P Block Elements

7.39

Nitrogen is prepared in the laboratory by heating aqueous ammonium chloride (NH₄Cl) with sodium nitrite (NaNO₂) to form ammonium nitrite (NH₄NO₂), which is unstable. Ammonium nitrite breaks down to form nitrogen and water.

NH₄Cl (aq) + NaNO₂ (aq)  - NH₄NO₂ + NaCl (aq)

NH₄NO₂  - N₂ (g)+ H₂O (l)

Small amounts of NO and HNO₃ are also produced which can be removed by passing nitrogen gas through aqueous sulphuric acid containing potassium dichromate.

7.38 

The electronegativity of N (3.0) is higher than that of P (2.1). Due to this N-H bond is more polar than a

P-H bond. Also, P and H have the same electronegativity of 2.1 i.e., the P-H bond is non-polar. Therefore, PH₃ does not form hydrogen form.

The structure of NH₃ and PH₃ with their electronegativity is represented below.

7.2

Nitrogen atom can bond with another nitrogen atom by strong p–p overlap resulting in NN. The triple bond in N₂ has high bond strength resulting in high bond dissociation energy. Phosphorous do not show this property of p–p overlap. Hence, nitrogen is less reactive than phosphorous.

The p-orbitals which interact to form two? bonds in N₂ molecule are shown by joining them with a curve line.

7.34

It is difficult to study the chemistry of radon because it is a radioactive substance having a half-life (the time period to decompose the substance half to its initial concentration) of only 3.82 days.

Radon belongs to the 18 group elements with chemical formula as Rn. In general, the elements at the bottom o periodic table are radioactive, they are very dangerous to study as they emit harmful radiations.

Also, compounds of radon such as RnF₂ have not been isolated, they are still in the phase of discovery. They have only been identified by radiotracer technique and no any further properties have been determined.

7.33

XeF₆ + H₂O  XeO₂F₂ + HF

Balanced equation: XeF₆ + 2H₂O XeO₂F₂ +4HF. The steps for balancing the reaction are as follows:

1. The main element is First, check if the atoms of Xe on both sides are balanced. YES, they are.

2. Then take another element i.e. F. It is not balanced on the right side, there are 3 atoms of F missing. So, to balance it multiply HF by 4.

3. Now check the other secondary atoms which are oxygen and hydrogen. Oxygen is not balanced on the left side as there are 2 O atoms so multiply H₂O by

4. Now check for the hydrogen They are balanced on both sides.

7.32

Helium mixed with oxygen under pressure is given to sea divers for respiration because pure oxygen can be toxic at a great concentration at the depth. Therefore oxygen can be mixed with helium to reduce oxygen concentration while eliminating nitrogen. 

The main reason for adding helium to the breathing mix is to reduce the proportion of nitrogen and oxygen below those of air, to allow the gas mix to be breathed safely on deep dives.

A low proportion of nitrogen is required to reduce nitrogen narcosis and other physiological effects of gas at depth.

7.30

Two poisonous gases that can be prepared with chlorine gas are:

Phosgene (COCl₂)

This is how phosphene is formed:

CO + Cl₂? COCl₂ (in presence of sunlight)

(ii) Mustard gas (Cl-C₂H₄-S-C₂H₄-Cl)

(iii) Tear gas (CCl₃NO₂)