What are the oxidation number of the underlined elements in each of the following and how do you rationalise your results ?
(a) KI3
(b) H2S4O6
(c) Fe3O4
(d) CH3CH2OH
(e) CH3COOH
(a) KI3
Let assume oxidation number of l is x.
In KI3, the oxidation number (O.N.) of K is +1.
1(+1) + 3(x) = 0
⇒ +1 +3x = 0
⇒ 3x = -1
⇒ x = -1/3
Hence, the average oxidation number of I is - 1/3
However, O.N. cannot be fractional. Therefore, we will have to consider the structure of KI3 to find the oxidation states. In a KI3 molecule, an atom of iodine forms a coordinate covalent bond with an iodine molecule.
Hence, in a KI3 molecule, the O.N. of the two I atoms forming the I2 molecule is 0, whereas the O.N. of the I atom forming the coordinate bond is –1.
(b) H2S4O6
Let assume oxidation number of S is x.
The oxidation number (O.N.) of H is +1.
The oxidation number (O.N.) of O is -2.
2(+1) + 4(x) + 6(-2) = 0
⇒ 2 + 4x - 12 = 0
⇒ 4x -10 = 0
⇒ 4x = +10
⇒ x = +10/4
However, O.N. cannot be fractional. Hence, S must be present in different oxidation states in the molecule.
The O.N. of two of the four S atoms is +5 and the O.N. of the other two S atoms is 0.
(c) Fe3O4
Let assume oxidation number of Fe is x.
The oxidation number (O.N.) of O is -2.
3(x) + 4(-2) = 0
⇒ 3x - 8 = 0
⇒ 3x = 8
⇒ x = 8/3
However, O.N. cannot be fractional.
Here, one of the three Fe atoms exhibits the O.N. of +2 and the other two Fe atoms exhibit the O.N. of +3.
(d) CH3CH2OH
Let assume oxidation number of C is x.
The oxidation number (O.N.) of O is -2.
The oxidation number (O.N.) of H is +1.
x + 3(+1) + x + 2(+1) + 1(-2) + 1(+1) = 0
⇒ x +3 + x +2 - 2 + 1 = 0
⇒ 2x + 4 = 0
⇒ 2x = -4
⇒ x = -2
Hence, the oxidation number of C is -2.
(e) CH3COOH
Let assume oxidation number of C is x.
The oxidation number (O.N.) of O is -2.
The oxidation number (O.N.) of H is +1.
x + 3(+1) + x + (-2) + (-2) + 1(+1) = 0
⇒ 2x + 3 - 2 - 2 + 1 = 0
⇒ 2x + 0 = 0
⇒ x = 0
However, 0 is average O.N. of C.
The two carbon atoms present in this molecule are present in different environments. Hence, they cannot have the same oxidation number. Thus, C exhibits the oxidation states of +2 and –2 in CH3COOH.
Popular Questions of Class 11 Chemistry
- Q:-
Calculate the amount of carbon dioxide that could be produced when
(i) 1 mole of carbon is burnt in air.
(ii) 1 mole of carbon is burnt in 16 g of dioxygen.
(iii) 2 moles of carbon are burnt in 16 g of dioxygen.
- Q:-
The mass of an electron is 9.1 × 10–31 kg. If its K.E. is 3.0 × 10–25 J, calculate its wavelength.
- Q:-
Calculate the wavelength of an electron moving with a velocity of 2.05 × 107 ms–1.
- Q:-
Balance the following redox reactions by ion – electron method :
(a) MnO4 – (aq) + I – (aq) → MnO2 (s) + I2(s) (in basic medium)
(b) MnO4 – (aq) + SO2 (g) → Mn2+ (aq) + HSO4– (aq) (in acidic solution)
(c) H2O2 (aq) + Fe 2+ (aq) → Fe3+ (aq) + H2O (l) (in acidic solution)
(d) Cr2O7 2– + SO2(g) → Cr3+ (aq) + SO42– (aq) (in acidic solution)
- Q:-
In a process, 701 J of heat is absorbed by a system and 394 J ofwork is done by the system. What is the change in internal energy for the process?
- Q:-
What will be the minimum pressure required to compress 500 dm3 of air at 1 bar to 200 dm3 at 30°C?
- Q:-
In a reaction A + B2 → AB2 Identify the limiting reagent, if any, in the following reaction mixtures.
(i) 300 atoms of A + 200 molecules of B
(ii) 2 mol A + 3 mol B
(iii) 100 atoms of A + 100 molecules of B
(iv) 5 mol A + 2.5 mol B
(v) 2.5 mol A + 5 mol B
- Q:-
At 0°C, the density of a certain oxide of a gas at 2 bar is same as that of dinitrogen at 5 bar. What is the molecular mass of the oxide?
- Q:-
Which one of the following will have largest number of atoms?
(i) 1 g Au (s)
(ii) 1 g Na (s)
(iii) 1 g Li (s)
(iv) 1 g of Cl2(g)
- Q:-
Density of a gas is found to be 5.46 g/dm3 at 27 °C at 2 bar pressure. What will be its density at STP?
Recently Viewed Questions of Class 11 Chemistry
- Q:-
Define environmental chemistry.
- Q:-
Draw the cis and trans structures of hex-2-ene. Which isomer will have higher b.p. and why?
- Q:-
Starting with sodium chloride how would you proceed to prepare
(i) sodium metal (ii) sodium hydroxide (iii) sodium peroxide (iv) sodium carbonate?
- Q:-
How will you convert benzene into
(i) p - nitrobromobenzene
(ii) m - nitrochlorobenzene
(iii) p - nitrotoluene
(iv) acetophenone?
- Q:-
Explain the formation of a chemical bond.
- Q:-
For the reaction
2 A(g) + B(g) → 2D(g)
ΔU0 = –10.5 kJ and ΔS0 = –44.1 JK–1.
Calculate ΔG0 for the reaction, and predict whether the reaction may occur spontaneously.
- Q:-
The ionization constant of acetic acid is 1.74 x 10-5. Calculate the degree of dissociation of acetic acid in its 0.05 M solution. Calculate the concentration of acetate ion in the solution and its pH.
- Q:-
What happens when
(i) magnesium is burnt in air
(ii) quick lime is heated with silica
(iii) chlorine reacts with slaked lime
(iv) calcium nitrate is heated ?
- Q:-
Thermodynamically the most stable form of carbon is
(a) diamond (b) graphite (c) fullerenes (d) coal
- Q:-
On the basis of quantum numbers, justify that the sixth period of the periodic table should have 32 elements.
1 Comment(s) on this Question
Thanks for your NCERT solution
- NCERT Chapter