Sodium ion activity

The activity coefficient for the counterions was taken to be a constant value of 0.862. This value was derived from the experimental value of 0.745 for NaCJl, which was reported by Moore (20). The sodium ion activity coefficient was obtained as the square root of the sodium chloride activity coefficient. 

To investigate whether the Na+ is trapped by the resin or is carried through in a specific interaction, several model compounds were studied in NaOH solution. The decrease in activity was measured with a specific-ion electrode, and the results are recorded in Table V. A relatively small decrease in sodium ion activity in o-hydroxybenzyl alcohol was noted. 

Table V. Sodium Ion Activity with Model Compounds (25°C)...

Based on sodium ion activities [16] and conductance studies [17,18] it appears... 

NaJATPasc sodium ion activated ATPase (also Na-ATPase, NaATPase)... 

A cation-sensitive electrode is used to determine the activity of calcium in the presence of sodium. The potential of the electrode in 0.0100 M CaCl2 measured against an SCE is +195.5 mV. In a solution containing 0.0100 M CaCl2 and 0.0100 M NaCl, the potential is 201.8 mV. What is the activity of calcium ion in an unknown solution if the potential of the electrode in this is 215.6 mV versus SCE and the sodium ion activity has been determined with a sodium ion-selective electrode to be 0.0120 M Assume Nemstian response. 

J.R. Wyllie and H.W. Patnode, The development of membranes from artificial cation-exchange materials with particular reference to the determination of sodium-ion activity, J. Phys. Chem., 1950, 54, 204. 

Ion-selective electrodes are also widely employed for the potentiometric determination of the sodium ion activity and concentration in nonseparated biological samples, both in vitro and in vivo. Particularly, the feasibility of their use in continuous as well as in situ applications makes them attractive. 

Early support for the role of polymer hydrophobicity came from a study (158) of the interaction of a series of nonionizable polypeptides (poly-DL-alanine and three derivatives of poly-L-glutamine) with SDS. Strongest interaction, as judged from the lowest T l value (from dye solubilization and electrical conductivity measurements) and highest ionic dissociation (a, from sodium ion activity measurements) of the complex, was obtained with the most hydrophobic member, viz., poly-DL-alanine, and vice versa. 

The cell for determining sodium-ion activity (calibrated as concentration) is described by... 

Strong association of Na ion with the polystyrenesulfonate anion (or, of Cl ion with the polycation). The activity coefficient of sodium ion, is strongly decreased from its value in pure NaCl solutions of the same concentration as has been demon-stated by measurements with single-ion electrodes. [3, 25] These measurements indicate that the sodium ion activity coefficient is ca. 0.3 [3] or 0.435 [25] for solutions of sodium polyvinylsulfate or sodium polymethylstyrenesulfonate at m = 0.1, respectively. The smaller of these two 71 1 + values is almost the same as y+ for Trace concentrations of NaCl in the presence of 0.1 m NaPSS (Figure 11). This near equality would appear to require that the activity coefficient of chloride ion be approximately the same as that for Na" ion, or, marked disagreement... 

EMF of a sodium-selective measuring cell and the corresponding sodium ion activity and concentration [77]. Figure 24 summarizes the different selectivities of a cation-sensitive glass [78]. 

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