Q26 of 26 Page 1

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)


(i) For a first order reaction half-time of a reaction is independent of concentration of the reacting species. Half-time of a first order is given by

. So from the equation we know that reaction half-time is dependent on rate constant(k). Rate constant(k) of a first order reaction is given by



The reaction should be of first order with respect to methyl acetate, when concentration of water is constant to be a pseudo first order reaction. So, let us check the rate constant at different time intervals, if it is constant irrespective of the concentration then is a pseudo first order reaction. Substituting the time and concentration values given in the table in the rate constant equation:



Since the rate constant is independent of the concentration of the ester, hydrolysis of esters in excess of water is indeed a pseudo first order reaction.


(ii) M/s


OR


(a)


(i) rate is directly proportional to concentration of B and the reaction is of second order with respect to B. So when concentration of B is doubled rate becomes four times.


(ii) When A is present in large excess, the reaction becomes independent of the concentration of A, so the overall order of the reaction will be 2.


(b)








More from this chapter

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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?


 24

(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:



 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