Chemistry

The p-Block Elements.

Question:

Why does the reactivity of nitrogen differ from phosphorus?

Answer:

N2 exist as a diatomic molecule containing triple bond.batoeen two N-atoms. Due to the presence —of triple bond betweep the two N-atoms, the bond dissociation energy is large (941 .4 kJ mol-1 ). As aresult of this N2 is inert and unreactive whereas, phosphorus exists as a tetratomic molecule, containg P – P single bond. Due to the presence of single bond, the bond dissociation energy is weaker (213 kJmol-1 ) than N a N triple bond (941 .4 kJ mol-1 ) and moreover due to presence of angular strain in P4 tetrahedra. As a result of this, phosphorus is much more reactive than nitrogen.

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The p-Block Elements.

Q 1.

How is O3 estimated quantitatively?

Q 2.

Assertion (A): Both rhombic and monoclinic sulphur exist as S8 but oxygen exists as OÏ€.
Reason (R): Oxygen forms pπ-pπ multiple bond due to small size and small bond length but pπ-pπ bonding is not possible in sulphur.

Q 3.

In the preparation of H2S06 by contact process, why is S03 not absorbed directly in water to form H2S04?

Q 4.

Write the structure of pyrophosphoric acid.

Q 5.

Why is nitric oxide paramagnetic in gaseous state but the solid obtained on cooling is diamagnetic?

Q 6.

Assertion (A): NaCl reacts with concentrated H2SO4  to give colourless fumes with pungent smell. But on adding MnO2  the fumes become greenish yellow.
Reason (R): MnO2 oxidises HCl to chlorine gas which is greenish yellow.

Q 7.

Give two examples to show the anomalous behaviour of fluorine.

Q 8.

Why has it been difficult to study the chemistry of radon?

Q 9.

Why are halogens coloured?

Q 10.

List the uses of neoirand argon gases.

Q 11.

Which of the following statements are true?
(a) Only type of interactions between particles of noble gases are due to weak dispersion forces.
(b) Ionisation enthalpy of.molecular oxygen is very close to that of xenon.
(c) Hydrolysis of XeF6 is a redox reaction.
(d) Xenon fluorides are not reactive.

Q 12.

Write a balanced chemical equation, for the reaction showing catalytic oxidation of NH3 by atmospheric oxygen.

Q 13.

Name three oxoacids of nitrogen. Write the disproportionation reaction of that oxoacid of nitrogen in which nitrogen is in +3 oxidation state.

Q 14.

Match the formulas of oxides given in Column I with the type of oxide given in Column II and mark the correct option.
ncert-exemplar-problems-class-12-chemistry-p-block-elements-47

Q 15.

 Why is BiH3 the strongest reducing agent amongst all the hydrides of group 15 elements? (C.B.S.E. 2013)

Q 16.

 What is the covalence of nitrogen in N2O5 ?

Q 17.

Why is H2O a liquid and H2S a gas?

Q 18.

Give the resonating structures of N02 and N2O5.

Q 19.

 Why does R3P=0 exist but R3N=0 does not (R is an alkyl group) ?

Q 20.

 Write balanced equations for the following:
(i) NaCl is heated witlrsulphuric acid in the presence of MnO2
(ii) Chlorine gas is passed into a solution of Nal in water.

Q 21.

Why are pentahalides more covalent than trihalidcs ?

Q 22.

Why is BiH3 the strongest reducing agent amongst all the hydrides of Group 15 elements?

Q 23.

Comment on the nature of two S-O bonds formed in S02 molecule. Are the two S-O bonds in this molecule equal ?

Q 24.

Mention three areas in which H2SO4 plays an important role.

Q 25.

Discuss the trends in chemical reactivity of group 15 elements.

Q 26.

Explain why NH3 is basic while BiH3 is only feebly basic.

Q 27.

Explain why fluorine forms only one oxoacid, HOF.

Q 28.

What are the oxidation states of phosphorus in  the following: –
(i) H3PO3 (ii)PCl3
(iii) Ca3P2(iv)Na3PO4
(v) POF3

Q 29.

Arrange the following in the order of property  indicated for each set: –
(i) F2 , Cl2 , Br2 , I2 – increasing bond dissociation enthalpy.
(ii) HF, HCI, HBr, HI – increasing acid . strength.
(iii) NH3, PH3, AsH3, SbH3, BiH3 – increasing Sol. base strength.

Q 30.

On heating ammonium dichromate and barium azide separately we get
(a) N2 in both cases
(b) N2 with ammonium dichromate and NO with barium azide
(c) N2O  with ammonium dichromate and N2 with barium azide
(d) N2O with ammonium dichromate and N2O with barium azide

Q 31.

Which of the following is correct for P4 molecule of white phosphorus?
(a) It has 6 lone pairs of electrons (b) It has six P – P single bonds
(c) It has three P – P single bonds (d) It has four lone pairs of electrons,

Q 32.

In the ring test of NO3 ion.Fe2+ion reduces nitrate ion to nitric oxide, which combines with Fe2+  (aq.) ion to form brown complex. Write the reactions involved in the formation of brown ring.

Q 33.

Match the items of Column I and Column II and mark the correct option.
ncert-exemplar-problems-class-12-chemistry-p-block-elements-49
ncert-exemplar-problems-class-12-chemistry-p-block-elements-50

Q 34.

 What happens when white phosphorus is heated with concentrated NaOH solution in an inert atmosphere of CO2?

Q 35.

 Write the order of thermal stability of the – hydrides of Group 16 elements.

Q 36.

Give the reason for bleaching action of Cl2.

Q 37.

How is ammonia manufactured industrially?

Q 38.

Explain why NH3 is basic while BiH3 is only feebly basic.

Q 39.

Justify the placement of O, S, Se, Te and Po in the same group’of the periodic table in terms of electronic configuration, oxidation state and hydride formation.

Q 40.

 Knowing the electron gain enthalpy values of O—>O– and O—>O2- as -141 and 702 kJ mol-1 respectively, how can you account for the formation of a large number of oxides having O2- species and not O–?

Q 41.

Write the reactions of F2 and Cl2 with water.

Q 42.

What are the oxidation states of phosphorus in the following: –
(i) H3PO3 (ii)PCl3
(iii) Ca3P2(iv)Na3PO4
(v) POF3

Q 43.

 With which neutral molecule is ClO– isoelectronic? Is this molecule Lewis acid or base ? (Pb. Board 2009)

Q 44.

Give the formula and describe the structure of a noble gas species which is isostructural with: (i) ICI4– (ii) IBr2– (iii) Br03–

Q 45.

What is the covalence of nitrogen in N2O5 ?

Q 46.

Write a balanced equation for the hydrolytic reaction of PC is in heavy water.

Q 47.

What happens when H3PO4 is heated?

Q 48.

Which of the following does not react with oxygen directly?  Zn, Ti, Pt, Fe

Q 49.

Complete the following reactions:
(i)C2H2  + O2 -> (ii) 4Al + 3 O2 ->

Q 50.

Why does NH3 form hydrogen bond but PH3 does not?