Chloride reference change values

The most widely used reference electrode, due to its ease of preparation and constancy of potential, is the calomel electrode. A calomel half-cell is one in which mercury and calomel [mercury(I) chloride] are covered with potassium chloride solution of definite concentration this may be 0.1 M, 1M, or saturated. These electrodes are referred to as the decimolar, the molar and the saturated calomel electrode (S.C.E.) and have the potentials, relative to the standard hydrogen electrode at 25 °C, of 0.3358,0.2824 and 0.2444 volt. Of these electrodes the S.C.E. is most commonly used, largely because of the suppressive effect of saturated potassium chloride solution on liquid junction potentials. However, this electrode suffers from the drawback that its potential varies rapidly with alteration in temperature owing to changes in the solubility of potassium chloride, and restoration of a stable potential may be slow owing to the disturbance of the calomel-potassium chloride equilibrium. The potentials of the decimolar and molar electrodes are less affected by change in temperature and are to be preferred in cases where accurate values of electrode potentials are required. The electrode reaction is... 

Frensdorff (3) has determined log K values for the reaction in methanol of several cyclic polyethers of varying ring size and numbers of donor atoms with Na+, K+, and Cs+ (all chlorides). The log K values are plotted in Fig. 2 where several trends are evident. The relationship between ring size and cation size which has been referred to as the selectivity order changes from Na+>K+ for dicyclohexyl-14-crown-4 to Na+ K+>Cs+ for cyclohexyl-15-crown-5, to K+ >Cs+ Na+ for dibenzo-... 

As seen from the data in Table 7-4 (abstracted from frequencies provided in Appendix A7) symmetric methyl group CH stretching frequencies change with substitution. The smallest value is for methylamine (chosen as the reference compound) and the largest is for methyl chloride. (Ethane has been excluded from this comparison as the symmetric stretch here involves all six hydrogens.)... 

Put a piece of indicator paper (a universal indicator) on a watch glass and wet it with a sodium carbonate solution. Note the change in the indicator colour, compare it with a reference, and determine the pH of the sodium carbonate solution. Perform similar experiments with aluminium and sodium chlorides. Use the pH values obtained to calculate the hydrogen ion concentrations in the studied solutions. 

Bates indicated that the soundest procedure for experimentally establishing a practical scale for pH in a given solvent requires that the hydrogen gas electrode and the silver-silver chloride electrodes be thermodynamically reversible and stable in the solvent system, the glass (or other) electrode respond in a Nernstian way, and the liquid-junction potential be little affected by change in acidity of the solution. A reference value for pH should be selected that is close to that of the solution to be measured and that gives rational meaning to pH values for the solutions examined. 

Crystalline yttrium selenite was prepared and its enthalpy of dissolution in the solvent HCl(aq, 1 18.5), denoted sin, as well as the enthalpy of dissolution of selenious acid in the same solvent were determined. The enthalpy of dissolution in the medium of yttrium chloride, which is needed as an auxiliary datum, was not measured. The review has therefore estimated the enthalpy change of Reaction 3 in Table A-63 from dissolution data of YCl3(cr) in HCl(aq) in [88X1A/ZHU] and [970PP/EHR]. The evaluation also uses the mean value of the enthalpy of formation of YCl3(cr) in these references. 

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