T11+notes

T11+notes - Exchangeable Cations and Cation Exchange...

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Exchangeable Cations and Cation Exchange Capacity (Topic 11) Cations - ions which have a positive charge - cations are attracted to negatively charged sites Anions - ions which have a negative charge - anions are attracted to positively charged sites How do soil materials develop charge? I. Permanent Charge Isomorphous substitution may result in either positive or negative charge. The substitution of one cation for another within the crystal structure may lead to a charge imbalance. Usually this results in a net negative charge on the mineral. Occurs primarily in layer silicate clays. (Ion charge: Si 4+ , Al 3+ , O 2- ) Tetrahedral sheet Tetrahedral sheet (no substitution) (Al 3+ substituted for Si 4+ ) Si 2 O 4 S i A l O 4 - No charge One excess negative charge II. pH Dependent Charge Mineral edges have broken bonds that can develop a charge Oxides/hydroxides have OH groups on their surface that can develop positive or negative charges depending on the solution pH where M = a metal such as Al
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This note was uploaded on 01/27/2011 for the course SSO 10 taught by Professor Randydahlgren during the Fall '10 term at UC Davis.

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T11+notes - Exchangeable Cations and Cation Exchange...

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