Q24 of 26 Page 1

(a) Account the following:

(i) Acidic character increases from HF to HI.


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


(iii) Nitrogen does not form pentahalide.


(b) Draw the structures of the following:


(i) ClF3 : it has a bent –T shape


(ii) XeF4 : it has square planar geometry.


OR


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


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


(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 equation:



(i) An acid is a molecule which easily releases H+ ions. HF, HCl, HBr and HI are acidic in nature. They all belong to the 17th group and are called halo acids. As we go down the group bond dissociation energy decrease implies the H-X bond is weaker down the group. Weaker the bond lesser energy required to break the bond, hence acidic character increases down the group.

(ii) Oxygen exits as O2, while sulphur exists as S8. Diatomic oxygen have less surface area while polyatomic sulphur will have surface area hence higher boiling and melting points.


(iii) Nitrogen belongs to 2nd period so has only ‘s’ and ‘p’ shells. Normally it can form 3 bonds as its electronic configuration of valence shell is[He]2s22p3 , but can form a maximum of 4 bonds( 3 covalent and 1 coordinate bond). The other members of this group have vacant d- orbitals available so can expand their octate and form pentavalent halides but not nitrogen.


(b)


(i)



(ii)



OR


(i) The chemical property of some elements to exist in two or more forms in the same physical state is called allotropism. Phosphorous exists in many forms out of which white phosphorus is highly reactive. White phosphorus exists as P4 and has a geometry of tetrahedron causing angular strain leading to high reactivity.


(ii) The supersonic jet aeroplanes fly in stratosphere near to the ozone layer and the fuel exhausts contain nitrogen oxide which readily combines with ozone to give nitrogen di oxide and O2 leading to depletion of ozone layer.


(iii) The size of F2 molecule is smaller than that of Cl2 molecule, because of which the inter electronic repulsions of the electrons in outermost orbital of F2 are greater leading to lower bond dissociation enthalpy.


(iv) Helium is the noble gas used in filling balloons for meteorological observations due to its light weight, inertness and non-inflammability.


(v)


More from this chapter

All 26 →
22

Give reasons:

(a) n-Butyl bromide has higher boiling point than t-Butylbromide.


(b) Racemic mixture is optically inactive.


(c) The presence of nitro(-NO2) at o/p positions increases the reactivity of haloarenes towards nucleophilic substitution reactions.


 23

Mr.Roy, the principal of one reputed school organised a seminar in which he invited parents and principals to discuss the serious issue of diabetes and depression in students. They also resolved this issue by strictly banning the junk foods in school and to introduce healthy snacks and drinks like soup, lassi, milk etc., in school canteens. They also decided to make compulsory half an hour physical activity for the students in the morning assembly daily. After six months, Mr.Roy conducted the health survey in most of the schools and discovered a tremendous improvement in the health of students.

After reading the above passage answer the following:


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


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


(iii) What are tranquilizers? Give an example.


(iv) why is use of aspartame limited to cold foods and drinks?


 25

An aromatic compound ‘A’ of molecular formula C7H7ON undergoes a series of reactions as shown below. Write the structure of A,B,C,D and E in the following reactions:


OR


(a) Write the structures of main products when aniline reacts with the following reagents:


(i) Br2 water


(ii) HCl


(iii) (CH3CO)2O/pyridine


(b) Arrange the following in the increasing order of their boiling point:


C2H5NH2 , C2H5OH, (CH3)3N


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


(CH3)2NH, (CH3)3N


 26

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


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


(ii) Calculate the average rate of reaction, between the time interval30 and 60 seconds. (given: log 2= 0.3010, log 4 = 0.6021)


OR


(a) For a reaction , the rate is given by Rate


(i) How is the rate of reaction effected 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. (log 2 =0.3010)