Short Answer TypeThe resistance of a conductivity cell filled with 0.1 mol L-1 KCl solution is 100 . If the resistance of the same cell when filled with 0.02 mol L-1 KCl solution is 520
, calculate the conductivity and molar conductivity of 0.02 mol L-1 KCl solution. The conductivity of 0.1 mol L-1 KCl solution is 1.29x 10-2
-1cm-1
State Faraday's first law of electrolysis. How much charge in terms of Faraday is required for the reduction of 1 mol of Cu2+ to Cu.
Calculate emf of the following cell at 298 K: Mg(s) | Mg2+(0.1 M) || Cu2+ (0.01) | Cu(s)
[Given E0 cell = +2.71 V, 1 F = 96500 C mol-1]
Account for the following:
(i) Mn2+ is more stable than Fe2+ towards oxidation to +3 state.
(ii) The enthalpy of atomization is lowest for Zn in 3d series of the transition elements.
(iii) Actinoid elements show a wide range of oxidation states.
(i) Name the elements of 3d transition series that show a maximum number of oxidation states. Why does this happen?
(ii) Which transition metal of 3d series has positive E0 (M2+/M) value and why?
(iii) Out of Cr3+ and Mn3+, which is a stronger oxidising agent and why?
(iv) Name a member of the lanthanoid series that is well-known to exhibit +2 oxidation state.
(v) Complete the following equation: MnO4- + 8H+ + 5e- -->
1) In 3d-series of transition metals, manganese has an atomic number of 25 that gives the electronic configuration as [Ar] 3d54s2 ,where we see that the maximum number of unpaired electrons is found in manganese atom; so, it can show a maximum oxidation state upto +7.
2) Copper is the transition metal of 3d series that exhibits positive E0 (M2+/M). The value of E0(M2+/M) for copper is (+0.34). This happens because the E0 (M2+/M) value of a metal depends on the energy changes involved in the following:
(i) Sublimation energy: The energy required for converting one mole of an atom from the solid state to the gaseous state.
M(s)--> M(g) 
sH (Sublimation energy)
(ii) Ionisation energy: The energy required to take out electrons from one mole of atom in the isolated gaseous state.
M(g)--> M2+(g) 
iH (Ionisation energy)
(iii) Hydration energy: The energy released when one mole of ions are hydrated.
M2+(g)--> M2+(aq) 
hydH (Hydration energy)
Since, copper has a high energy of atomization and low hydration energy, the E0(M2+/M) value for copper is positive.
3) Out of Cr3+ and Mn3+, Mn3+ is a stronger oxidising agent because it has 4 electrons in its valence shell and when it gains one electron to form Mn2+, it results in the half-filled (d5) configuration that has extra stability.
4) Europium (Eu) is well-known to exhibit +2 oxidation state due to its half filled f orbital in +2 oxidation state.
5) MnO4- + 8H+ + 5e- ---> Mn2+ + 4 H2O
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