University of Delhi 2008 B.Sc Chemistry physical - xvii - Question Paper

Q1. discuss any 4 of the subsequent :

a) Chemisorption is monolayer whereas physical adsorption is usually multilayer.

b) How can liquid junction potential be eliminated ?

c) Role of phosphoric acid in the volumetric titration of Fe2+ ions Cr2O72- ions,
Using diphenylamine as internal indicator.

d) Reaction of 3rd and higher order are not very common.

e) Difference ranging from stationary and non-stationary chain reactions.


part A

Q2. (a)Derive an expression to determine the right value of the half cell potential by graphical method.

(b) provided the cell

Cd | Cd (OH)2 (S) | NaOH (0.1 mol kg-1) |H2(1 atm) | Pt with Ecell = 0.0v at 298

K. If E°CD2+/Cd = -0.40V compute Ksp for Cd(OH)2.

Q3. (a) explain the principle underlying potentiometric titrations. elaborate the advantages potentiometric titrations?

(b) The standard free energy change for the reaction

H2(g, one atm) +1/2 O2 (g,11tm) ? H2O(l) is -237.19 kJ at 298 K.

i. Write the anodic and cathodic reactions if the reaction is to occur in a galvanic cell.
ii. Calculate the standard electrode potential for the electrodes

OH- | O2 | Pt and H+ | O2 | Pt
The cell potential producing the reaction

HO(l) = H+ (a=1) + OH- (a=1) is -0.8277V

Q4. (a) For the 1st order opposing reactions
k1
A ? B
?
k-1
with initial concentration of A and B as a and 0 respectively, show that the integral rate expression is provided by

ln (Xeq/ Xeq –X) = (k1 + k-1)t

where X is the concentration of B at time t and Xeq is that prevailing at equilibrium.

(b) The rate constant of a particular reaction is trebled on raising the temperature from 27°C to 37°C.What is the activation energy of this reaction ? At what temperature would its rate constant become 1 3rd of its value at 27°C?

Q5. (a) Derive expression for Langmuir adsorption isotherm. explain its limitations and suggest changes.
(b) The subsequent data were found for adsorption of acetic acid on charcoal

C/M 0.0181 0.0616 0.1259 0.2677 0.4711
x/m 0.457 0.801 1.11 1.55 2.04

Show graphically that the data fit into Freundlich adsorption isotherm and compute constants of the isotherm.

Q6. (a) (i) Show that half life period of nth order reaction is :

t1/2 = 2^n-1 -1 / (n-1)kn.ao^n-1


(ii) Show that t1/2 = ln A’ + Ea/RT
where A’ = 2^n-1-1/ A(n-1)ao^n-1 and A is the pre-exponential factor in Arrhenius formula.

(b) discuss briefly Van’t Hoiff’s differential method to obtain out the order of a reaction.


part B

Q7. (a) describe quantum yield. How is quantum yield determined experimentally?

(b) Formaldehyde can be synthesized by irradiating a mixture of CO and H2 containing a trace of Hg with light of wavelength 253.7 nm. Show that reaction mechanism
Iabs
Hg -----> Hg*
k2
Hg* + H2 -----> 2H + Hg

k3
H + CO -----> HCO
k4
HCO +H2----> HCHO + H
k5
2HCHO -----> HCHO + CO
k6
2HCO ----> CHO
|
CHO
confirms to the subsequent rate legal regulations :

d[HCHO]/dt = k5 Iabs/ (k5 + k6 ) + k4[H2] ( Iabs / k5 + k6 )^1/2

Q7. (a) Write the reaction mechanism suggested by Michaelis-Menten for enzyme catalysis ? Derive the expression for Michaelis-Menten formula for an enzyme catalysed reaction.

(b)Using the above formula determine the value of Michaelis constant from the subsequent data :

[S] ro
(substrate concentration) (initial rate)
mol/dm3 mol dm-3 sec-1

0.4 2.40
1.0 4.80
2.0 7.40
3.0 8.70
4.0 9.50
5.0 10.50


Q8. Write short notes on any 3 of the subsequent :

a) Glass electrode

b) Parallel Reactions

c) Photo chemical equilibrium

d) Physical adsorption and Chemisorption

Earning:   Approval pending.