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Questions and Answers Inorganic Chemistry

Problems on Inorganic Chemistry appear really as problems to the most of students studying in different Schools, Colleges and Different universities. To Overcome this Problems to achieve a good performance in Examinations i will discuss some of these problems Topic Wise. This page is Updated Regularly so Keep on Touch With this Page.


How can convert 1 Debye to Coulomb Meter.

The dipole moment in CGS system is, µ = 4.8 × 10⁻¹⁰ × 10⁻⁸ esu cm = 4.8 D 
In SI system, 1.6 ×10⁻¹⁹ × 10⁻¹⁰ coulomb × metre 
= 1.6 × 10⁻³⁰ C×m 
Thus, 4.8 Debye = 1.6 ×10⁻³⁰ C×m 
or, 1 Debye = (1.6 × 10⁻³⁰)/4.8 C×m 
or, 1 Debye = 3.336 × 10⁻³⁰ C×m

Find out the Unit and Dimension of Dipole Moments.

Unit of µ = Unit of Charge × Unit of Length. 
Thus, the unit of µ = esu × cm in CGS system. 
But from the Coulomb’s Low, 
F = q1q2/D r² 
Thus, (esu)² = dyne × cm²
= gm cm sec⁻² × cm² 
Hence, esu = gm1/2 sec-1 cm3/2 
Hence the dimension of µ = M1/2 T-1 L5/2

The displacement of HCl is 1.03 Debye and its bond length is 1.27 A. calculate the (a) charge on the constituent atom and (b) the % of the ionic Character of HCl.

Given, μobs = 1.03 Debye = 1.03 × 10⁻¹⁸ esu cm 
and length ℓ = 1.27 × 10 ⁻⁸cm. 
(a). Hence the charge on the constituent atom(q), = μobs/ℓ 
= (1.03 × 10⁻¹⁸ )/( 1.27 × 10⁻⁸) 
= 0.8 × 10⁻¹⁰ esu 
(b) The % of the ionic Character of the molecule, (μobsionic ) ×100 
=(1.03 × 10⁻¹⁸)/(4.8 ×10⁻¹⁰×1.27 × 10⁻⁸) ×100 
= 16.89%

The Difference between electronegativity of Carbon and Oxygen Is large but the dipole moments of carbon monoxide is very low - Why?

See The topic Dipole Moments.

The bond angle in H₂S is 97° and dipole moment = 0.95 D . Find the bond moment of the S - H link. ( Given, Cos97° = -0.122)

We have, μ = 0.95 D and θ = 97° . 
From the equation, 
μ² = 2 m² (1+ cosθ ) 
Putting the value we have, 
(0.95)² = 2 m² (1+ cos97° ) 
here m = mS - H 
 or, 0.9025 = 2 m² (1-0.122) 
or, m² = 0.9025/ (2 × 0.878) 
 or, m² = 0.5139 
or, m = 0.72 
Thus the bond moment of the S - H link is 0.72 D

Calculate the ionization potential of hydrogen atom in eV.

We know that, the energy corresponding to the transition from n = ∞ to n = 1 gives the ionization potential of the hydrogen atom.
Thus the Ionization Potential of the Hydrogen atom, 
= (2π²me⁴/h²) {(1/1²) - 0}
EH = 2.179 × 10⁻¹¹ erg 
= 2.179 × 10⁻¹⁸ Joule 
= (2.179 × 10⁻¹⁸)/(1.6 × 10⁻¹⁹) eV 
= 13.6 eV

Calculate the second ionization potential of helium 
(given ionization potential of hydrogen = 13.6 eV)

The ground state electronic configuration of helium is 1S². The second ionization potential means removal of the second electron from the 1S orbital against the nuclear charge of +2.
So we have: Ionization Potential 
= (2π²me⁴/){(1/n₁²) - (1/n₂²)
= Z² × EH
∴ Second Ionization Potential of Helium = 2² × 13.6 = 54.4 eV

In first transition series electron filling up processes begins in the 3d level below a filled 4S² level. During ionization process will a 4S electron or a 3d electron be lost first ? Explain with reference to Chromium.

Electronic Configuration of Chromium (Cr) : 
1S² 2S² 2P⁶ 3S² 3p⁶ 3d⁵ 4S¹
Screening constant (σ) for 4S electron is : 
σ = (2 × 1.0) + (8 × 1.0) + (8 × 0.85) + (5 × 0.85)
= 21.05.
∴Effective nuclear charge = (24 - 21.05) 
= 2.95.
Screening constant (σ) for 3d electron is : 
σ = (2 × 1.0) + (8 × 1.0) + (8 × 1) + (4 × 0.35)
= 19.4.
∴Effective nuclear charge = (24 - 19.4) 
= 4.60.

