1) The most useful ore of aluminum is bauxite, in which Al is present as hydrate

Question

1) The most useful ore of aluminum is bauxite, in which Al is present as hydrated oxides, Al2O3 * xH2O. The number of kilowatt-hours of electricity required to produce 3.00kg of aluminum from electrolysis of compounds from bauxite is _____ when the applied emf is 4.50V.

a)0.0249

b)0.0402

c) 26.8

d)13.4

e)40.2

2)The standard emf for the cell using the overall cell reaction below is +0.48V

Zn(s) + Ni^2+(aq)--------> Zn^2+(aq)+Ni(s)

the emf generated by the cell when [Ni^2+]=0.100M and [Zn^2+]= 2.25M is _____V.

a)0.56

b)0.50

c)0.44

d)0.40

e)0.52

3) How many d electrons are associated with the metal ion in [Cr(NH3)6]^3+?

a)3 b)2 C)1 d)0

4)Which of the following can form both high- and low- spin octahedral complexes?

a) Ru^2+ b)Cr^4+ c)Zr d)Ag+

Explanation / Answer

1. e. 40.23 (Using the standard formula Q = nFE)

2. Using Nernst equation, E = E0 -0.059/n log [red.]/[ox.]

c)0.44 [E= 0.48 V -0.059/2 log 2.25/0.1]

3. Cr at ground state electronic configuration [Ar]3d4 4s2

Hence in the compound, Cr is at (+3) oxidation state which gives electronic configuration of  [Ar]3d3 4s0

So, answer is a)3

4. Ru: [Kr] 4d75s1 so, Ru^2+:  [Kr] 4d6 can form both high and low spin since it contains 6 d electrons i.e. >3 electrons required to respond to electron transfer at higher d energy orbitals under weak field

Cr: [Ar]3d4 4s2 so, Cr^4+ : [Ar]3d2 not enough d electrons, has to be at least 3 to half fill dxy, dyz and dzx

Zr: [Kr] 4d25s2 not enough d electrons, has to be at least 3 to half fill dxy, dyz and dzx

Ag: [Kr] 4d105s1 so, Ag+ : [Kr] 4d10 all d orbitals filled up, so not applicable.

Hence, answer is a) Ru^2+

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