Potentiometric determination of the potassium in the presence of the ammonium ion with a tetraphenylborate-selective electrode
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DÎRU, Mariana, STÎMKOVSKAIA, Anna, REVENKO, M.. Potentiometric determination of the potassium in the presence of the ammonium ion with a tetraphenylborate-selective electrode. In: The International Conference dedicated to the 55th anniversary from the foundation of the Institute of Chemistry of the Academy of Sciences of Moldova, 28-30 mai 2014, Chișinău. Chișinău, Republica Moldova: Institutul de Chimie al AȘM, 2014, p. 155.
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The International Conference dedicated to the 55th anniversary from the foundation of the Institute of Chemistry of the Academy of Sciences of Moldova 2014
Conferința "The International Conference dedicated to the 55th anniversary from the foundation of the Institute of Chemistry of the Academy of Sciences of Moldova"
Chișinău, Moldova, 28-30 mai 2014

Potentiometric determination of the potassium in the presence of the ammonium ion with a tetraphenylborate-selective electrode


Pag. 155-155

Dîru Mariana, Stîmkovskaia Anna, Revenko M.
 
Moldova State University
 
Disponibil în IBN: 21 iunie 2020


Rezumat

In many real objects along with potassium the ammonium ions are found. If for the
determination of NH4
+ several relatively simple methods are known, then for K+ these possibilities
are less, and those are required more sophisticated equipment and expensive reagents. Using an
sensitive electrode in the presence of tetraphenylborate ions, we developed previously a method
for determination of the potassium content by the rest titration in samples that did not contained
ammonium [1,2].
Taking into account the fact that the tetraphenylborate anion can precipitate the
potassium ions as well as the ammonium ones, forming white substances, which are slightly
soluble and have the solubility product (PS(K[B(C6H5)4] near the value of 3.24.10-8 and
PS(NH4[B(C6H5)4] of 8.41.10-8 [3]), a new method for the determination of the content of
potassium in the presence of the ammonium ion has been developed. So, initially both cations
were precipitated with a known excess of tetraphenylborate by creating the conditions when the
values of the ion product exceed the product of solubility. Later, the excess of tetraphenylborate
has been potentiometrically titrated with a standard solution of potassium chloride using as
indicator the tetraphenylborate-selective electrode [1,2]. Through this operation the equivalent
and summary amount of both cations can be established. The content of ammonium is
determined by acid-base titration and, from the difference, the content of potassium, present in
the sample, can be calculated. A series of model samples with known concentrations of the
potassium and ammonium ions were analyzed.
Table. The results of determination of potassium and ammonium content in model samples

Analyzing the results presented in the table, one may conclude that the values of the
experimentally determined quantities are close to the real ones. This means, that during the
implementation of the experiment we do not commit systematic error. In the samples with an
ammonium content ≤ 10-6 mol, potassium can be only potenţiometrically determined. For these
conditions, the value of the ionic product for ammonium and tetraphenylborate is less than their
solubility product. The presented method is relatively simple, does not require sophisticated
equipment, used reagents being available.
References:
[1] Revenco, M.; Dîru, M.; Stîmcovschi, A. Conf. Ştiin. cu Part. Int.:Interferenţe Universitare–
Integrare prin Cercetare şi Inovare, Rezumatele comunicărilor, 2012, p. 71.
[2] Dîru, M. Autoref. tezei de dr. în ştiinţe chimice, Chişinău, 2012, 28 p.
[3] Kozitskii, V. In: Russian Chemical Bulletin, 1971, vol. 21 (1), 6-9.