Titration of cyanide and hexacyanoferrate(II) with silver nitrate-II Determination of sodium cyanide and sodium hexacyanoferrate(II) in a complexing agent

Cyanide and hexacyanoferrate(II) can be titrated with silver nitrate in the presence of a complexing agent masked with a suitable metal ion. A method for determination of sodium cyanide and sodium hexacyanoferrate(II) in the presence of sodium nitrilotriacetate masked with magnesium ions is given as an example.     

Solid-state ion-selective electrodes for the potentiometric determination of hexacyanoferrate (II)

Hexacyanoferrate(II)-sensing electrodes were prepared by mixing Ag₂S and Ag₄Fe (CN)₆. The 6:1 Ag₂S/Ag₄Fe (CN)₆ provided the best potentiometric response and speed of response. The log concentration vs. potential curves were linear with Nernstian slope (14.8 mV/decade) over the range 10^?1-10^?6 M hexacyanoferrate (II) at pH 7.00 with constant ionic strength. Interferences included iodide, sulfide and bromide. This electrode was used as indicator in potentiometric titrations of hexacyanoferrate (II).     

The potentiometric titration of mercury(II) with cetylpyridinium chloride

Summary New precipitation titrations have been evaluated for the determination of mercury(II) in acid solution and for mercuric cyanide solutions. In acid or neutral solutions the mercuric ion was converted to the bromo complex by addition of excess potassium bromide. Mercuric cyanide was converted to the tetracyano complex by addition of an excess of potassium cyanide. In both cases the complex anions were titrated potentiometrically vs. 0.01M cetyl-pyridinium chloride. Emf's were monitored with a home-made graphite sensor coated with a solution containing poly(vinyl chloride) and dioctylphthalate in tetrahydrofuran and a single-junction reference electrode.

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Über die potentiometrische Titration von Hg(II) mit Cetylpyridiniumchlorid

Zusammenfassung Neue Verfahren zur Fällungstitration von Hg(II) in saurer Lösung sowie von Lösungen von Quecksilbercyanid wurden angegeben. Quecksilberion wird in saurer oder neutraler Lösung durch Zusatz überschüssigen Kalium-bromids in den Brom-Komplex übergeführt. Quecksilbercyanid wird durch Zusatz überschüssigen Kaliumcyanids in den Tetracyanokomplex umgesetzt. In beiden Fällen werden die komplexen Anionen potentiometrisch gegen 0,01M Cetylpyridinium-chlorid titriert. Die EMK wird mit Hilfe eines selbst hergestellten Graphitsensors, der mit einer Lösung von Polyvinylchlorid und Dioctylphthalat in Tetrahydrofuran überzogen ist, sowie einer Single-junction-Bezugselektrode gemessen.

     

Kinetics and mechanism of mercury(II)-catalysed replacement of cyanide in hexacyanoferrate(II) by p-nitrosodiphenylamine

The mercury(II)-catalysed replacement of cyanide in hexacyanoferrate(II) by p-nitrosodiphenylamine (p-NDA) in aqueous solution has been investigated spectrophotometrically by measuring the change in absorbance of the green complex ion, [Fe(CN)(5).p-NDA](3-), at 640 nm. Activation parameters of the catalysed and uncatalysed reactions have been calculated. The effects of the dielectric constant and water content of the medium on reaction rates are used to explain the formation of a polar activated complex and suggest an I(d) mechanism for the catalysed reaction. The varying catalytic activity of Hg(II) as a function of concentration has been discussed.     

The silver(I)‐catalyzed exchange of coordinated cyanide in hexacyanoferrate(II) by phenylhydrazine in aqueous medium

