REASONING QUESTION AND ANSWERS
1. What is the highest oxidation state shown by the element belongs to sixteenth group?
Ans: 16 – 10 = 6
Highest oxidation state = group number – 10
2. What property of AlCl3 made it to use as a catalyst in organic synthesis?
Ans: Lewis acid character.
3. Define inert pair effect?
Ans: Reluctance of paired ‘S’ electrons to participate in chemical bond is known as inert pail effect. Such reluctance is increases from top to bottom due to increase in the pairing energy.
4.The stability of divalent state increases in the order Ge<Sn<Pb. Explain.
Ans: Due to inert pair effect
5. What are zeolites?
Ans: These are alumino silicates and act as shape selective catalysts and softening the hard water.
6. Which type of structure is present in B-cristabalite?
Ans: It has Zinc blende structure.
7. N2 is chemically Inert?
Ans: Due to its high bond dissociation energ y N ≡ N.
8. Sulphur behaves paramagnetic at high temperature. Explain.
Ans: At high temperatures
9. O2 is a gas where as Sulphur is a solid at room temperature
(or)
O2 is a linear molecule but Sulphur exists S8 puckered ring structure?
Ans: Since Oxygen is in small size it can form pπ - pπ multiple bonds and exist with linear molecule with weak inter particle attractions where as Sulphur is in large size it cannot form multiple bonds and exist in solid state with puckered (S8) ring structure.
10. Thermal stabilty of Hydrides decreases in the order H2O>H2S>H2Sc>H2Te>H2Po.
Ans: As the size of atom increases from O to Po M-H bond strength decreases. Hence Thermal stability decreases.
11. H2O is a liquid, where as H2S is gas. Explain.
Ans: Due to inter molecular Hydrogen bond present in water molecules.
Ans: From H2S to H2Te B.P increases due to increase in the size, Vanderwaals forces increases, but H2O due to inter molecular H-bond.
13. Account for the statement. Bond angle of 16th group hydrides decreases from H2O to H2Te.
Ans: H2O>H2S>H2Sc>H2Te
It is due to decrease vin the electronegativity from Oxygen to the Te repulsion decreases, hence bond angle decreases.
14. Acidity of 16th group hydrides is H2O <H2S <H2Sc < H2Te <H2PO . Explain.?
Ans: As the size of the central atom increases M-H bond strength decreases hence Acidity increases.
15. SF6 is a non toxic & chemically inert. Comment.
Ans: Inertness of SF6 is due to the presence of sterically protected ‘S’ atom by ‘F’ atoms, which does not allow thermodynamically favourable reactions like Hydrolysis.
16. What properties of SF6 made it use as a gaseous insulator in high voltage generators?
Ans: Due to its chemical Inertness.
17. The X-X bond energies of Halogens is Cl2>Br2>F2>I2. Comment?
Ans: Bond energy decreases from Br2 to I2 as the size of atom increases its bond distance increases, hence Bond energy is decreased. Abnormally F2 has low bond dissociations energy inspite of its small size& small bond length, it is due to extreme small size of ‘F’ causes electron-electron repulsions of the lone pairs.
18.. Ionic character of the metal halides decreases as follows, Explain.
M-F > M-Cl > M-Br > M-
Ans: Due to electronegativity difference between inter halogens their bond dissociation energy is less than halogens. Hence inter halogens are more reactive.(x-xI < x-x Bond dissociation energy).
19. HF is a liquid where as
other hydrogen halides are gases. Explain?.
Ans: Due to intermolecular hydrogen bond in HF
20. Comment on the following
trend mentioned against their property
HF>HI>HBr>HCl (boiling point)
HF>HCl>HBr>H-I (acidic character)
Ans: As the size of the atom increases Vanderwaal’s attraction increases boiling point increases. Abnormally HF has high boiling due to intermolecular hydrogen bond. Since the size of atom increases from F to I , bond length of H-X increases, bond strength decreases
21. Treatment of metal chlorides with H2 SO4 gives Hydrogen Chloride, where as metal Bromides & Iodides with conc.H2SO4is not satisfactory for the preparation of HBr &HI explain?
Ans: conc. H2SO4 can oxidise Br- & I- in to Br2& I2 hence it is not a satisfactory method
22. Care must be taken while
using chlorine oxides as oxidising agents. Explain.
Ans: Chlorine oxides can act as powerful oxidising agents ,which can
decompose explosively by
mechanical shock are heating .
