally believed that life evolved in the oceans, and living organisms reflect this aquatic past both by a high overall water content (50% for trees, 65% for people, 99.7% for jelly fish) and by an elaborate biochemistry established in salt solutions. These solutions contain the same ions that were brought from the seas by the first amphibians. Thus, perhaps it is not surprising that there is a striking resemblance between the ionic composition of seawater and that of human blood plasma, one of the solvent systems for human metabolic chemistry. More information on the chemical content of seawater is given in the appendix in the lab manual.
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