Buffer solutions properties

Because the ionic product of water = [H ] [OH ] = 1.04 x 10" at 25°C, it follows that pH = 14 - pOH. Thus, a neutral solution (e.g., pure water at 25°C) in which [H j = [OH ] has a pH = pOH = 7. Acids show a lower pH and bases a higher pH than this neutral value of 7. The hydrogen ion concentrations can cover a wide range, from -1 g-ion/liter or more in acidic solutions to -lO" " g-ion/liter or less in alkaline solutions [53, p. 545]. Buffer action refers to the property of a solution in resisting change of pH upon addition of an acid or a base. Buffer solutions usually consist of a mixture of a weak acid and its salt (conjugate base) or of a weak base and its salt (conjugate acid). 

Apparently, no bottles of aqueous ammonia are present in the laboratory, so the components of the buffer solution must come from the salts. The technician needs an ammonium salt with a counter anion that has no acid-base properties. Ammonium chloride (NH4 Cl) would be an appropriate choice. This salt contains the conjugate acid, NH4, and the technician can generate NH3 by adding strong base to the ammonium chloride solution NH4 ((2 q) + OH ((2 q) NH3((3 q) + H2 0(/)... 

A buffer solution is a solution of a weak acid and its conjugate base or a weak base and its conjugate acid. The main property of a buffer solution is its resistance to changes in its pH despite addition of small quantities of strong acid or strong base. The student must know the following three things about buffer solutions ... 

The tetracyclines are well known for their ability to form complexes with polyvalent cations. This property changes their solubility characteristics in the mobile solvents and often results in troublesome streaking. To overcome this difficulty, Selzer and Wright used paper dipped in Mcllvaine s buffer (pH 3.5) which contains citrate ions capable of binding the metallic ions. The chromatograms were developed with a mixture of nitromethane, chloroform, and pyridine (20 10 3) on paper still damp from the treatment with the buffer solution. 

Fig. 5 Chemical structure (a), absorption (a) and emission (b) spectra of POWT in different buffer solutions pH 2 (open diamond), pH 5 (open square), pH 8 (triangle) and pH 11 (x).(c) The charge of the zwitter-ionic side chain, schematic drawing of proposed backbone conformations and optical properties of POWT at different pH [9]...

Anions and uncharged analytes tend to spend more time in the buffered solution and as a result their movement relates to this. While these are useful generalizations, various factors contribute to the migration order of the analytes. These include the anionic or cationic nature of the surfactant, the influence of electroendosmosis, the properties of the buffer, the contributions of electrostatic versus hydrophobic interactions and the electrophoretic mobility of the native analyte. In addition, organic modifiers, e.g. methanol, acetonitrile and tetrahydrofuran are used to enhance separations and these increase the affinity of the more hydrophobic analytes for the liquid rather than the micellar phase. The effect of chirality of the analyte on its interaction with the micelles is utilized to separate enantiomers that either are already present in a sample or have been chemically produced. Such pre-capillary derivatization has been used to produce chiral amino acids for capillary electrophoresis. An alternative approach to chiral separations is the incorporation of additives such as cyclodextrins in the buffer solution. 

Sorensen is usually considered to be the first to have realized the importance of hydrogen ion concentration in cells and in the solutions in which the properties of cell components were to be studied. He is also credited with the introduction of the pH scale. Electrochemistry started at the end of the nineteenth century. By 1909, Sorensen had introduced a series of dyes whose color changes were related to the pH of the solution, which was determined by the H+ electrode. The dyes were salts of weak acids or weak bases. He also devised simple methods for preparing phosphate buffer solutions covering the pH range 6-8. Eventually buffers and indicators were provided covering virtually the whole pH range. 

The Henderson-Hasselbalch equation may be employed in calculations relating to the properties and effects of buffer solutions (see Box 4.8). 

The LOST properties of P(MAA)-r-(OEGMA47s) and P(MAA)-r-(OEGMAnoo) libraries were determined in buffer solutions with different pH values. As illustrated in Fig. 14, the copolymer library of P(MAA)-r-(OEGMA47s) revealed cloud points from 25 to 90 °C at pH values of 2 and 4, respectively. It was mentioned... 

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