23. The acidic strength oxoacids of halogens is as follows.
a) HOF > HOCl > HOBr > HOI (Increasing Pka or decreasing
acidity)
b) HOCl < HClO2 < HClO3 < HClO4 (Increasing acidity or decreasing pka value)
Ans: a)As the electro negativity decreases from F to I it’s acidity decreases.
b) As the no. of oxygens atoms increases stability anion increases and acidity increases
24. With what neutral molecule is ClO- isoelectronic?
Ans: Species with equal number of electrons are known as isoeletronic. ClO-is isoelectronic with ClF.
25. Why noble gases are chemically inert?
Ans: Because of high IE, zero electron affinity (electron gain enthalpy) and stable electronic configuration.
26. Compounds of Xe are known but the compounds of He and Ne are not known. Comment.
Ans: Due to absence of empty d-orbitals in He and Ne, paired electrons cannot excite and no chemical bonding.
27. What made Neil Barlett to discover the first noble gas compound, Xe+ (Pt F6) in the year 1962 ?
Ans: Barlett has noticed that PtF6 react with oxygen to form O2+ (PtF-)and since ionization enthalpies of O2 & Xe are comparable (1175 & 1170). He reasoned that PtF6 would react with Xe to from Xe+ (PtF6)-.
28. NF3 is a pyramidal, where BF3 is planar, explain.
Ans: NF3 has 3 bonding pair(bp) & one lone pair(lp) = 4 sp hybridisation pyramidal
BF3 has only 3 bp, sp2 hybridisation, planar.
29. Arrange the following oxides in the increasing order of their acidity? As2O3 , ClO2 , GeO2 , Ga2O3
Ans: Ga2O3 < GeO2 < As2O3 < ClO2
As electro negativity increases from Ga < Ge < As < Cl their acidity increases.
30. Electrolysis of KBr(aq) gives Br2 at anode but that of KF(aq) does not gives F2. give reasons for disparity in behaviour?
Ans: Oxidation potential value of Br- is more than water, where as F- is less than water. At anode high oxidation potential ion under goes oxidation
31. (SiF6)-2 exist but (CF6)-2 does not.why?
Ans: Si can increases it’s co oxidation number 4 to 6, but ‘C’ cannot die to absence of empty d – orbital.
32. On being slowly passed through water PH3 forms bubbles but NH3 dissolves. Why is it so?
Ans: Due to inter molecular H – bond between water & ammonia, it is soluble where as pH3 is in soluble.
33.. Why is OF3 compound not known?
Ans: oxygen does not have d – orbital, hence it cannot it’s valency.
34 . Which of the following is more covalent : SbCl5 or SbCl3
Ans: Higher oxidation state more covalent. Hence SbCl5 is more covalent.
35 Most of the known noble gas compounds are those of xenon. Explain
Ans: Because ionisation enthalpy of Xe is lower than the He, Ne, and Ar, Kr, hence it can form the compounds easily.
36 ClF3 exist but not FCl3. Explain
Ans: 1) F is more electronegative than the Cl hence it can not show +ve oxidation state
2) due to absence of empty d orbitals in F it can not show 3 oxidation state
37. The first ionisation enthalpy of ‘N’ is greater than the oxygen. Explain
Ans: Due to stable oxidisation state of ‘N’ 2S2 2P3 it has high ionisation enthalpy
38. OF2 is called oxygen difloride but not florine oxide. Explain
Ans: ‘F’ is more electronegative than the oxygen , hence fluoride (F-) is formed and called as oxygen difloride
39. SF6 is known but SH6 is not know?
Ans: Always higher oxidations states can be shown, only when they combine with more electronegative elements like ‘F’ and ‘ O’.
40. Elements of group 16 generally show lower value of first ionization enthalpy compared to the corresponding periods of group 15. why?
Ans- Due to extra stable half filled p orbitals electronic configuration of Group 15 elements, larger amount of energy is required to remove electrons compared to Group 16 elements.
41. H2S is less acidic than H2Te. Why?
Ans.-Due to the decrease in bond dissociation enthalpy down the group, acidic character increases.
42. What happens when
a. Conc. H2SO4 is added to calcium fluoride
b. SO3 is passed through water?
Ans:- (i) It forms hydrogen fluoride
CaF2 + H2SO4 ® CaSO4 + 2HF
(ii).It dissolves SO3 to give H2SO4
SO3 + H2O ® H2SO4
c. Halogens have maximum
negative electron gain enthalpy in the respective periods of the periodic
table. Why?
