Question

Explain the following:
(i) Nernst Equation.
(ii) Aqua regia.

Answer 1

(i) Nernst Equation gives the dependence of cell potential (and elecrode potential) on temperature, solute concentration and partial pressure of gases.
$E=E^o-\frac{RT}{nF}lnQ$
$E=E^o-\frac{2.303RT}{nF}logQ$
$Q=\frac{\text{[products]}}{\text{reactants}}=$ reaction quotient.
$E=$ cell potential ( or electrode potential)
$E^o$ standard cell potential ( or standard electrode potential)
$R=$ ideal gas constant $=$ 8.314 J/mol/K
$T=$ absolute temperature
$n=$ Number of moles of electrons that participate in the reaction.
$F=$ faraday $=$ 96500 C/mol electrons.
At 25 deg C $\frac{2.303RT}{nF}=0.0592$
$E=E^o-\frac{0.0592}{n}logQ$
(ii) Aqua regia.
It is a mixture of nitric acid (1 mole) and hydrochloric acid (3 moles).
It dissolves the noble metals gold and platinum.