The Conditions Needed for a Buffer to Set the pH in a System

It is a known fact that buffer systems are widely used in industry and in diverse laboratories to maintain the pH of a system within desired limits, occasionally narrow. Hence, the aim of the present work is to study the buffer capacity and buffer efficacy in order to determine the useful conditions to impose the pH on a given system. This study is based on the electroneutrality and component balance equations for a mixture of protons polyreceptors. The added volume equations were established, V, for strong acids or bases, as well as the buffer capacity equations with dilution effect, β dil, and the buffer efficacy, ε, considering that the analyte contains a mixture of the species of the same polyacid system or of various polyacid systems. The ε index is introduced to define the performance of a buffer solution and to find out for certain, whether the buffer is adequate or not to set the pH of a system, given the proper conditions and characteristics

Momento Económico (34-35)

En este número Temas de hoy. 21 El Pacto de Solidaridad Económica (PSE) y la inflación en México Fausto Burgueño Lomelí. 3/ El pacto, hacia la rectoría trasnacional: significa la expropiación del salario Mario J. Zepeda. 4/ El PSE: Desinflación con más estancamiento lfigenia Martínez, 5/ Inflación y PSE Arturo Guillén Romo, 7/ Qué es y cómo surgió el PSE Magdalena Galindo, 9/ El PSE o después del pueblo ahogado...tapen el pozo Victor M. Bernal Sahagún, 13/ Monetarismo en el pacto lrma Manrique Campos, 14/ El pacto contra inflación: segundo round Emilio Romero Polanco. 11/ Aspectos monetarios y cambiarios del PSE Alma Chapoy Bonifaz, 18/ Financiamiento externo y PSE Andrés Blancas Neria, 23/ Apertura comercial y privatización: dos caras del proyecto del gran capital Patricia Olave C. 28

Cálculo del coeficiente de difusión del Zn en un disolvente eutéctico profundo mediante técnicas electroquímicas

En el presente trabajo se llevó a cabo la determinación electroquímica del coeficiente de difusión del Zn²⁺, en un disolvente eutéctico profundo compuesto por cloruro de colina y urea, en una relación molar de 1:2, a una temperatura de 70 °C. Para ello se emplearon las técnicas electroquímicas de voltamperometría cíclica y cronoamperometría. A partir de los transitorios potenciostáticos de corriente, de la ecuación de Cottrell y mediante el análisis de las coordenadas del máximo, se calculó el valor para D= 4.76x10-⁸ cm²s-¹ y D= 6.71x10-⁸ cm²s-¹, respectivamente.In the present work it was carried out the electrochemical determination of the diffusion coefficient of Zn²⁺, in a deep eutectic solvent composed of choline chloride and urea in a molar ratio of 1:2, at a temperature of 70°C. For this, the electrochemical techniques of cyclic voltammetry and chronoamperometry were used. From potentiostatic current transients and Cottrell equation, the value for D=4.76x10-⁸ cm²s-¹ and D=4.76x10-⁸ cm²s-¹ was calculated, respectively

Cuantificación electroquímica de la superficie electroactiva de nanopartículas de Au soportadas sobre ITO a diferentes monocapas mediante electrodepósito de Cu a subpotencial

En el presente trabajo, se llevó a cabo la determinación del área superficial activa, ASA, de nanopartículas de Au, AuNPs, soportadas sobre ITO, a diferentes monocapas de AuNPs. Para llevar a cabo lo anterior, se formaron monocapas de AuNPs sobre la superficie del electrodo de ITO a través de un policatión, la poli L-lisina, PLL, entre cada capa. Una vez formada cada monocapa, se lleva a cabo el proceso de electrodepósito de Cu a subpotencial, UPD, en una disolución acuosa de Cu²⁺, empleando las técnicas electroquímicas de voltamperometría cíclica y cronoamperometría. Del análisis de los transitorios potenciostáticos de corriente se determinó la carga eléctrica involucrada en el proceso de formación de cada monocapa, y a partir de esta se determinó el ASA con respecto a las monocapas 1, 2 y 5.The present work was conducted to determine the active surface area, ASA, of Au nanoparticles, AuNPs, supported on ITO, to different monolayers AuNPs. To perform the above, AuNPs monolayers on the surface of ITO electrode is formed through a polycation, poly L-lysine, PLL, between each layer. Each monolayer once formed, is held the Cu electroplating process underpotential, UPD, in an aqueous solution of Cu²⁺, using electrochemical techniques such as cyclic voltammetry and chronoamperometry. Analysis potentiostatic current transient electrical load involved in the formation of each monolayer was determined, and from this, the ASA was determined over monolayers 1, 2 and 5

