CSIR_UGC_Net_Chemistry-June-2019

 

Question: The role of H₃PO₄ in the estimation of Fe(II) with K₂Cr₂O₇ using diphenylamine sulphonate as indicator is to

a)                  Avoid aerial oxidation of Fe(II)

b)                  Reduce the electrode potential of Fe³⁺ → Fe²⁺

c)                  Stabilizer the indicator

d)                 Stabilize K₂Cr₂O₇

Answer : (b) Reduce the electrode potential of Fe³⁺ → Fe²⁺

Explanation

• For the titration of Fe²⁺ with K₂Cr₂O₇ different indicators like diphenylamine, diphenylbenzidine and diphenylamine sulfonate may be used. All these indicators give green to violet colour. To reduce the electrode potential for the Fe³⁺ → Fe²⁺ reaction phosphoric acid is added and stabilising the ferric ion.
• The role of H₃PO₄ in the estimation of Fe(II) with K₂Cr₂O₇ using diphenylamine sulphonate as indicator is to Reduce the electrode potential of Fe³⁺ →  Fe²⁺

 

Question: In neutron activation analysis the radiation commonly detected is

a)                    α - rays

b)                  β - rays

c)                   γ - rays

d)                 X-rays     

Answer : (c)   γ - rays

Explanation

• In neutron activation analysis γ – rays radiation detected.

Question: The number of Ni- Ni bonds in [CpNi(μ-PPh₂)]₂ complex obeying the 18-electron rule is

a)                  0

b)                  1

c)                  2

d)                 3

Answer : (a) 0

Explanation

• No. of Ni-Ni bond = [(18x2)-Total valence electron]/2 = [(18x2)-36]/2 = 0
• The number of Ni- Ni bonds in [CpNi(μ-PPh₂)]₂ complex is zero.

Question: The metal transferred by bacteria and fungi using siderophores/siderochromes is

a)                  Mo

b)                  Cu

c)                  Fe

d)                 Zn

Answer : (c)   Fe

Explanation

• Siderophores usually form a stable, hexadentate, octahedral complex preferentially with Fe³⁺ compared to other naturally occurring abundant metal ions.
• The metal transferred by bacteria and fungi using siderophores/siderochromes is Fe.

Question: Self exchange electron transfer is fastest in

a)                  [Ru(NH₃)₆]^2+/3+

b)                  [Co(NH₃)₆]^2+/3+

c)                  [Cr(H₂O)₆]^2+/3+

d)                 [Fe(H₂O)₆]^2+/3+

Answer : (a)   [Ru(NH₃)₆]^2+/3+

Explanation

• Electron transfer requires orbital overlap and occurs between orbitals of the same symmetry.
• e_g  → e_g transition = large change in bond length - Slow electron transfer
• t_2g → t_2g transition = small change in bond length - Fast electron transfer.
• 2^nd and 3^rd row metals generally faster that 1^st row due to better overlap of 4d and 5d orbitals. (Also due to stronger ligand fields bond length distortions will be smaller).
•  Ligands that have extended π systems e.g. Phen, bipy etc can assist electron transfer.
• Ru belonging from 2^nd row metal so better overlap of 4d orbitals as a result Self exchange electron transfer is fastest in [Ru(NH₃)₆]^2+/3+