SpA Test (14-10-2018) - Chemistry MCQ

-d[N₂O₅]/dt = +2d[NO₂]/dt = 1/2d[O₂]/dt

rate of formation of NO₂ = (rate of disappearence of N₂O₅)/2

rate of formation of NO₂ = 6.25x10^-3/2 = 3.125x10³

rate of formation of O₂=rate of disappearence of N₂O₅)²

rate of formation of O₂

= 6.25*10^-3x2

=1.25x10^-2

The logarithmic form of Arrhenius equation is

logk = log A−Ea 2.303 RT

Given, log k = 6 − 2000 T

Comparing the above two equations :

logA=6⇒A=10⁶

and Ea 2.303 R=2000

⇒Ea=2000×2.303×8.314J

=38.3 kJmol−1

Thus the activation energy is 38.3 kJmol−1

The most abundant and widely studied nitrogenase group is the Mo-dependent enzyme, which has an active site metallo-cofactor called FeMo-cofactor 

The primary valencies in (i) CoCl₃.6NH₃, (ii) CoCl₃.5NH₃, (iii) CoCl₃.4NH₃. If the number of co-ordinated NH₃ molecules in i, ii and iii respectively are 6, 5, 4,(i), (ii) and (iii) are 3, 2 and 1 respectively.

(i) CoCl₃.6NH₃ in this complex Co is co-ordinated with six NH₃ molecules, which means the primary valency of Co is 3. complex is [Co(NH₃)₆]Cl₃

(ii) CoCl₃.5NH₃ in this complex Co is co-ordinated with five NH₃ molecules, which means the primary valency of Co is 2.complex is [Co(NH₃)₅]Cl₂

(iii) CoCl₃.4NH₃ in this complex Co is co-ordinated with four NH₃ molecules, which means the primary valency of Co is 1.complex is [Co(NH₃)₄]Cl

This reaction involves the reductive homo-coupling of a carbonyl compound to produce a symmetrically substituted 1,2-diol. The first step is single electron transfer of the carbonyl bond, which generates radical ion intermediates that couple via carbon-carbon bond formation to give a 1,2-diol. The example depicted above shows the preparation of pinacol itself.

Pinacol and other highly substituted 1,2-diols tend to undergo dehydration with rearrangement under acid-catalysis.

Out of all four statements option D is not correct since an order of reaction can be 1, 2, 3 ... and even fractional also.

Also, an order can be determined experimentally and if is not affected by the stoichiometric coefficient of the reactants.

Beta keto acids readily undergo thermal decarboxylation. The compound that undergoes decarboxylation most readily under mild condition is 2-oxocyclohexanecarboxylic acid (option B) as it is a beta keto acid. The product obtained is cyclohexanone.
 

The complex [Co(NH₃​)₃​Cl₃​] does not have optical isomers due to presence of an element of symmetry. However, it exists in two geometrical isomers which are cis and trans or fac and mer isomers.

(a) In [Sc(H₂​O)(NH₃​)₃​]³⁺ Sc is present in Sc³⁺=[Ar]3d⁰,4s⁰

Since in this complex excitation of the electron is not possible, it will not absorb visible light.

(b) [Ti(en)_2​(NH_3​)₂​]⁴⁺, Ti is present as Ti⁴⁺

 Ti₄₊=[Ar]3d⁰,4s⁰

Hence it will not absorb visible light

(c) In [Cr(NH_3​)₆​]³⁺ Cr is present as Cr³⁺

Cr =[Ar]3d³,4s⁰ 

Since this complex has three unpaired electrons excitation of electrons is possible and thus, it is expected that this complex will absorb visible light.

(d) In [Zn(NH₃​)₆​]²⁺ Zn is present as Zn²⁺

Zn²⁺=[Ar]3d¹⁰,4s⁰

Hence , this complex will not absorb visible light.

The correct option is C.

[Fe(CNS)₆​]³⁻→[FeF₆​]³⁻

CNS is  a strong ligand while  F is a weak ligand . Outer orbital configuration from inner orbital is achieved. hence it causes more spin of electrons. Hence it results in increased magnetic moment. 

Higher the oxidation state of the metal, greater the crystal field splitting energy . In options (a), (b) and (d), Co is present in +2 oxidation state and in (c ) it is present in +3 oxidation state and hence has a higher value of CFSE.