Prácticas del laboratorio de metalurgia I : cristales perfectos e imperfectos : para la carrera de ingeniería metalúrgica

1 archivo PDF (66 páginas) ; 2a ed.Prácticas para servir como una guía en el laboratorio de metalurgia I, que es el complemento del curso de cristales perfectos e imperfectos que se imparte para la carrera de Ingeniería Metalúrgica

Effect of Zirconia Nanoparticles in Epoxy-Silica Hybrid Adhesives to Join Aluminum Substrates

This research presents the interaction of the epoxy polymer diglicydil ether of bisphenol-A (DGEBA) with silica (SiO2) nanoparticles plus zirconia (ZrO2) nanoparticles obtained via the sol-gel method in the synthesis of an epoxy-silica-zirconia hybrid adhesive cured with polyamide. ZrO2 nanoparticles were added to the epoxy-silica hybrid adhesive produced in situ to modify the apparent shear strength of two adhesively bonded aluminum specimens. The results showed that the addition of different amounts of ZrO2 nanoparticles increased the shear strength of the adhesively bonded aluminum joint, previously treated by sandblasting, immersion in hot water and silanized with a solution of hydrolyzed 3-glycidoxipropyltrimethoxysilane (GPTMS). The morphology and microstructure of the nanoparticles and aluminum surfaces were examined by scanning electron microscopy (SEM), and elemental analysis was performed with the Energy-dispersive X-ray spectroscopy (EDS) detector; the chemical groups were investigated during the aluminum surface modification using Fourier transform infrared spectroscopy (FTIR)

An Exact Method to Determine the Conductivity of Aqueous Solutions in Acid-Base Titrations

Several works in the literature show that it is possible to establish the analytic equations to estimate the volume V of a strong base or a strong acid (Vb and Va, resp.) being added to a solution of a substance or a mix of substances during an acid-base titration, as well as the equations to estimate the first derivative of the titration plot dpH/dV, and algebraic expressions to determine the buffer β capacity with dilution βdil. This treatment allows establishing the conditions of thermodynamic equilibria for all species within a system containing a mix of species from one or from various polyacid systems. The present work shows that it is possible to determine exactly the electric conductivity of aqueous solutions for these Brønsted acid-base titrations, because the functional relation between this property and the composition of the system in equilibrium is well known; this is achieved using the equivalent conductivity λi values of each of the ions present in a given system. The model employed for the present work confirms the experimental outcomes with the H2SO4, B(OH)3, CH3COOH, and H3PO4 aqueous solutions’ titration

Electrochemical Quantification of the Antioxidant Capacity of Medicinal Plants Using Biosensors

The working area of a screen-printed electrode, SPE, was modified with the enzyme tyrosinase (Tyr) using different immobilization methods, namely entrapment with water-soluble polyvinyl alcohol (PVA), cross-linking using glutaraldehyde (GA), and cross-linking using GA and human serum albumin (HSA); the resulting electrodes were termed SPE/Tyr/PVA, SPE/Tyr/GA and SPE/Tyr/HSA/GA, respectively. These biosensors were characterized by means of amperometry and EIS techniques. From amperometric evaluations, the apparent Michaelis-Menten constant, Km′, of each biosensor was evaluated while the respective charge transfer resistance, Rct, was assessed from impedance measurements. It was found that the SPE/Tyr/GA had the smallest Km′ (57 ± 7) µM and Rct values. This electrode also displayed both the lowest detection and quantification limits for catechol quantification. Using the SPE/Tyr/GA, the Trolox Equivalent Antioxidant Capacity (TEAC) was determined from infusions prepared with “mirto” (Salvia microphylla), “hHierba dulce” (Lippia dulcis) and “salve real” (Lippia alba), medicinal plants commonly used in Mexico