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Coordination Compounds — Chemistry STD 12 Science — Question

Gujarat BoardEnglish MediumSTD 12 ScienceChemistryCoordination Compounds4 Marks
Question
Read the passage given below and answer the following questions: For understanding the structure and bonding in transition metal complexes, the magnetic properties are very helpful. Low spin complexes are generally diamagnetic because of pairing of electrons, whereas high spin complexes are usually paramagnetic because of presence of unpaired electrons. Larger the number of unpaired electrons, stronger will be the paramagnetism. However magnetic behaviour of a complex can be confirmed from magnetic moment measurement. Magnetic moment $\mu=\sqrt{\text{n(n+2)}}\text{B.M.}$ where n = number of unpaired electrons. Greater the number of unpaired electrons, more will be the magnetic moment. In these questions (Q. No. i-iv), a statement of assertion followed by a statement ofreason is given. Choose the correct answer out of the following choices.
  1. Assertion and reason both are correct statements and reason is correct explanation for assertion.
  2. Assertion and reason both are correct statements but reason is not correct explanation for assertion.
  3. Assertion is correct statement but reason is wrong statement.
  4. Assertion is wrong statement but reason is correct statement.
The following questions are multiple choice questions. Choose the most appropriate answer:
  1. Assertion: Both $[Cr(H_2O)_6]^{2+}$ and $[Fe(H_2O)_6]^{2+}$ have same magnetic moment.
Reason: Number of unpaired electrons in $Cr^{2+}$ and $Fe^{2+}$ are same.
  1. Assertion: $[Fe(H_2O)_5NO]SO_4$ is paramagnetic.
Reason: The Fe in $[Fe(H_2O)_5NO]SO_4$ has three unpaired electrons.
  1. Assertion: $[Co(en)_3]^{3+}$ is paramagnetic.
Reason: It is an inner orbital complex.
  1. Assertion: $[Ni(CO)_4]$ is diamagnetic and tetrahedral in shape.
Reason: $[Ni(CO)_4]$ contains no unpaired electrons and involves $dsp^2$ hybridisation.
  1. Assertion: $[Ni(CN)_4]^{2-}$ is diamagnetic complex.
Reason: It involves $dsp^2$ hybridisation and there is no unpaired electron.
✓

Answer

  1. (a) Assertion and reason both are correct statements and reason is correct explanation for assertion.
Explanation:
Spinonlymagneticmoment, $\mu=\sqrt{\text{n(n+2)}}$ where $n =$ number of unpaired electrons.
As the number of unpaired electrons in $Cr^{2+}[(Ar)3d^{4]}$ and $Fe^{2+}[(Ar)3d^6]$ are same, hence $[Cr(H_2O)_6]^{2+}$ and $[Fe(H_2O)_6]^{2+}$ will have same magnetic moment.
  1. (a) Assertion and reason both are correct statements and reason is correct explanation for assertion.
Explanation:
$Fe^+: [Ar)3d^74s^0$
When the weak field ligand $H_2O$ and strong field ligand $NO^+$ attack, the configuration changes as follows: $Fe^+: [Ar)3d^74s^0$​​​​​​​

$\therefore Fe^{2+}$ has $3$ unpaired electrons.
  1. (d) Assertion is wrong statement but reason is correct statement.
Explanation:

In presence of strong ethylenediamine ligand the electrons get paired.

Thus inner orbital complex with no unpaired electrons.
  1. (c) Assertion is correct statement but reason is wrong statement.
Explanation:
$[Ni(CO)_4]$ contains $Ni(O).$​​​​​​​

$CO$ is strong ligand thus,
  1. (a) Assertion and reason both are correct statements and reason is correct explanation for assertion.

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Read the passage given below and answer the following questions: Aniline activates the benzene ring by increasing electron density at ortho- and para-positions. Hence, it is o-, p-directing. -NH2 group strongly activates the ring therefore it is difficult to stop the reaction at monosubstitution stage. Among electrophilic substitution reaction, direct nitration of aniline is not done to get o- and p-nitroaniline because lone pair of electrons present at nitrogen atom will accept proton from nitrating mixture to give anilinium ion which is meta-directing. Aniline with $NaNO_2$ and HCI forms benzene diazonium chloride at very low temperature. Aromatic amines react with nitrous acid to form a yellow oily liquid known as N-nitrosoamines. A statement of assertion followed by a statement of reason is given. Choose the correct answer out of the following choices.
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