The [Ag]⁺‐catalyzed exchange of coordinated cyanide in [Fe(CN)₆]^4? by phenylhydrazine (PhNHNH₂) has been studied spectrophotometrically at 488 nm by monitoring increase in the absorbance for the formation of cherry red colored complex [Fe(CN)₅PhNHNH₂]^3?. The other reaction conditions were pH 2.80±,0.02, temperature = 30.0 ± 0.1^°C, and ionic strength (I) = 0.02 M (KNO₃). The reaction was followed as a function of pH, ionic strength, temperature, [Fe(CN)^4?₆], [PhNHNH₂], [Ag⁺] by varying one variable at a time. The initial rates were evaluated for each variation using the plane mirror method. The initial rates evaluated as a function of [Fe(CN)^4?₆] clearly indicate that the initial rate increases with the increase in [Fe(CN)^4?₆] and finally reaches to a limiting value when [Fe(CN)^4?₆]/[AgNO₃] ? 1000. It indicates the formation of a strong adduct between [Fe(CN)₆]^4? and AgNO₃ prior to the abstraction of CN^?. The variation in initial rates with [PhNHNH₂] also showed limiting values at [Fe(CN)^4?₆]/[PhNHNH₂] ? 8.30. The complex behavior due to pH and [Ag⁺] variations on the rate has been explained in detail. The composition of the final reaction product [Fe(CN)₅PhNHNH₂] formed during the course of reaction has been found to be 1:1 using the mole ratio method. The evaluated values of activation parameters for the catalyzed reaction are E_a = 53.85 kJ mol^?1, Δ H^≠, = 51.33 kJ mol^?1, and Δ S^≠ = ?134.63 J K^?1 mol^?1, which suggest an interchange dissociative mechanism. A most plausible mechanistic scheme has been proposed based on the experimental observations. © 2007 Wiley Periodicals, Inc. Int J Chem Kinet 39: 447–456, 2007     

Determination of equivalence points of sigmoidal potentiometric titration curves

The equivalence point of potentiometric titration curves coinciding with the point of inflection is calculated from the maximum of the first derivative or the zero of the second derivative. The approximation of the curve is carried out by means of cubicB-splines. The quality of the fitted curve depends on the number and position (proportionally spaced or equidistant) of knots. Series of simulated and measured titration curves were evaluated. Optimum fits were obtained with knot numbers about 20–35% of the number of data points. Only proportionally spaced splines are applicable for all types of curves and produce results of high accuracy.     

Theory of titration curves : Points of minimum slope on potentiometric strong acid-strong base and precipitation titration curves

Strong acid-strong base and precipitation titration curves, like other kinds of potentiometric titration curves, inherently possess an inflection point where the slope is a minimum as well as one where it is a maximum. In any kind of titration the first of the inflection points can be caused to occur earlier, and can eventually be made to disappear altogether, by adopting certain expedients. For a weak acid-strong base titration, for example, these include decreasing the concentration of the acid titrated and titrating in the presence of an excess of its conjugate base. For strong acid-strong base and precipitation titrations they include decreasing the concentration of the substance titrated and increasing the concentration of the titrant. The conditions under which a physically significant inflection point of minimum slope can exist are defined, and explicit equations are given from which its position can be calculated under various experimental conditions, for strong acid-strong base and for both isovalent and heterovalent precipitation titrations.     

A silver electrode in the potentiometric titration of thiols

A silver wire immersed in a thiol solution gives a potential responsive to the thiol concentration, and is a sensitive indicator electrode in the potentiometric titration of thiols with mercury(II) chloride, p-chloromercuryphenyl sulphonate, and silver nitrate at pH 4.5-9.5, 7-9.5 and 9.5 respectively. Titrations of simple thiols such as cysteine or a protein such as albumin are equally successful, but the potential break was smaller for the protein. The end-point could be determined within an increment of titrant equal to 5 nmole of thiol. An inert atmosphere is needed for titration at pH 7.     

The potentiometric titration of iron(II)/HCl solutions with permanganate

Summary Reagents other than the Zimmerman-Reinhardt reagent have been used to minimize the errors incurred when Fe(II)/HCl systems are titrated with MnO₄ ^–. Potentiometric studies made of the effect of these additives on the initial and equivalence point potentials show that salts whose anions stabilize the Mn(III) state affect the equivalence point potential more than those containing Mn(II). The cation also affects the result, e.g., H₂SO₄ ^– and Na₂SO₄-containing solutions show a greater equivalence potential change than do those containing (NH₄)₂SO₄ and K₂SO₄. Ce₂(SO₄)₃, reportedly an effective inhibitor, does not affect the equivalence point potential. Less titrant is required for 6 M HCl-containing Fe(II) solutions than for 1 M HCl-containing solutions-a result opposite to that expected and only partially explained by a more rapid air-oxidation of Fe(II) in 6 M HCl. The Pt electrode is not inert in this system.

