The mass law of the reaction also explains this effect where Rconcentration in

The mass law of the reaction also explains this

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The mass law of the reaction also explains this effect: (where R=concentration in the resin surface) H ¿ + ¿ ¿¿ ¿ Cu ¿ 2 + ¿ ¿¿ ¿ ¿ R ¿ H ¿ + ¿ ¿¿ ¿ Cu ¿ 2 + ¿ ¿ ¿ ¿ ¿ ¿ K ' = ¿ Rearranging: 3
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H ¿ + ¿ ¿¿ ¿ ¿ 2 ¿ H ¿ + ¿ ¿¿ ¿ ¿ R ¿ Cu ¿ 2 + ¿ ¿¿ ¿ ¿ R ¿ Cu ¿ 2 + ¿ ¿¿ ¿ ¿ ¿ ¿ ¿ K ' ¿ It can be seen that the ion with the larger K will be stronger retained in the resin. Experiments also show that polyvalent ions have larger Ks than univalent ions. The differences in K in a given charge group also depends on the size of the ions and some of their properties. For the sulfonated cation- exchange resin, like the one used in the experiment, the value of K for divalent cations in decreasing order is: 2 + ¿ 2 + ¿ > Cu ¿ 2 + ¿ > Cd ¿ 2 + ¿ > ¿ ¿ 2 + ¿ > Cd ¿ 2 + ¿ > ¿ ¿ 2 + ¿ > Ca ¿ 2 + ¿ > Sr ¿ 2 + ¿ > Pb ¿ Ba ¿ 4
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Hence, if the unknown sample was contaminated with ions other than Cu 2+ with greater K, most of the Cu 2+ ions will just flow out of the burette until all of the ions with the greater K have reacted with the resin. This trend is often used as an advantage in separating ions in a solution. In addition, if other solvents were added instead of water, the resin might be dissolved at some extent that may affect the resulting H + concentration of the eluent. Also, inadequate regeneration with H + ions may affect the resulting H + concentration measured in titration. With less H + ions, some cations might flow out with the eluent and the resulting concentration will be lesser than the actual cation concentration. An incomplete exchange caused by a faster flow rate or trapped-air pockets will also produce the same results. References: Benjamin, W.A. Quantitative Analysis, 1964 Skoog, et al., Fundamentals of Analytical Chemistry, Eighth edition, 2004 5
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  • Fall '17
  • Sir Jaden Smith
  • Chemistry, Atom, Ion Exchange Chromatography, Electric charge, Ion, Ion Exchange

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