Chemlab: Chemistry 3/5


Natural Salt Solutions 1: Ion Exchange

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Image 1 Goals
In this two-week experiment, you will learn how to use an ion-exchange column and how to carry out an acid-base titration using an indicator. You will then apply these skills to determine the total concentration of cations in a sample of seawater. This week you will concentrate on understanding the chemistry of ion exchange and estimate the capacity of an ion exchange column from your observations.

To Learn or Review
Ion Exchange Resins
Zumdahl, pp. 859-860

Acid-Base Reactions
Zumdahl, pp. 112-113

Acid Strength
Zumdahl, pp. 227-229

pH
Zumdahl, pp. 231-232

Introduction
An ion exchanger is a porous insoluble material, which contains loosely bound ions. These may be positively charged (cations), or negatively charged (anions). These ions are readily exchanged for the ions in a salt solution, which is in contact with the ion exchanger. Many natural clays and minerals have these properties, and they play important roles in the chemistry of soils and natural water sources.

The ion-exchange resins used in this lab are synthetic polymers. They are very large molecules constructed by linking together many identical or very similar basic structural units. Polymers can be natural or synthetic and include such diverse compounds as proteins, nucleic acids, nylon, and teflon. Typical proteins have molecular weights ranging from 6,000 to 600,000 and can contain thousands of atoms. The synthetic ion exchangers used in this experiment consist of linear chains with molecular weights of a few hundred thousand. Furthermore, the chains are connected by a system of crosslinking bonds. The resulting network is a three dimensional skeleton of carbon-carbon bonds. For more information about the chemistry of the ion exchangers you will use this week, see the Chemistry page.
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