Determination of the acidity constant of isothiocyanic acid in aqueous solution

2000 ◽  
Vol 78 (12) ◽  
pp. 1627-1628 ◽  
Author(s):  
Y Chiang ◽  
A J Kresge
Keyword(s):  
Aqueous Solution ◽  
Acid Solution ◽  
Acidity Constant ◽  
Acidity Function ◽  
Acid Base ◽  
Perchloric Acid Solution ◽  
Thiocyanate Ion ◽  
Acid Base Titration ◽  
Aqueous Perchloric Acid

Changes in absorbance of the thiocyanate ion (SCN–) at λ = 220 nm, measured in concentrated aqueous perchloric acid solution, were analyzed using a titration curve expression containing the Xo excess acidity function; this provided the acidity constant Ka = 19.2 ± 1.1 M, pKa = –1.28 ± 0.03, for isothiocyanic acid (SCNH).Key words: isothiocyanic acid (acidity of), thiocyanate ion (basicity of), acid–base titration in concentrated aqueous acids, Xo excess acidity function, Cox–Yates method.

scholarly journals USING POTENTIOMETRIC ACID-BASE TITRATION TO DETERMINE PKA FROM MANGOSTEEN PERICARPS EXTRACT

2019 ◽  
Vol 16 (32) ◽  
pp. 768-773
Author(s):  
L. TANIA ◽  
C. DIAWATI ◽  
M. SETYARINI ◽  
N. KADARITNA ◽  
A. SAPUTRA
Keyword(s):  
Oxalic Acid ◽  
Potentiometric Titration ◽  
Accurate Determination ◽  
Acidity Constant ◽  
Equivalence Point ◽  
Acid Base ◽  
Titrant Volume ◽  
Acid Base Titration ◽  
Ph Range

One of the uses of acid-base indicators is to show the end point of the titration, so the accurate determination of acidity constant and pH range of indicators needs to be done. This study aims to determine the acidity constant (pKa) of mangosteen pericarp extract and its accuracy as an indicator of acid-base titration. Determination of pKa was done by a simple potentiometric titration method. The titration data were plotted in three graphs, i.e., pH, ΔpH/ΔV (the (the first derivative), and Δ2pH/ΔV2 (the second derivative) versus titrant volume to determine the equivalence point of the titration. The accuracy test was carried out by comparing the volume of oxalic acid used to titrate NaOH solution using the indicator of mangosteen pericarp extract and phenolphthalein indicator. The result showed that the equivalence point was found on the titrant volume of 8.6 mL and a measured pH of 9.84. so the pKa value of mangosteen pericarp extract was 7.20, and the pH range was 6.20 to 8.20. the average volume of oxalic acid used to titrate 5 mL of NaOH using phenolphthalein as the indicator was 5.2 mL while the titration used mangosteen pericarp extract was 5.23 mL. The accuracy of mangosteen pericarp extract was 99.42%. By the result, it can be concluded that potentiometric titration can be used as a simple way to determine the acidity constant of mangosteen pericarp extract. Moreover, the mangosteen pericarp extract can be used as an alternative acid-base titration indicator to substitute the common acid-base titration in the laboratory.

Carbon protonation of some phenylynamines in concentrated aqueous perchloric acid solution. Lowering of the upper limit for the pKa of phenylynammonium ions

1996 ◽  
Vol 74 (7) ◽  
pp. 1373-1376 ◽  
Author(s):  
A.J. Kresge ◽  
S.W. Paine
Keyword(s):  
Acid Solution ◽  
Perchloric Acid ◽  
Rate Theory ◽  
Acidity Function ◽  
Perchloric Acid Solution ◽  
Hydronium Ion ◽  
Dilute Acid Solution ◽  
Saturated Compound ◽  
Initial States ◽  
Aqueous Perchloric Acid

Rates of carbon protonation of five phenylynamines (PhC≡CNH2, PhC≡CNHiPr, PhC=CNHC6F5, PhC≡CN(CH2CH2CN)2, and PhC≡CNMeC6F5) were determined in concentrated aqueous perchloric acid solution and the data were analyzed by the Cox–Yates method using the X0 acidity function. The extrapolated hydronium-ion catalytic coefficients so obtained are consistent with values measured directly in dilute acid solution, and the slopes of the Cox-Yates plots are similar to predictions made with the aid of Marcus rate theory for reactions originating from free ynamine initial states but unlike those predicted for reactions starting from nitrogen-protonated ynammonium ion initial states. This shows that none of these phenylynamines are protonated in even the most acidic solutions used (4 M) and sets new upper limits as low as pKa ≤ −3.1 for the conjugate acids of these ynamines. Comparison of the pKa limit for PhC≡CNH3+ with a literature value for the corresponding saturated compound, PhCH2CH2NH3+, gives a base-weakening effect for the phenylethynyl group of at least 12.5 pK units. Key words: acetylenic amines, concentrated acids, X0 excess acidity scale, Cox-Yates method, Marcus rate theory.

Kinetics and mechanism of oxidation of DL-α-alanine by permanganate ion in acid perchlorate media

1991 ◽  
Vol 69 (12) ◽  
pp. 2018-2023 ◽  
Author(s):  
Refat M. Hassan
Keyword(s):  
Amino Acids ◽  
Ionic Strength ◽  
Acid Solution ◽  
Second Order ◽  
Perchloric Acid Solution ◽  
Oxidation Reduction ◽  
Initial Stage ◽  
Aqueous Perchloric Acid ◽  
Mechanism Of Oxidation ◽  
Kinetics Of

The kinetics of permanganate oxidation of DL-α-alanine in aqueous perchloric acid solution at a constant ionic strength of 2.0 mol dm−3 has been investigated spectrophotometrically. The reaction was found to show second-order kinetics overall with respect to each of the reactants in the slow initial stage; the second-order kinetics are not, however, maintained throughout the relatively fast final stage of reaction. The added salts lead to the prediction that Mn(III) and (or) Mn(IV) play a very important role in the reaction kinetics. A tentative mechanism consistent with the kinetics is discussed. Key words: kinetics, oxidation, reduction, amino acids, permanganate.

Dinuclear complexes of tetravalent cerium in an aqueous perchloric acid solution

2012 ◽  
Vol 41 (24) ◽  
pp. 7190 ◽  
Author(s):  
Atsushi Ikeda-Ohno ◽  
Satoru Tsushima ◽  
Christoph Hennig ◽  
Tsuyoshi Yaita ◽  
Gert Bernhard
Keyword(s):  
Acid Solution ◽  
Perchloric Acid ◽  
Dinuclear Complexes ◽  
Perchloric Acid Solution ◽  
Aqueous Perchloric Acid ◽  
Tetravalent Cerium
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