Ncert Solutions Chemistry Class 12th

Bonding in coordination compounds in terms of Werner's postulates is explained as:

(a) Metals can show two types of valencies which are Primary valency and Secondary

1. Primary Valency: Primary Valency shows Oxidation Primary valencies are ionizable.

2. Secondary Valency: Secondary Valency shows coordination These are non-ionizable.

(b) Both Primary and secondary valency of the metal are to be satisfied which is done by negative ions in case of primary valency and negative or neutral species in case of secondary

(c) Metals have a fixed number of secondary valencies/ Coordination number around the central atom, these secondary valencies are placed in such a way which leads to a specific geometry of the coordination

14.31

In the helical structure of DNA, the two strands are held together by hydrogen bonds between specific pairs of bases.

Cytosine from hydrogen bond with guanine, while adenine forms hydrogen bond with thymine. As a result, the two strands are complementary to each other.

DNA consists of two strands of nucleic acid chains coiled around each other in the form of a double helix. The base of one strand of DNA is paired with bases on other strand by means of hydrogen bonding.

This hydrogen bonding is very specific as the bases can only base pair in a complementary manner.

Adenine pairs with only thymine via 2 hydrogen bonds and guanine pairs with cytosine through 3 hydrogen bonds. 

Thus, the two strands of DNA are complementary to each other in the sense that the sequence of bases in one strand automatically determines that of the other. So the DNA stands cannot be identical, but they are complementary to each other.

14.29

Nucleic acids are Biomolecules which are found in the nuclei of all living cells, inform of nucleoproteins or chromosomes (proteins containing nucleic acids as the prosthetic group). Nucleic acids are of two types: – deoxyribonucleic acid (DNA) and ribonucleic acid (RNA). Nucleic acids are also known as Polynucleotide as they are long- chain polymers of nucleotides.

The two important functions of nucleic acids are listed below:-

(i) DNA which is responsible for the transference of hereditary effects from one generation to another, which is due to their property of replication during cell division as a result of which two identical DNA strands are transferred to the daughter

(ii) Nucleic acids (both DNA and RNA) are responsible for synthesis of all proteins needed for the growth and maintenance of our body. Actually, the proteins are synthesised by various RNA molecules in the cell but the message for the synthesis of a particular protein is given by DNA molecules

In [Fe (H₂O)₆]³⁺

Electronic configuration of Fe is: [Ar]3d⁶4s²

[Ar] = 1s²2s²2p⁶3s²3p⁶

Electronic configuration of Fe⁺³ = [Ar]3d⁵

Outer electronic configuration of Fe⁺³ = 3d⁵

Overall charge balance:

X + 6 (0) = 3

X = + 3

In [Fe (CN)₆]^3-

Overall charge balance:

X + 6 (-1) = -3

X = + 3

In both the compounds Fe is in + 3 oxidation state.

In case of [Fe (H₂O)₆]³⁺

H₂O is weak field ligand so it does not pair the unpaired electron. Total no. of the unpaired electron, n =5, Spin only magnetic moment is given by:

μ = [n (n + 2)]^1/2

μ = [5*7]^1/2

μ = 5.916BM

In case of [Fe (CN)₆]^3-

CN^- is a strong field ligand so it pairs up the electron.

Total no. of unpaired electrons = 1

Spin only magnetic moment is given by:

μ = [n (n + 2)]^1/2

μ = [1*3]^1/2

μ = 1.732BM

as we can see spin only magnetic moment of [Fe (H₂O)₆]³⁺ is more than [Fe (CN)₆]^3- .

so, [Fe (H₂O)₆]³⁺ is strongly paramagnetic whereas [Fe (CN)₆]³ weakly paramagnetic.

Fe in ground state

Fe in + 3 oxidation state

Electrons from 5 CN^- ligands

In [Ni (Cl)₄]^2- ion, Cl^- is a weak field ligand so it will not pair the unpaired electrons of Ni⁺² ion. Electronic configuration of Ni is: [Ar]3d⁸4s² where [Ar] = 1s²2s²2p⁶3s²3p⁶

Electronic configuration of Ni⁺² = [Ar]3d⁸ Outer electronic configuration of Ni⁺² = 3d⁸ Overall charge balance:

X + 4 (-1) = -2 X = + 2.

Therefore it undergoes sp³ hybridization. So it will have tetrahedral geometry.

Since there are 2 unpaired electrons in the d orbital so it is a paramagnetic compound. In [Ni (Co)₄]:

Overall charge is neutral and oxidation state of Ni can be calculated as:

X + 4 (0) = 0

x = 0

Ni is in zero oxidation state.

Co is a strong field ligand it causes pairing of the 4 unpaired electrons in d orbital. Also, it causes the 4s electrons to shift to the 3d orbital, thereby undergoes sp³ hybridisation forming tetrahedral geometry. Since it has no unpaired electron, therefore it is diamagnetic compound.