Standard potential of tin

It is of interest to note that if the equilibrium constant of the system consisting of two metals and their simple ions could be determined experimentally and the standard potential of one of them were known, the standard potential of the other metal could be evaluated by means of equation (34). This method was actually used to obtain the standard potential of tin recorded in Table XLIX. Finely divided tin and lead were shaken with a solution containing lead and tin perchlorates until equilibrium was attained the ratio of the concentrations of lead and stannous ions in the solution was then determined by analysis. The standard potential of lead being known, that of tin could be calculated. 

The Standard Potential of Tin. Direct determinations of the standard potential of tin are of doubtful accuracy. The potential can however be readily computed from the standard potential of lead and a knowledge of the equilibrium... 

The use of a chemical equilibrium has already been illustrated in the determination of the standard potential of tin, page 25S. In the case under discussion the reaction... 

On the outside of a tinned container, tin is cathodic to iron, in accord with the standard potential of tin equal to -0.136 V compared to -0.440 V for iron. On the inside, however, tin is almost always anodic to iron, and hence, tin cathodically protects the base steel. This fortunate reversal of potential occurs because stannous ions, Sn +, are complexed by many food products that greatly reduce Sn + activity, resulting in a change in corrosion potential of tin in the active direction (see Section 3.8). On the inside of the can, the corrosion reaction for tin is... 

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See also in sourсe #XX -- [ ]

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