Arrange the following with the increasing order of Ionization Potentials 
Li, Be, B, C, N, O, F, Ne.

LiBBeCONFNe

Calculate the effective nuclear charge of the hydrogen atom.

Hydrogen atom has a single 1S valence electron. There is no other electron to screen it from the nuclear charge of single proton.
Thus, σ = 0 and Z* = 1.0 -0 = 1.0
Thus hydrogen electron sees the full nuclear charge of the nucleus, that is the electron is totally exposed to the proton.

Find out the Screening Constant of the 4S and 3d electron of Chromium Atom.

Chromium has atomic number 24 and the electronic configuration according to the Slater's Rule is :
(1S)² (2S, 2P)⁸ (3S, 3P)⁸ (3d)⁵ (4S)¹
∴ Screening Constant (σ) for the 4S electron is :
σ =(2 ×1.0) + (8×1.0) + (8×1.0) + (3×0.85) (0×0.35) 
21.05.
And the Screening Constant (σ) for the 3d electron is :
σ =  (2 ×1.0) + (8×1.0) + (8×1.0) + (4×0.35) 
= 19.4.
Estimate the screening constant for the outermost 4S electron of Vanadium.
Vanadium has atomic number 23 and the electronic configuration according to the Slater's Rule is :
(1S)² (2S, 2P)⁸ (3S, 3P)⁸ (3d)³ (4S)² 
We have consider only one electron of the two 4S electrons.
∴Screening Constant (σ
= (2 ×1.0) + (8×1.0) + (8×0.85) +(3×0.85) (1×0.35) 
= 19.7.


Calculate the electron affinity of chlorine from the Born -  Haber cycle, given the following date : lattice energy = - 774 kJ mol⁻¹ , Ionization Potential of Na = 495 kJ mol⁻¹, heat of sublimation of Na = 108 kJ mol⁻¹, energy for bond dissociation of chlorine (Cl₂) = 240 kJ mol⁻¹ and heat of formation of NaCl = 410 kJ mol⁻¹.

Born - Haber Cycle for formation of NaCl (S) is:
How to determine Electron Affinity
Born - Haber Cycle Applied to NaCl
From the above Born - Haber cycle we can written as:

- UNaCl - INa + ECl - SNa - 1/2DCl - ΔHf = 0
or,  ECl = UNaCl + INa + SNa + 1/2DCl + ΔHf 
∴ ECl = -774 + 495 + 108 + 120 + 410
= 359 kJ mol⁻¹


Account for the large decrees in electron affinity from lithium to beryllium despite the increase in nuclear charge.

Atomic number and the electronic distribution of lithium and beryllium are:
Li : 3 : 1S² 2S¹
Be : 4 : 1S² 2S²
Lithium has an incompletely filled 2S sub-shell while beryllium has the sub shell filled. Thus lithium can receive an electron in its 2S sub-shell but for beryllium a still higher energy 2P level has to be made of. A filled shell or sub-shell leads to some extra stability. Hence beryllium resists an extra electron more than does lithium.

Why electron affinity of Nitrogen is - 0.10 eV while that of Phosphorus is + 0.70 eV ?

Due to smaller size of Nitrogen atom when extra electron is added to the stable half - filled 2P orbital some amount of energy is required and hence electron affinity of nitrogen is negative. 
On the other hand, due to bigger size of P atom in compare to nitrogen less amount of energy released when the extra electron is added to the stable half - filled 3P orbitals and thus electron affinity of Phosphorus is expressed with positive sign.
(c) Electron Affinity data on noble gases are not available.

Oxidation number of P in Ba(H₂PO₂)₂ is - (a)+3, (b)+2, (c) +1, (d) -1.

(c) +1
Oxidation number of Ba is +2, oxidation number of hydrogen is +1 and oxidation number of oxygen is -2.
Let the oxidation number of P is x.
∴ (+2)+2{2(+1)+x+2(-2)} = 0
or, 2x-2=0; 
or, x=+1 

Calculate the oxidation number of Iron in [Fe(H₂O)₅(NO)⁺]SO₄.

H₂O is neutral thus the oxidation number is zero, oxidation number of (NO)⁺ is +1 and the oxidation number of SO₄ is -2.
Let the oxidation number of Fe in [Fe(H₂O)₅(NO)⁺]⁺² is x.
∴ x + 0 + (+1) + (-2) = 0 
or, x-1 = 0
or, x = +1 
Thus, the oxidation number of Fe in [Fe(H₂O)₅(NO)⁺]⁺² is +1.