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Zusammenfassung Bei einer Untersuchung der potentiometrischen Titration salzsaurer Eisen(II)-lösungen mit Permanganat wurde die Wirkung der verschiedenen für diese Bestimmung zur Verhinderung von Störungen empfohlenen ZusÄtze geprüft. Dabei ergab sich, da\ Salze, deren Anionen das dreiwertige Mangan stabilisieren, das Potential im Äquivalenzpunkt stÄrker beinflussen als solche, die zweiwertiges Mangan enthalten. Da\ auch das Kation das Ergebnis beeinflu\t ergab sich daraus, da\ bei H₂SO₄ und Na₂SO₄ eine grö\ere PotentialÄnderung im Äquivalenzpunkt beobachtet wurde als bei (NH₄)₂SO₄ und K₂SO₄. Bei Ce₂(SO₄)₃ wurde keine Wirkung auf die PotentialÄnderung festgestellt. Für 6 M salzsaure Fe(II)-Lösungen wurde weniger Titrationsmittel verbraucht als für 1 M salzsaure, was nur zum Teil mit der schnelleren Luftoxydation des zweiwertigen Eisens im 6 M HCl-Lösung erklÄrt werden kann. Die Platinelektrode erwies sich in diesem System nicht als inert.

     

A potentiometric detector for hydrogen cyanide gas using silver dicyano complex

A sensitive method capable of detecting Hydrogen cyanide gas in atmosphere at its TLV is being presented. This method makes use of two silver electrodes kept in two separate compartments which are in contact with a solution of constant concentration of Silver dicyano complex at a pH 11.5. One of the electrodes used as reference is concealed and the other used for sensing is exposed to the incoming air. In the absence of Hydrogen cyanide gas the potential difference between the two electrodes is zero, but when hydrogen cyanide gas is passed into the cell, the activity of Ag(+) ions nearer to the sensing electrode changes, there by generating a potential difference between the two electrodes. The plot between the potential vs. log of Concentration of Hydrogen cyanide gas is linear, in the concentration range 0.66-42.3 mg/m(3) with a slope nearer to 120mV and regression coefficient around 0.997. The standard deviation is 6% (n=4). Minimum detectable limit is 0.66 mg/m(3). Various concentrations of Silver dicyano complex used gave similar plots.     

A graphical method for locating the end point in potentiometric titration curves

Summary A new graphical method for locating the end point in potentiometric titration curves is described. By moving two glass rods to scan the entire curve, the end point is determined when the difference between the two refracted lines is maximum. The method is particularly useful when the end point is ill-defined.

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Graphisches Verjahren zur Bestimmung des Endpunktes potentiometrischer Titrationskurven

Zusammenfassung Zwei gleich starke Glasstäbe werden senkrecht zur Volumenachse über die Titrationskurve geführt. Der Endpunkt ist durch den maximalen Abstand der durch die Refraktion verzerrten Titrationskurve gekennzeichnet. Das Verfahren eignet sich auch noch bei Titrationskurven mit sonst schlecht definiertem Endpunkt.

     

Natural pyrite as an electrochemical sensor for potentiometric titrations with EDTA, mercury(II) and silver(I)

The results obtained in potentiometric titrations of copper(II), mercury(II) and iron(III) with standard EDTA solutions are presented. The titration of copper(II) at pH values in the range from 8.11 to 10.99 (ammonia buffer) and the titration of mercury(II) and iron(III) at pH values from 3.59 to 5.65 (acetate buffer) were performed. The titration end-point (TEP) was detected with an indicator electrode made from natural crystalline pyrite as an electrochemical sensor. The results obtained in potentiometric titration with the pyrite electrode were compared with those obtained using a platinum electrode (Fe³⁺), a Cu ion selective electrode (Cu²⁺) and a Hg electrode (Hg²⁺). Accurate and reproducible results with good agreement were obtained, but higher potential changes at the TEP were obtained using the pyrite electrode. In the course of the titration the potential was established within less than 1 min, whereas at the TEP it was within about 2–3 min. The potential changes at the TEP were in the range from 60 to 200 mV per 0.1 ml EDTA, according to the stability constant of the complex formed. The highest potential changes, ranging from 160 to 200 mV, were obtained in the titration of iron(III) at pH 3.59. Reverse titration was also performed and accurate and reproducible results were obtained. Moreover, titration of halogenide and thiocyanate with standard mercury(II) solutions, as well as cyanide with silver(I) solution, were performed and accurate and reproducible results were again obtained. Received: 20 February 1998 / Accepted: 19 November 1999     

Thermal decomposition of hydrotalcite with hexacyanoferrate(II) and hexacyanoferrate(III) anions in the interlayer

