Chemistry NCERT Exemplar Solutions Class 12th Chapter Eight
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4 months agoContributor-Level 10
17. Magnetic moment of an electron/dipole moment is caused by its intrinsic properties of spin and electric charge. It depends upon the number of unpaired electrons in its valence shell. The more the number of unpaired electrons, the greater will be the value of magnetic moment.
Cr3+ = [Ar] 3d3 = 3 unpaired electrons
Co2+ = [Ar] 3d7 = 3 unpaired electrons
But as both the ions have the same no. of unpaired electrons, there's one other factor called orbital contribution which also influences the magnetic moment. As, the three unpaired electronic configuration is sy
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4 months agoContributor-Level 10
16. Fluorine - 1s22s22p5
Oxygen - 1s2 2s2 2p6 3s2 3p6
As we can infer from the electronic configuration, fluorine only has one unpaired electron in its 2p-orbital which can be involved in formation of only one bond and fluorine lacks d-orbital.
While oxygen has d-orbitals in its configuration which allow the oxygen to form multiple bonds. Therefore, oxygen has greater stability to stabilise its oxidation states than fluorine.
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4 months agoContributor-Level 10
15. The reactions are explained as:
MnO2 + 4HCl → MnCl2 + Cl2 + 2H2O
(A) (B)
3Cl2 + 2NH3 → NCl3 + 3HCl
(excess) (C)
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4 months agoContributor-Level 10
14. Higher enthalpy of hydration provides extra stability to Cu2+ oxidation state than +1 oxidation state.
Enthalpy of hydration is described as the amount of energy released on dilution of one mole of gaseous ions.
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4 months agoContributor-Level 10
13. 2Cu2+ + 4I- → Cu2I2 + I2
When Cu2+ reacts with potassium iodide white precipitate of Cu2I2 is formed.
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4 months agoContributor-Level 10
12. Transition elements have the ability to involve their d-electrons along with their s-electrons in the process of bond formation. This results in formation of strong metal-metal bonds which makes their melting point high.
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4 months agoContributor-Level 10
11. Cr (24)= [Ar]3d54s2
Zn (30) = [Ar] 3d104s2
The stability of orbitals according to the electrons filled is in order:
Fully filled > half-filled > partially filled
As 3d10 is completely filled orbital of Zn is more stable than the 3d5 half-filled orbital of Cr . It is comparatively easy to remove electron from 3d5 than from 3d10.
Therefore, the first ionization enthalpy of Cr is lower than that of Zn.
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4 months agoContributor-Level 10
10. Mn has half-filled 3d5 electrons and Zn has fully-filled 3d10 electrons which give them extra stability and they both resist to lose electrons and get reduced.
The E? value also depends on the hydration enthalpy. More negative is the enthalpy of hydration, high is the E? value. This is the reason behind Mn, Ni and Zn are having higher E? value than expected
New answer posted
4 months agoContributor-Level 10
9. Copper lies below hydrogen in electrochemical series which means it has positive standard reduction potential i.e. + 0.34 V. and hence cannot liberate hydrogen from acids.
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4 months agoContributor-Level 10
8. KMnO4 
K2MnO4 + MnO2 + O2
(A) (B) (C)
MnO2 + KOH → 2K2MnO4 + 2H2O
MnO2 + 4NaCl + 4H2SO4→ MnCl2 + 2NaHSO4+2H2O + Cl2
(D)
(A) = KMnO4
(B) = K2MnO4
(C) = MnO2
(D) = MnCl2
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