Groups 1A and 2A: the alkali and alkaline Earth elements – Flashcards
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| base cations |
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| the alkali and alkaline earth metals, more specifically the cations Na+, K+, Mg2+, and Ca2+ |
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| the acidity or alkalinity of base cations |
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| they are actually acid neutral |
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| why the cations Na+, K+, Mg2+, and Ca2+ are called base cations |
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| because they don't hydrolyze to produce protons in the pH 4-9 range of soil solutions |
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| the oxidation state of the alkali metals (group 1A) |
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| +I |
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| the valence of the alkali metals (group 1A) |
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| monovalent |
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| which are stronger bases? group alkali metals or alkaline earth metals? |
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| alkali metals |
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| the oxidation state of the alkaline earth metals (group 2A) |
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| +2 |
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| the valence of the alkaline earth metals (group 2A) |
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| divalent |
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| why the alkali metals are considered strong bases |
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| because their pKa values are >? 14 |
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| why the alkaline earth metals are not considered strong bases |
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| because their pKa values range from 11.44 and 13.47exception: Be2+ |
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| the dominant species in the soil solution |
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| the divalent cations |
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| when the divalent cation is the dominant species in the soil solution |
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| when the soil pH is less than approximately 11 |
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| where the alkali and alkaline earth metals are primarily found |
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| -aluminosilicate minerals -carbonates |
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| how alkali metals are released into the soil solution |
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| thru chemical weathering rxns |
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| how alkali metals exist in soil solution |
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| they exist as free, uncomplexed, soluble monovatemt cations |
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| do alkali metals form soluble complexes with inorganic or organic ligands? |
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| no |
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| the only retention mechanism for alkali metal cations |
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| cation exchange |
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| why cation exchange is the only retention mechanism for alkali metal cations |
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| because they do not form secondary mineral precipitates |
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| one way some cations, such as K+, Cs+, and NH4+ can become unavailable |
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| fixation, in which they become trapped in a clay mineral, such as vermiculite, and become nonexchangeable |
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| what makes Be2+ unique among the alkali earth metals? |
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| it forms neumerous hydrolysis products in pH > 5 solutions and has speciation similar to that of Al3+ |
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| do alkaline earth cations form stable aqueous complexes with inorganic ligands? |
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| yes |
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| some things alkaline earth cations form stable aqueous complexes with in the soil solution |
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| -inorganic ligands -soil organic matter |
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| do alkali earth cations form precipitates in soil? |
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| they can, depending on geochemical conditions |
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| the divalent cations that dominate the cation exchange phase of soils |
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| because they are generally the most abundant cations in soil sollutions |
