The effective CEC of a soil is measured by 1) saturating the soil with NH4Cl, wh

Question

The effective CEC of a soil is measured by 1) saturating the soil with NH4Cl, which replaces all of the exchangeable cations with NH4+, 2) removing the excess NH4+ by washing (or leaching the soil), 3) displacing the NH4+ in exchange sites by adding 1 M KCl, and 4) measuring the concentration of NH4+ in the KCl extract. Calculate the CEC of a soil in which the NH4+ in exchangeable sites was displaced by shaking 20 g of soil with 200 mL of 1 M KCl solution. The concentration of NH4+ in the extracted solution was 150 mg NH4+/L.Express the CEC in meq/100 g of soil (Review page 30, textbook).

Explanation / Answer

weight of the soil = 20 g

concentration of NH4+ ion in the extracted solution = 150mg NH4+/L

volume of solution = 200ml

total mass of NH4+ ion in the soil = 150 mg/L * 0.2 L

= 30 mg

so 30 mg of NH4+ is present in 20 g of soil

amount of NH4+ that will be present in the 100 g of soil = 150 mg

moles of NH4+ in 100 g of soil = 150mg/ mass of NH4+

= 150mg/18

= 8.33 milli moles

CEC of soil= 8.33 meq/100g

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