(a) Account for the following:

(i) Bond angle in N is higher than NH₃.

(ii) H₂S has lower boiing point than H₂O.

(iii) Reducing character decreases from SO₂ to TeO₂.

(b) Draw the structures of the following:

(i) H₄P₂O₇ (Pyrophosphoric acid)

(ii) XeF₂

OR

(a) Draw the structures for the following:

(i) XeF₄

(ii) H₂S₂O₇

(b) Account for the following:

(i) Iron on reaction with HCl forms FeCl₂ and not FeCl_3.

(ii) HClO₄ is a stronger acid than HClO.

(iii) BiH₃ is the strongest reducing agent amongst all the hydrides of group 15.

(a)

(i)

In ammonia molecule there is a lone pair present. We know that repulsion is of the order: lp-lp>lp-bp>bp-bp where lp is lone pair and bp is bond pair. Since there is lp-bp repulsion, lp occupies more space and hence bond angle gets decreased. While in ammonium ion there is no lone pair present so the bond angle is greater.

(ii)

In H₂O molecule, H is attached to a highly electronegative atom. So there is Hydrogen bond formed between H of one molecule and O of another molecule. Through this bonding water exist as a network of molecules. These bonds are strong enough and hence H₂O has a higher boiling point. While in H₂S molecule there is no such possibility of H-bonding since it is a less electronegative element. Therefore it has a low boiling point when compared to H₂O.

(iii) As we know size of the elements decreases down the group. So electronegativity decreases down the group because of which metallic character increases down the group. As metallic character increases reducing character decreases. Also due to inert pair effect lower oxidation states are stable on moving down the group which also says that reducing character decreases. Therefore, reducing character decreases from SO₂ to TeO₂.

(b)

(i) H₄P₂O₇ (Pyrophosphoric acid)

(ii) XeF₂

OR

(a)

(i) XeF₄

(ii) H₂S₂O₇

(b)

(i) when Iron is treated with HCl, the reaction releases H₂ gas. Therefore ferrous chloride (FeCl₂) is formed instead of ferric chloride (FeCl₃).

Fe + 2HCl → FeCl₂ + H₂

(ii)

In the above molecules, hydrogen bonded to oxygen is called the acidic proton. Acidity of a compound is defined as the ease with which it release proton. For the proton to be released easily the O-H bond must be weaken. On increasing the oxidation Number of the central atom to which O-H bond is connected acidity is increased. Since in HClO₄, Cl atom is connected to 3 more O atoms bond strength weakens and acidity increases. Whereas in HClO, oxidation number of Cl atom remains the same so its proton is less acidic.

(iii) On moving down the 15^th group, bond dissociation enthalpy decreases which means that these bonds are quite easy to break. Consequently, reducing character also decreases. Hence, Bi being the last element shows strong reducing property.