Calculate the oxidation number of the element marked with line in the following compounds, (i) K₂CrO₄, (ii) HOCl, (iii) BaO₂, (iv) ClNO, (v) NaNH₂, (vi) NaN₃, (vii) CH₂Cl₂, (viii) Ca(OCl)Cl, (ix) Ba(MnO₄)₂ (x) CaH₂.

Compound
Element Oxidation Number
 K2CrO4
Cr +6
HOCl
Cl +1
 BaO2
Ba +2
ClNO
N +3
 NaNH2
N - 3
 NaN3
N - (1/3)
 CH2Cl2
C 0
Ca(OCl)Cl
Cl +1
 Ba(MnO4)2
Mn +7
 CaH2
H -1

What is the Oxidation state of chromium in Cr2O5?

Due to peroxy linkage oxidation state of Cr in Cr2O5 is +6.

Why sulphur dioxide has properties of Oxidation and reduction?

This can be explain by the oxidation state of sulphur. The oxidation numbers of sulphur in the compounds H₂S, SO₂, and SO₃ are -2, +4 and +6 respectively. Thus the highest oxidation state of sulphur is +6 and lowest is -2. The oxidation state of free sulphur element is 0. In SO₂, the oxidation state of sulphur is +4, this oxidation state is middle of 0 and +6.
Thus, the oxidation state can increases from +4 to +6 and decreases from +4 to 0.

Express by ion electron method the reduction of permagnate to manganous stat by hydrogen peroxide in acid medium.

This Reaction occurs in acid medium and the partial equation is:
MnO₄⁻ + 8H⁺ + 5e  Mn⁺² + 4H₂O (Reduction of Oxidant)
In acid medium H₂O₂ will give O₂ and the partial equation being:
H₂O₂  2H⁺ + O₂ +2e 
(Oxidation of Reductant)
First equation is multiplying by 2 and the second is 5 to have electron balanced. 
We have,
2MnO₄⁻ + 16H⁺ + 10e  2Mn⁺² + 8H₂O
5H₂O₂ 10H⁺ + 5O₂ +10e

2MnO₄⁻+5H₂O₂+6H⁺2Mn⁺²+8H₂O+5O₂

Express by ion - electron method the reduction of nitrate ion to 
ammonia by aluminium in aqueous NaOH.

In alkaline medium we use H₂O and OH⁻ ion according to convenience. The partial equation with charge balance is:
NO₃⁻ + 6H₂O + 8e NH₃ + 9OH⁻
Metallic aluminium will go over to aluminate ion, the partial equation being:
Al + 4OH⁻ AlO₂⁻ + 2H₂O +3e
Multiplying by right factors for electron balance we have the balanced equation:
3NO₃⁻ + 18H₂O + 24e 3NH₃ + 27OH⁻
8Al + 32OH⁻ 8AlO₂⁻ + 16H₂O +24e

3NO₃⁻+8Al+2H₂O+5OH⁻3NH₃+8AlO₂⁻

Use Oxidation Number method to balance the reaction of iodide ion 
and iodate ion in acid medium to liberate iodine.

The reaction represented as, I⁻ + IO₃⁻ I₂
Representation of the above equation with oxidation number of iodine,
I⁻(-1) + IO₃⁻(+5) I₂(0)
Since I⁻ (-1) oxidation number of iodide increases by 1 and IO₃⁻(+5) oxidation number decreases by 5.
Putting the right factors the decrease and increase in oxidation number balanced:
5I⁻ + IO₃⁻ 3I₂
Since the medium is acidic and the charges are unequal on two sides of the above expression we put Six H⁺ and write three H₂O to balanced the equation:
I⁻ + IO₃⁻ + 6H⁺ I₂ + 3H₂O

Use oxidation number method to balance the reaction between 
Sulphurus acid and dichromate in acidic medium.

The reaction represented as,
SO₃⁻² + Cr₂O₇⁻² SO₄⁻² + 2Cr⁺³
Oxidation of two Cr decreases by 2 × (+3) = 6 and oxidation number of S increases by 2.
Equalizing the above equation increase and decrees in oxidation number,
We have, 3SO₃⁻² + Cr₂O₇⁻²  3SO₄⁻² + 2Cr⁺³
Because of the medium is acidic and the ionic charges are not equal on the two sides, eight H⁺ ions are added to the Left hand side. 
3SO₃⁻² + Cr₂O₇⁻² + 8H⁺  3SO₄⁻² + 2Cr⁺³
Since there are eight hydrogen ion on the left and none on the right, four H₂O added to make atom balance.
Thus the final equation is:
3SO₃⁻²+Cr₂O₇⁻²+8H⁺3SO₄⁻²+2Cr⁺³+4H₂O