In this lab exercise a solution containing K + is passed down an ion exchange co

Question

In this lab exercise a solution containing K+ is passed down an ion exchange column containing a cation exchange resin in the acid form. The K+ ions in the solution replace the resin bound H3O+ ions which elute from the column and then are titrated. This means that the column now holds the K+ ions. To use the column again we must "recharge" the column to remove K+ ions. In your Lab Notebook, describe the exact procedure you will follow to "recharge" the exchange column for the next use.

A 0.167 gram solution of KxFe(C2O4)yzH2O is dissolved in water and the solution is passed down a column containing a cation exchange resin in the acid form. The eluted solution is then titrated with a standard NaOH solution to the first equivalence point. Experimentally it required 10.49 mL of a 0.182 M NaOH solution to reach the first equivalence point.

Calculate the number of moles of K+ in the weighted sample.

Calculate the mass (grams) of K+ in the weighted sample.

Calculate percent of potassium in the weighted sample.

Explanation / Answer

Volume = 10.49 mL =0.01049 L

Moles of NaOH = molarity x volume = moles of K+

= 0.182 moles/L x 0.01049

= 0.00190918 moles

Mass of K+ = moles x molecular weight

= 0.00190918 moles x 39.1 g/mol

= 0.074648938 g

percent of potassium in the weighted sample

= 0.074648938 g x 100 / 0.167 g

= 44.69%

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