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What are the applications of electrochemical series (or electromotive series)? |
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Answer» Solution : The applications of electrochemical series (or electromotive series) are as follows : (1) Relative strength of oxidising agents in terms of `E_("red")^(0)` values : The `E_("red")^(0)` valueisa measure of the tendency of the species to be reduced i.e. to accept electrons and act as an oxidising agent. The species mentioned on left hand side of the half reactions are oxidising agents. The substances in the upper positions in the series and hence in the upper left side of the half reactions have large positive Ered values hence are stronger oxidising agents. For example, `F_(2+), Ce^(4+) , Au^(3+)`, etc. As we move down the series, the oxidising power decreases. Hence from the position of the elements in the electrochemical series,oxidising agents can be selected. (2) Relative strength of reducing agents in terms of `E_("red")^(0)`values: The LOWER `E_("red")^(0)`value meanslowertendencyto accpetelectrons but higher tendency to lose electrons. The tendency for reverse REACTION or oxidation increases as `E_("red")^(0)` becomes morenegativeand wemovetowrads the lowerside of THESERIES. For example, Li, K , Al etc.are goodreducingagent . (3) Identifying the spontaneous direction of reaction : From the standard reduction potentials, Eed the spontaneity of a redoxreaction can be determined. The difference between `E_("red")^(0)`value for any towelectrodes represenetscell potenital `E_("cell")^(0)` , constituted by them. If `E_("cell")^(0)` is positive then the reaction is spontaneous while if`E_("cell")^(0)` is negative the reaction is non-spontaneous . For example `E_(Mg^(2+)//Mg)^(2)` and `E_(AG^(+)//Ag)^(0)` havevalues - 2.37V and 0.8 V respectively. TheMg will be a betterreducingagentthanAg. ThereforeMgcan reduce `Ag^(+)` to Ag. The correspondingreactionwill be . `Mg_((s)) + 2Ag_((aq))^(+) + 2Ag_((s))` `E_("cell")^(0)=E_(Ag^(+)//Mg)^(0) = 0.8 -(-2.37)` = 3.17V Therefore abovereactionin theforward directionwill bespontaneouswhilein thereversedirection will benon-spontaneous. since forit `E_("cell")^(0) = - 3.17` V. (4) Calculation of standard cell potential`E_("cell")^(0)` From theelectrochemical series, the standard cell potential, `E_("cell")^(0) ` form the `E_("red")^(0) ` valuefor thehalfreactions givescan becalculate. Forexample `Zn^(2+) + 2e^(-) to Zn_((s)) ""E_(Zn^(2+)//Zn)^(0) = - 0.76V` `Cu^(2+) + 2e^(-) toCu_((s)) "" E_(Cu^(2+)//Cu)^(0) = - 0.34 V` For thecell, `Zn|Zn_((aq))^(2+) (1M) || Cu_((aq))^(2+) (1M) |Cu` `E_("cell")^(0) = E_(underset("(cathode)")(Cu^(2+)//Cu))^(0) -E_(underset("(andoe)")(Zn^(2+)//Zn))^(0)` `= 0.34-(-0.76)` = 1.1 |
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