Ans:- Halogens have the smallest size in their respective periods and therefore high effective nuclear charges. As a consequence, they readily accept one electron to acquire noble gas electronic configuration.
d. Although electron gain
enthalpy of fluorine is less negative as compared to chlorine, fluorine is a
stronger oxidizing agent than chlorine. Why?
It is due to (i) low enthalpy of dissociation of F – F bond (ii) High hydration enthalpy of F-.
e. Fluorine exhibits only –1
oxidation state whereas other halogens exhibit +1, +3, +5, and +7 oxidation
states also explain?
Fluorine is the most electronegative element and cannot exhibit any
positive oxidation state. Other halogens have d orbitals and therefore, can
expand their octets and show +1, +3, +5,
and +7 oxidation states also.
f.
Write the balanced chemical equation for the reaction of Cl2
with hot and concentrated NaOH. Is this reaction a disproportionation reaction?
Justify.
3Cl2 + 6NaOH
®
5NaCl + NaClO3 + 3
H2O
Yes, chlorine from zero oxidation state is changed to –1 and +5 oxidation state.
g. When HCl reacts with finely powdered iron, it forms ferrous chloride
and not ferric chloride why?
Its reaction with iron produces H2
Fe +
2HCl ® FeCl3 + H2
Liberation of hydrogen prevents the formation of ferric chloride.
h . Why are the
elements of Group 18 known as noble gases?
The elements present in Group 18 have their valence shell orbitals completely filled and, therefore react with a few elements only under certain conditions. Therefore, they are known as noble gases.
i. Noble gases have very low
boiling points. Why?
Noble gases being monoatomic have no interatomic forces except weak
dispersion forces and therefore, they are liquefied at very low temperature.
Hence they have low boiling points.
43 Does the hydrolysis of XeF6 lead to a redox reaction?
Ans- No, the products of hydrolysis are XeOF4 and XeO2F2 where the oxidation states of all the elements remain the same as it was in the reacting state.
44. Why is H2O a liquid and H2S a gas?
Ans- Because of small size and high electronegativity of oxygen, molecules of water are highly associated through hydrogen bonding resulting in its liquid state.
46. Which of the following does not react with oxygen directly? Zn, Ti, Pt, Fe.
Ans:- Pt
47. Complete the following reaction
(i) C2H4 + O2 ®
(ii) 4Al + 3 O2 ®
Ans:- (i) C2H4 + 3O2 ® 2CO2 + 2H2O
(ii) 4Al + 3 O2 ® 2Al2O3
48. Why does O3 act as a powerful oxidizing agents?
Ans.- Due to the case with which it liberates atoms of nascent oxygen
( O3 ® O2 + O ) it acts as a powerful oxidizing agent.
49. How is O3 estimated quantitatively?
Ans- When ozone reacts with an excess of potassium iodide solution buffered with a borate buffer (pH = 9.2) , iodine is liberated which can be titrated against a standard solution of sodium thiosulphate. This is a quantitative method for estimation of O3 gas.
50. What happens when sulphur dioxide is passé through an aqueous solution of Fe(III) salt?
Ans:-
2 Fe+3 + SO2 + 2 H2O ® 2 Fe+2 + SO42- + 4H+
50. Comment on the nature of two S – O bonds formed in SO2 molecule. Are the two S – O bonds in this molecules equal?
Ans- Both the S – O bonds are covalent and have equal strength due to resonating structures
51. Why is Ka2 << Ka1 for H2SO4 in water?
Ans- H2SO4 is a very strong acid in water largely because of its first ionization to H3O+ and HSO4-. The ionization of HSO4- to H3O+ and SO42- is very very small. That is why
Ka2 << Ka1
52. Give the reason for bleaching action of Cl2
Ans- It is a powerful bleaching agent, bleaching action is due to oxidation.
Cl2 + H2O ® 2 HCl + O
Coloured substance + O ® Colourless substance
53. Name two poisonous gases
which can be prepared from chlorine
gas?
Ans- Phosgene
(COCl2), Tear gas (CCl3NO2,
Mustard gas ( ClCH2CH2SCH2CH2Cl)
54.Why is ICl more reactive than I2?
Ans- In general interhalogen compounds are more reactive than halogens due to weaker X – X1 bonding than X – X bond. Thus , ICl is more reactive than I2
55. Why is helium used in diving apparatus?
Ans- It is used as a diluent for oxygen in modern diving apparatus because of its very low solubility in blood.
56.Why has it been difficult to study the chemistry of radon?
Ans-Radon is radioactive with very short half life which makes the study of chemistry of radon difficult.
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