Q24 of 26 Page 1

(a) Account for the following :

(i) Acidic character increases from HF to HI.


(ii) There is a large difference between the melting and boiling points of oxygen and sulphur.


(iii) Nitrogen does not form pentahalide.


(b) Draw the structures of the following:


(i) ClF3


(ii) XeF4


OR


(i) Which allotrope of phosphorus is reactive and why ?


(ii) How are the supersonic jet aeroplanes responsible for the depletion of ozone layer ?


(iii) F2 has lower bond dissociation enthalpy than Cl2. Why ?


(iv) Which noble gas is used in filling balloons for meteorological observations ?


(v) Complete the following equation :



(a) (i) Atomic radii/size of halide ions is of the order F- < Cl- < Br- < I- . With increase in size, negative charge is dispersed throughout ions and ions gets stabilized. Thus acidity is in the order HF < HCl < HBr < HI.

(ii) This occurs due to presence of vacant d-orbital and combining forms of sulphur (S8) and these properties not being present in oxygen. Despite both being group 16 elements of the periodic table, the Sulphur molecule has 8 atoms and the oxygen molecule has two. Hence it takes more energy to convert Sulphur in a different state.


(iii) Nitrogen with n = 2, has s and p orbitals only. It does not have d orbitals to expand its covalence beyond four. That is why it does not form pentahalide.


(b) (i) The structure of ClF3 is T-shaped. There are 10 electrons surrounding the central Chlorine atom and there are five electron pairs arranged in a trigonal bipyramidal shape with a 175° F-Cl-F bond angle. There are two equatorial lone pairs which make the final structure T-shaped.



(ii) The structure Xenon tetrafluoride is square planar. There are eight electrons surrounding the central Xe atom, with fluorine linked to four electrons. There are two lone pairs of electrons symmetrically distributed around the xenon central atom.




OR


(i) White phosphorus is less stable and thus most reactive of all the allotropes of phosphorous. It is because of the presence of angular strain in the P4 discrete tetrahedral units where the angles are 60°, which makes it highly reactive. It readily catches fire in air to give dense white fumes of P4O10.


(ii) The exhaust emitted from supersonic jet aeroplane contains CO2, NO, by-products of petrochemicals, and other particles which are the killers of stratospheric ozone layer along with the supersonic sound produced by these aeroplanes which contribute to pollution and destroy the ozone layer.


(iii) Due to the smaller size and high electro-negativity of fluorine more energy is required to break the bond of F2 molecule than Cl2. Thus F2 has lower bond dissociation energy than Cl2.


(iv) Helium (He) gas is used in filling balloons for meteorological observations because it is non-inflammable and a lightweight gas.


(v) XeF2 + PF5→ [XeF]+ [PF6]-. Xenon fluorides on reaction with fluoride ion acceptors form cationic species and fluoride ion donors form fluoroanions.


More from this chapter

All 26 →
22

Write the names and structures of the monomers of the following polymers:

(i) Terylene


(ii) Buna-S


(iii) Neoprene


 23

Seeing the growing cases of diabetes and depression among young children, Mr. Chopra, the principal of one reputed school organized a seminar in which he invited parents and principals. They all resolved this issue by strictly banning junk food in schools and introducing healthy snacks and drinks like soup, lassi, milk, etc. in school canteens. They also decided to make compulsory half an hour of daily physical activities for the students in the morning assembly. After six months, Mr. Chopra conducted the health survey in most of the schools and discovered a tremendous improvement in the health of the students.

After reading the above passage, answer the following questions:


(i) What are the values (at least two) displayed by Mr. Chopra ?


(ii) As a student, how can you spread awareness about this issue?


(iii) Why should antidepressant drugs not be taken without consulting a doctor?


(iv) Give two examples of artificial sweeteners.


 25

An aromatic compound ‘A’ of molecular formula C7H6O2 undergoes a series of reactions as shown below. Write the structures of A, B, C, D and E in the following reactions :


OR


(a) Write the structure of main products when benzene diazonium chloride reacts with the following reagents :


(i) H3PO2 + H2O


(ii) CuCN/KCN


(iii) H2O


(b) Arrange the following in the increasing order of their basic character in an aqueous solution:


C2H5NH2, (C2H5)2NH, (C2H5)3N


(c) Give a simple chemical test to distinguish between the following pair of compounds:


C6H5 – NH2 and C6H5 – NH – CH3


 26

For the hydrolysis of methyl acetate in aqueous solution, the following results were obtained :

(a) Show that it follows pseudo first order reaction, as the concentration of water remains constant.


(b) Calculate the average rate of reaction between the time interval 10 to 20 seconds.


(Given: log 2 = 0.3010, log 4 = 0.6021).


OR


(a) For a reaction A + B → P, the rate is given by Rate = k[A][B]2


(i) How is the rate of reaction affected if the concentration of B is doubled ?


(ii) What is the overall order of reaction if A is present in large excess ?


(b) A first order reaction takes 30 minutes for 50% completion. Calculate the time required for 90% completion of this reaction.