The \"equivalent\" part of ME or meq means that other positively (+) charged ion

Question

The "equivalent" part of ME or meq means that other positively (+) charged ions could be substituted for the Hydrogen. If all of the sites were empty in that 100 grams of soil, and that soil had a CEC of 1, 20 milligrams of Calcium (Ca++), or 12 milligrams of Magnesium (Mg++) or 39 milligrams of Potassium (K+) would fill the same exchange sites as 1 milligram of Hydrogen H+. Why the difference? Why does it take 20 times as much Calcium as Hydrogen, by weight? It's because Calcium has an atomic weight off 40, while Hydrogen, the lightest element, has an atomic weight of 1. One atom of Calcium weighs forty times as much as one atom of Hydrogen Calcium also has a double positive charge, Ca++, Hydrogen a single charge, H+, so each Ca++ ion can fill two exchange sites. It only takes half as many Calcium ions to fill the (-) sites, but Calcium is 40 times as heavy as Hydrogen, so it takes 20 times as much Calcium by weight to neutralize those (-) charges, or 12 times as much Magnesium, atomic weight 24 (Mgt+, also a double charge), or 39 times as much Potassium+. (Potassium's atomic weight is 39, and it has a single positive charge, K+, so it takes 39 times as much K+ as H+ to fill all the exchange sites once again by weight.) The amount of + charges, the quantity of atoms, of K+ or H+, is the same.) 1. What is the atomic mass of Na^+? What is its atomic radius? 2. What is the atomic mass of Mg^2+? What is its atomic radius? 3. What is the atomic mass of Ca^2+? What is its atomic radius? 4. If the CEC of montmorillonite clay is 92.6, how many mg of Na^+ are needed to neutralize all of the negative exchange sites? How many mg Ca^2+? How many Mg^2+? 5. If the degree to which montmorillonite layers swell is related to the atomic radius of the interlayer cations, which cation would lead to the least amount of swelling? The greatest? Explain your answers. 6. Swelling clays are often used to create impermeable barriers as part of landfill liners. When they are fully swelled, water and soluble materials including toxic metal cations, cannot pass through this layer. Based upon your answer to #5 above, which interlayer cation would lead to the most effective barrier? 7. If salt water (NaCl) were introduced to a clay liner, and Na exchanged for other cations in the interlayer, what effect would that have on the swelling capacity? On the effectiveness of the clay as an impermeable barrier?

Explanation / Answer

question no Ions atomic Mass Atomic Radi 1 Na+ 23 102 picometer 2 Mg2+ 24.3 72 picometer 3 Ca2+ 40 100 picometer

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