Chapter 7 The p Block Elements Solutions
Question - 31 : - Why is ICl more reactive than I2?
Answer - 31 : -
ICl is more reactive than I2 becauseI−Cl bond in ICl is weaker than I−I bond in I2.
Question - 32 : - Why is helium used in divingapparatus?
Answer - 32 : -
Air contains a large amountof nitrogen and the solubility of gases in liquids increases with increase inpressure. When sea divers dive deep into the sea, large amount of nitrogendissolves in their blood. When they come back to the surface, solubility ofnitrogen decreases and it separates from the blood and forms small air bubbles.This leads to a dangerous medical condition called bends. Therefore, air inoxygen cylinders used for diving is diluted with helium gas. This is done as Heis sparingly less soluble in blood.
Question - 33 : - Balance the following equation:XeF6 + H2O → XeO2F2 +HF
Answer - 33 : -
Balanced equation
XeF6 + 2 H2O → XeO2F2 +4 HF
Question - 34 : - Why has it been difficult tostudy the chemistry of radon?
Answer - 34 : -
It is difficult to study thechemistry of radon because it is a radioactive substance having a half-life ofonly 3.82 days. Also, compounds of radon such as RnF2 have notbeen isolated. They have only been identified.
Question - 35 : - Discuss the generalcharacteristics of Group 15 elements with reference to their electronicconfiguration, oxidation state, atomic size, ionisation enthalpy andelectronegativity.
Answer - 35 : -
General trends in group 15elements
(i) Electronicconfiguration: All the elements in group 15 have 5 valence electrons.Their general electronic configuration is ns2 np3.
(ii) Oxidationstates: All these elements have 5 valence electrons and require threemore electrons to complete their octets. However, gaining electrons is verydifficult as the nucleus will have to attract three more electrons. This cantake place only with nitrogen as it is the smallest in size and the distancebetween the nucleus and the valence shell is relatively small. The remainingelements of this group show a formal oxidation state of −3 in their covalentcompounds. In addition to the −3 state, N and P also show −1 and −2 oxidationstates.
All the elements present in thisgroup show +3 and +5 oxidation states. However, the stability of +5 oxidationstate decreases down a group, whereas the stability of +3 oxidation stateincreases. This happens because of the inert pair effect.
(iii) Ionizationenergy and electronegativity
First ionization decreases on movingdown a group. This is because of increasing atomic sizes. As we move down agroup, electronegativity decreases, owing to an increase in size.
(iv) Atomicsize: On moving down a group, the atomic size increases. This increasein the atomic size is attributed to an increase in the number of shells.
Question - 36 : - Why does the reactivity ofnitrogen differ from phosphorus?
Answer - 36 : -
Nitrogen is chemically lessreactive. This is because of the high stability of its molecule, N2.In N2, the two nitrogen atoms form a triple bond. This triple bondhas very high bond strength, which is very difficult to break. It is because ofnitrogen’s small size that it is able to form pπ−pπ bonds with itself.This property is not exhibited by atoms such as phosphorus. Thus, phosphorus ismore reactive than nitrogen.
Question - 37 : - Discuss the trends in chemicalreactivity of group 15 elements.
Answer - 37 : -
General trends in chemicalproperties of group − 15
(i) Reactivitytowards hydrogen:
The elements of group 15 reactwith hydrogen to form hydrides of type EH3, where E = N, P, As, Sb,or Bi. The stability of hydrides decreases on moving down from NH3 toBiH3.
(ii) Reactivitytowards oxygen:
The elements of group 15form two types of oxides: E2O3 and E2O5,where E = N, P, As, Sb, or Bi. The oxide with the element in the higheroxidation state is more acidic than the other. However, the acidic characterdecreases on moving down a group.
(iii) Reactivitytowards halogens:
The group 15 elements react withhalogens to form two series of salts: EX3 and EX5.However, nitrogen does not form NX5 as it lacks the d-orbital.All trihalides (except NX3) are stable.
(iv) Reactivitytowards metals:
Thegroup 15 elements react with metals to form binary compounds in which metalsexhibit −3 oxidation states.
Question - 38 : - Why does NH3 formhydrogen bond but PH3 does not?
Answer - 38 : -
Nitrogen is highlyelectronegative as compared to phosphorus. This causes a greater attraction ofelectrons towards nitrogen in NH3 than towards phosphorus in PH3.Hence, the extent of hydrogen bonding in PH3 is very less ascompared to NH3.
Question - 39 : - How is nitrogen prepared in thelaboratory? Write the chemical equations of the reactions involved.
Answer - 39 : -
An aqueous solution of ammoniumchloride is treated with sodium nitrite.
NO and HNO3 areproduced in small amounts. These are impurities that can be removed on passingnitrogen gas through aqueous sulphuric acid, containing potassium dichromate.
Question - 40 : - How is ammonia manufacturedindustrially?
Answer - 40 : -
Ammonia is prepared on alarge-scale by the Haber’s process.
