Class 11th

(a) CO₃^2-  (sp²) (b) Diamond (sp³) (c) Graphite (sp²)

1.3 We are given that the percentage of iron by mass is 69.9% and the percentage of oxygen by mass is 30.1%.

Since we have relative moles of both elements, we can calculate the simpler molar ratio of iron to oxygen

= 1.25: 1.88

Divide by the smaller value to both

= 1.25/1.25: 1.88/1.25

= 1: 1.5

= 2: 3

So, now we can write the empirical formula of iron oxide as Fe₂O₃.

Electron deficient compounds are those in which the central atom in their molecule has the tendency to accept one or more electron pairs. They are also known as Lewis acid. BCl₃ and SiCl₄ both are electron deficient species.
Since, in BCl₃, B atom has only six electrons. Therefore, it is an electron deficient compound.
In SiCl₄ the central atom Si has 8 electrons but it can expand its covalency beyond 4 due to the presence of d-orbitals.

Aluminium reacts with acid as well as base. This shows amphoteric nature of aluminium.
2Al (s) + 6HCl (dil.) →2AlCl₃ (aq) + 3H₂ (g)
2Al (s) + 2NaOH (aq) + 6H₂O (l) →2Na+ [Al (OH)₄]^– (aq) + 3H₂ (g)

1.2 Molar mass of Na₂SO₄= (2 x Atomic mass of Sodium) + Atomic mass of Sulphur + (4 x Atomic mass of Oxygen)

= (2x 23) + 32 + (4x 16)

= 46 + 32 + 64

= 142 g/mol

In BF₃, boron is sp² hybridized.
? shape of BF₃ = planar.
In [BH₄]^–, boron is sp3 hybridized, thus the shape is tetrahedral.

On heating boric acid above 370 K, it forms metaboric acid, HBO₂ which on further heating yields boric oxide B₂O₃.

H₃B₂O₃ → HBO₂ → B₂O₃

Boric acid is a Lewis acid since it accepts electrons from hydroxyl ion of H₂O molecule. It is not a protic acid.
B (OH)₃ + 2HOH → [B (OH)₄]^– + H₃O⁺

In BCl₃, there is only six electrons in the valence shell of B atom. Thus, the octet is incomplete and it can accept a pair of electrons from water and hence BCl₃ undergoes hydrolysis. Whereas, in CCl₄, C atom has 8 electrons and its octet is complete. That's why it has no tendency to react with water.