Reducing agents equivalent mass

The equivalent mass of an oxidizing or reducing agent for a particular reaction is equal to its molar mass divided by the total number of moles of electrons gained or lost when the reaction of one mole occurs. A given... 

Equivalent masses are so defined because equal numbers of equivalents of two substances react exactly with each other. This is true for neutralization because one H+ neutralizes one OH-, and for oxidation-reduction reaction because the number of electrons lost by the reducing agent equals the number gained by the oxidation agent (electrons cannot be eliminated—by the law of conservation of matter). 

The mass of a cystine-containing protein will be two mass units smaller than the equivalent cysteine-containing protein because two —SH groups are oxidized to —S—S—. To confirm this finding, it would be necessary to treat the protein with a reducing agent and compare the masses of the reduced and nonreduced samples. 

Equivalent masses of oxidizing agents and reducing agents react exactly with one another, since they involve the taking up or giving up of the same number of electrons. 

What fraction of the formula mass is the oxidation equivalent mass or reduction equivalent mass of each of the oxidizing or reducing agents in the equations of Exercise 11-7 ... 

A sample of impure tin of mass 0.535 g is dissolved in strong acid to give a solution of Sn. The solution is then titrated with a 0.0448 M solution of NO3 , which is reduced to NO(g). The equivalence point is reached upon the addition of 0.0344 L of the NO3 solution. Find the percent by mass of tin in the original sample, assuming that it contains no other reducing agents. 

The standard redox potential is 1.14 volts the formal potential is 1.06 volts in 1M hydrochloric acid solution. The colour change, however, occurs at about 1.12 volts, because the colour of the reduced form (deep red) is so much more intense than that of the oxidised form (pale blue). The indicator is of great value in the titration of iron(II) salts and other substances with cerium(IV) sulphate solutions. It is prepared by dissolving 1,10-phenanthroline hydrate (relative molecular mass= 198.1) in the calculated quantity of 0.02M acid-free iron(II) sulphate, and is therefore l,10-phenanthroline-iron(II) complex sulphate (known as ferroin). One drop is usually sufficient in a titration this is equivalent to less than 0.01 mL of 0.05 M oxidising agent, and hence the indicator blank is negligible at this or higher concentrations. 

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