The mechanism for the decomposition of hydrotalcite remains unsolved. Controlled rate thermal analysis enables this decomposition pathway to be explored. The thermal decomposition of hydrotalcites with hexacyanoferrate(II) and hexacyanoferrate(III) in the interlayer has been studied using controlled rate thermal analysis technology. X-ray diffraction shows the hydrotalcites have a d(003) spacing of 10.9 and 11.1 Å which compares with a d-spacing of 7.9 and 7.98 Å for the hydrotalcite with carbonate or sulphate in the interlayer. Calculations show dehydration with a total loss of 7 moles of water proving the formula of hexacyanoferrate(II) intercalated hydrotalcite is Mg₆Al₂(OH)₁₆[Fe(CN)₆]_0.5·7H₂O and 9.0 moles for the hexacyanoferrate(III) intercalated hydrotalcite with the formula of Mg₆Al₂(OH)₁₆[Fe(CN)₆]_0.66·9H₂O. CRTA technology indicates the partial collapse of the dehydrated mineral. Dehydroxylation combined with CN unit loss occurs in two isothermal stages at 377 and 390°C for the hexacyanoferrate(III) and in a single isothermal process at 374°C for the hexacyanoferrate(III) hydrotalcite.     

Determination of Fe(II)-Fe(III) and Fe(III)-Ni(II) by the two-component potentiometric complexometric titration

Summary The two-component complexometric potentiometric titration has been applied to the simultaneous determination of Fe(III) and Fe(II), and of Fe(III) and Ni(II) in solution. In each case the two analytes were determined by reading the end-points directly from the titration curve. The end-points are determined in a sense arbitrarily, but they are repeatable and easy to be detected precisely. However, the apparent (found) analytical results are biased. They are effectively corrected with the use of a set of two calibration equations (uncomplete second degree polynomials), which approximate the relationship between found endpoints and true concentrations of analytes in solution. The regression coefficients in the equations are determined on the basis of titration data obtained for standard solutions whose compositions correspond to a 2² factorial. Permanent address: Department of Analytical Chemistry, Jagiellonian University, Krakow     

PH电位法研究水杨醛缩氨基硫脲与铜(II)、锌(II)、镍(II)、钴(II)、锰(II)及镉(II)的相互作用

本文为了进一步了解具有生物活性的木杨醛缩氨基硫脲在溶液中与常见金属离子的作用本质, 在半微量恒温滴定池上用PH电位法研究了该物质与铜(II)、锌(II)、镍(II)、钴(II)、锰(II)及镉(II)等二价金属离子的配位作用.     

Catalytic amperometric and catalytic constant-current potentiometric titrations of silver(I), palladium(II) and mercury(II)

Amperometry and constant-current potentiometry were used to follow the course of catalytic titrations of silver(I), palladium(II), and mercury(II) with potassium iodide. The Ce(IV)As(III) and Ce(IV)Sb(III) systems in the presence of sulphuric acid were used as indicator reactions. The possibilities of application of platinum, palladium, gold, graphite, and glassy-carbon indicator electrodes were investigated. Graphite appeared to be somewhat more advantageous than the other electrode materials. The effect of concentration of the components of the indicator reactions, the presence of organic solvents and acids on the shape of the catalytic titration curves was studied. Amounts of 30-3000 mug of silver(I) nitrate, 90-900 mug of palladium(II) chloride, 130-1300 mug of mercury(II) chloride, and 150-1500 mug of mercury(II) nitrate were determined with a relative standard deviation less than 1.0%. The results obtained were in good agreement with those of comparable methods. The catalytic titration method developed was applied to determination of mercury in Unguentum Hydrargyri.     

火试金富集--自动电位滴定法测定粗碲中的银含量

粗碲是由铜、铅、锌冶炼带来的副产品,其中含有大量的金、银等贵金属。快速准确检测粗碲中银含量,具有十分重要的意义。样品预先采用硫酸溶解,还原沉淀金、银,过滤分离大部分的铋、硒、碲等元素,经配料、高温熔融,熔融态的金属铅捕集试料中的贵金属形成铅扣,试料的其他物质与熔剂生成易熔性熔渣。将铅扣灰吹,得金银合粒,清除合粒表面粘附的杂质,经硝酸分金,用硫氰酸钾滴定法测定银量。银的加标回收率在99.5%～101%,相对标准偏差(RSD)小于5%。方法速度快,稳定性好,适用于粗碲中银含量的测定。