Electrolyte Solutions Salt solutions used as reactants or electrolytes in aqueou

Question

Electrolyte Solutions
Salt solutions used as reactants or electrolytes in aqueous electrochemical cells very often employ sodium, potassium, nitrate, or sulfate salts as the counter-ions for the active cation or active anion of each half-cell.

a) Explain why the sodium ion or potassium ion are not reduced in aqueous solution
b) Explain why nitrate anions will not be oxidized in aqueous elctrochemical cells.
c) Explain why sulfate anions will not be oxidized, but the sulfite ion could be oxidized in aqueous electrochemical cells.

Explanation / Answer

a) The reduction of sodium is more difficult than the reduction of water. ENa+ = -2,27 V; EH2O = -1,23 V. Sodium and potassium only have 1 s electron, when they loses it, they acquire noble gas electronic configuration and it is very stable.

b) NO3- the negative charge is stabilized by resonance betwen the atoms that support negative charges very well, it is a very stable specie.

c) SO3- can be oxidized to SO4- because the latter is by far more stable, the charge is stabilized by resonance in 4 oxygen atoms instead of three.

Its all about thermodynamics, flow of electron andstabilization.

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