Ions ionic strength

Recall from transition state theory that the rate of a reaction depends on kg (the catalytic rate constant at infinite dilution in the given solvent), the activity of the reactants, and the activity of the activated complex. If one or more of the reactants is a charged species, then the activity coefficient of any ion can be expressed in terms of the Debye-Htickel theory. The latter treats the behavior of dilute solutions of ions in terms of electrical charge, the distance of closest approach of another ion, ionic strength, absolute temperature, as well as other constants that are characteristic of each solvent. If any other factor alters the effect of ionic strength on reaction rates, then one must look beyond Debye-Hiickel theory for an appropriate treatment. 

Propose an experiment that would allow you to purify GOT with the use of a DEAE (diethy-laminoethyl) cellulose column rather than with a CMC (carboxymethylcellulose) column. The pi of GOT is —6.0. Include in your answer a description of the buffer system that you would use (buffering ions, ionic strength, pH) for loading GOT on the column and for eluting GOT from the column. 

Activity coefficient Activity coefficient of the calcium ion Activity coefficient of the carbonate ion Activity coefficient of the hydrogen ion Activity coefficient of the bicarbonate ion Activity coefficient of the hydroxyl ion Ionic strength Mass density of CaC03... 

Influence of Small Ions Ionic Strength (Figure 2.22) Debye-Huckel Theory... 

The stationary phase type for a particular separation is selected based on the requirement that the sample ions and immobilized charged groups of the stationary phase must have complementary properties. The separation is then optimized by adjusting the buffer composition (identity of competing ion, ionic strength, pH), temperature, flow... 

Ions (ionic strength) Sulfonated polystyrene, sulfonated dextran [34]... 

Every PVC membrane can absorb water from the water phase, which causes turbidity of membrane. This phenomenon was studied by Harrison et a/. [31,32]. It was found that water is not evenly distributed in the membrane, but there exists a water-rich area near the electrode surface. The water content in a typical PVC membrane (33% PVC, 67% bis(2-ethylhexyl) adipate (DOA)) is approx. 0.6 w/w the membrane density is 1.08 g/cm This value is approximated, since it depends on the membrane composition (hydrophilic components will cause higher adsorption of water) and the concentration of ions (ionic strength) in the water phase. 

Harkins spreading coefficient of a hqnid on another, ionic strength of a solution of ions, ionic strength in relation to molality valnes. moments of inertia. 

Features Affected by hard water ions, ionic strength, temp. 

For example, van den Tempel [35] reports the results shown in Fig. XIV-9 on the effect of electrolyte concentration on flocculation rates of an O/W emulsion. Note that d ln)ldt (equal to k in the simple theory) increases rapidly with ionic strength, presumably due to the decrease in double-layer half-thickness and perhaps also due to some Stem layer adsorption of positive ions. The preexponential factor in Eq. XIV-7, ko = (8kr/3 ), should have the value of about 10 " cm, but at low electrolyte concentration, the values in the figure are smaller by tenfold or a hundredfold. This reduction may be qualitatively ascribed to charged repulsion. 

In determining the values of Ka use is made of the pronounced shift of the UV-vis absorption spectrum of 2.4 upon coordination to the catalytically active ions as is illustrated in Figure 2.4 ". The occurrence of an isosbestic point can be regarded as an indication that there are only two species in solution that contribute to the absorption spectrum free and coordinated dienophile. The exact method of determination of the equilibrium constants is described extensively in reference 75 and is summarised in the experimental section. Since equilibrium constants and rate constants depend on the ionic strength, from this point onward, all measurements have been performed at constant ionic strength of 2.00 M usir potassium nitrate as background electrolyte . 

Table 2.6. Equilibrium constants from complexation of 2.4a, 2.4b, and 2.4d to different metal ions (Kj) and second-order rate constants for the Diels-Alder reaction of these complexes with 2 (%cd) in water at 2.00 M ionic strength and 25°C. ...

Several features of equation 6.50 deserve mention. First, as the ionic strength approaches zero, the activity coefficient approaches a value of one. Thus, in a solution where the ionic strength is zero, an ion s activity and concentration are identical. We can take advantage of this fact to determine a reaction s thermodynamic equilibrium constant. The equilibrium constant based on concentrations is measured for several increasingly smaller ionic strengths and the results extrapolated... 

Procedure. Prepare a set of external standards containing 0.5 g/L to 3.0 g/L creatinine (in 5 mM H2SO4) using a stock solution of 10.00 g/L creatinine in 5 mM H2SO4. In addition, prepare a solution of 1.00 x 10 M sodium picrate. Pipet 25.00 mL of 0.20 M NaOH, adjusted to an ionic strength of 1.00 M using Na2S04, into a thermostated reaction cell at 25 °C. Add 0.500 mL of the 1.00 x 10 M picrate solution to the reaction cell. Suspend a picrate ion-selective electrode in the solution, and monitor the potential until it stabilizes. When the potential is stable, add 2.00 mL of a... 

The potential of the ion-selective electrode actually responds to the activity of picrate in solution. By adjusting the NaOH solution to a high ionic strength, we maintain a constant ionic strength in all standards and samples. Because the relationship between activity and concentration is a function of ionic strength (see Chapter 6), the use of a constant ionic strength allows us to treat the potential as though it were a function of the concentration of picrate. 

Accuracy and Interpretation of Measured pH Values. The acidity function which is the experimental basis for the assignment of pH, is reproducible within about 0.003 pH unit from 10 to 40°C. If the ionic strength is known, the assignment of numerical values to the activity coefficient of chloride ion does not add to the uncertainty. However, errors in the standard potential of the cell, in the composition of the buffer materials, and ia the preparatioa of the solutioas may raise the uacertaiaty to 0.005 pH unit. 

Because they are weak acids or bases, the iadicators may affect the pH of the sample, especially ia the case of a poorly buffered solution. Variations in the ionic strength or solvent composition, or both, also can produce large uncertainties in pH measurements, presumably caused by changes in the equihbria of the indicator species. Specific chemical reactions also may occur between solutes in the sample and the indicator species to produce appreciable pH errors. Examples of such interferences include binding of the indicator forms by proteins and colloidal substances and direct reaction with sample components, eg, oxidising agents and heavy-metal ions. 

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