Chapter 7 The p Block Elements Solutions
Question - 21 : - Comment on the nature of two S−Obonds formed in SO2 molecule.Are the two S−O bonds in this molecule equal?
Answer - 21 : -
The electronic configuration of Sis 1s2 2s2 2p6 3s2 3p4.
During the formation of SO2, one electron from 3p orbitalgoes to the 3d orbital and S undergoes sp2 hybridization. Two of these orbitals formsigma bonds with two oxygen atoms and the third contains a lone pair. p-orbital and d-orbitalcontain an unpaired electron each. One of these electrons forms pπ- pπ bondwith one oxygen atom and the other forms pπ- dπ bond with the other oxygen. This is the reason SO2 has a bent structure. Also, it is aresonance hybrid of structures I and II.Both S−O bonds are equal in length (143 pm) and have amultiple bond character.
How is the presence of SO2 detected?
Answer - 22 : -
SO2 is a colourless and pungent smelling gas.
It can be detected with the help of potassiumpermanganate solution. When SO2 is passed through an acidified potassiumpermanganate solution, it decolonizes the solution as it reduces
Question - 23 : - Mention three areas in which H2SO4 plays an important role.
Answer - 23 : -
Sulphuric acid is an importantindustrial chemical and is used for a lot of purposes. Some important usesof sulphuric acid are given below.
(i) It isused in fertilizer industry. It is used to make various fertilizers such asammonium sulphate and calcium super phosphate.
(ii) Itis used in the manufacture of pigments, paints, and detergents.
(iii) Itis used in the manufacture of storage batteries.
Question - 24 : - Write the conditions to maximizethe yield of H2SO4 by Contact process.
Answer - 24 : -
Manufacture of sulphuric acid byContact process involves three steps.
1. Burningof ores to form SO2
2. Conversionof SO2 to SO3 by the reaction of the formerwith O2
(V2O5 isused in this process as a catalyst.)
3. Absorptionof SO3 in H2SO4 to give oleum (H2S2O7)
Thekey step in this process is the second step. In this step, two moles of gaseousreactants combine to give one mole of gaseous product. Also, this reaction isexothermic. Thus, in accordance with Le Chatelier’s principle, to obtain themaximum amount of SO3 gas, temperature should be low andpressure should be high.
Question - 25 : - Why is 
for H2SO4 inwater?
Answer - 25 : - 
It can be noticed that 
This is because a neutral H2SO4 hasa much higher tendency to lose a proton than the negatively charged 
. Thus, the former is a muchstronger acid than the latter.
Considering the parameters suchas bond dissociation enthalpy, electron gain enthalpy and hydration enthalpy,compare the oxidising power of F2 and Cl2.
Answer - 26 : -
Fluorine is a much strongeroxidizing agent than chlorine. The oxidizing power depends on three factors.
1. Bond dissociationenergy
2. Electrongain enthalpy
3. Hydrationenthalpy
The electron gain enthalpy ofchlorine is more negative than that of fluorine. However, the bond dissociationenergy of fluorine is much lesser than that of chlorine. Also, because of its smallsize, the hydration energy of fluorine is much higher than that of chlorine.Therefore, the latter two factors more than compensate for the less negativeelectron gain enthalpy of fluorine. Thus, fluorine is a much stronger oxidizingagent than chlorine.
Question - 27 : - Give two examples to show theanomalous behaviour of fluorine.
Answer - 27 : -
Anomalous behaviour offluorine
(i) Itforms only one oxoacid as compared to other halogens that form a number ofoxoacids.
(ii) Ionisationenthalpy, electronegativity, and electrode potential of fluorine are muchhigher than expected.
Question - 28 : - Sea is the greatest source ofsome halogens. Comment.
Answer - 28 : -
Sea water contains chlorides,bromides, and iodides of Na, K, Mg, and Ca. However, it primarily containsNaCl. The deposits of dried up sea beds contain sodium chloride and carnallite,KCl.MgCl2.6H2O. Marine life also contains iodine in theirsystems. For example, sea weeds contain upto 0.5% iodine as sodium iodide.Thus, sea is the greatest source of halogens.
Question - 29 : - Give the reason for bleachingaction of Cl2.
Answer - 29 : -
When chlorine reacts with water,it produces nascent oxygen. This nascent oxygen then combines with the colouredsubstances present in the organic matter to oxide them into colourlesssubstances.
Coloured substances +[O] → Oxidized colourless substance
Question - 30 : - Name two poisonous gases whichcan be prepared from chlorine gas.
Answer - 30 : -
Two poisonous gases that can beprepared from chlorine gas are
(i) Phosgene(COCl2)
(ii) Mustardgas (ClCH2CH2SCH2CH2Cl)