As part of a soil analysis on a plot of land, you want to determine the ammonium

Question

As part of a soil analysis on a plot of land, you want to determine the ammonium content using gravimetric analysis with sodium tetraphenylborate, Na + B(C6H5)4-. Unfortunately, the amount of potassium, which also precipitates with sodium tetraphenylborate, is non-negligible, and must be accounted for in the analysis. Assume that all potassium in the soil is present as K2CO3, and all ammonium is present as NH4CI. A 4.995-g soil sample was dissolved to give 0.500 L of solution. A 150.0-mL aliquot was acidified and excess sodium tetraphenylborate was added to precipitate both K+ and NH4+ ions completely: The resulting precipitate amounted to 0.253 g. A new 300.0-mL aliquot of the original solution was made alkaline and heated to remove all of the NH4+ as NH3.The resulting solution was then acidified and excess sodium tetraphenylborate was added to give 0.119 g of precipitate. Find the mass percentages of NH4CI and K2CO3 in the original solid.

Explanation / Answer

150 mL aliquot contains                            0.2950 g KB(C6H5)4 + NH4B(C6H5)4

150 mL new aliquot contains 0.121/2 g = 0.0605 g KB(C6H5)4 (pay attention here)

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