Chapter-5
Surface Chemistry
Q1.Gelatine is generally added to ice creams. Why?
Ice cream is an emulsion of milk or cream in water (o/w type). Gelatine is
generally added to act as emulsifiers to form the stable emulsion.
Q2. Why is chemisorption called activated absorption?
For a chemisorption to take place ,reactants should acquire
minimum energy of activation.
Q3. Why is desorption necessary in catalytic reaction?
Desorption is necessary in catalytic reaction to maintain the flow of
reaction.
Q4. In chemical reaction can a product formed act as catalyst? If so
give example.
Yes, Example: hydrolysis of ester. Ester hydrolysis is catalysed by acid.
In the course of the reaction carboxylic acid is produced which catalyses
the reaction.
Q5. What is colloidion solution?
Colloidion solution is the solution which is used to impregnate the filter
paper to make it an ultra filter.
Q6. Give conditions for Tyndall effect to take place?
The refractive indices of dispersion medium & dispersed phase should
not be same. The wavelength of the light should not be too low.
Q7 Why is the ester hydrolysis slow in the beginning & becomes faster
after
sometime?
The ester hydrolysis slow in the beginning & becomes faster after
sometime
because the carboxylic acid produced acts as the catalyst.
Q8. What are the reasons for charge on sol particles?
Frictional electrification
Electron capture
Preferential adsorption of ions from solutions
Dissociation of surface molecules
Q9. Why colloidal medicines are more effective?
Colloidal medicines have large surface area for the reaction. Hence
colloidal medicines are more effective.
Q10.Give the factors governing colour of colloidal solution?
Wavelength of light scattered, the manner in which light is received by
observer, particles size.
Q11. Why are Lyophylic colloids self stabilized?
Due to the force of attraction between dispersion medium & dispersed
phase.
Q12. State one application ZSM-5.
Used for the conversion of alcohol to gasoline.
Q13. Explain the role of catalyst in a chemical reaction.
It lowers the activation energy & hence increases the rate of the reaction.
Q14. Adsorption is always exothermic. Why?
During adsorption, the bonding takes place between adsorbate &
adsorbent and there is a decrease in surface area & decrease in entropy.
Q15. Define weeping of gels. Give the other name of weeping?
When gels are allowed to stand for a long time they give out small
quantity of trapped liquid which accumulates on its surface. This action
of gels is called as weeping, other name is syneresis.
Q16. What is Thixotrophy?
Conversion of sol to gel is called thixotrophy.
Q17. Why is FeCl3 preferred over KCl for a cut leading to bleeding?
Fecl3 has more positive charge and causes coagulation of blood
quickly.
Q18. Why is silica gel used as dehumidifier?
Silica gel adsorpes moisture on its surface quickly.
Q19. Give the kinetics of adsorption of gases on metal surfaces.
Adsorption of gases on metal surfaces follows zero order kinetics.
Q20. G is negative for adsorption process. Why?
Adsorption is exothermic & decrease in entropy occurs in adsorption.
Q21. Give the significance of Brownian movement.
It gives stirring effect to the colloid. Hence colloidal particles do not
aggregate. The colloid becomes stable.
Q22. What happens when blood charcoal is shaken with conc. Kcl
in one case and its dilute KCl solution in other case?
In conc. KCl positive adsorption occurs & in dilute Kcl negative
adsorption occurs.
Q23.Give the principle used in gas masks?
Competing adsorption
Q24. Gold sol appears red , purple & also golden in colur Why?
Colour of the gold sol changes with its particle size.Its’ colour is red
& becomes puple when size increases & finally becomes golden.
Q25. Give the sign of ∆H & ∆S when Br2 gas gets adsorbed on charcoal.
∆H = negative & ∆S = positive
Q26. What is Argyrol?
Colloid of Ag with proteine(mild silver protein)
Antiseptic & used for treating gonoria (a disease)
Q27. What happens when NaCl is added to ferrichydroxide sol?
When NaCl is added to ferrichydroxide sol coagulation occurs.
Q28.Differentiate dilute soap solution & concentrated soap solution.
Dilute soap solution behaves like a true solution & concentrated soap
solution behaves like a colloid.
Q29. Comment: Colloid is not a substance but it is a state of a substance.
The nature of the sub whether colloid or crystalloid depends upon the
particle size.When the size of the solute particles lies between 1000 –
10000 pm , it behaves as a colloid & whenit is less than this value it
behaves as a crystalloid. Thus Colloid is not a substance but it is a state of
a substance which depeds upon the particle size.
Q30. What happens when Fe(OH)3 is added to Gold sol?Why?
The Gold sol is negatively charged, Fe(OH)3 is positively charged
& so coagulation occurs.Color of Gold sol changes from red to blue. Gold
sol changes from red to blue due to the change in the particle size.
(AS THIS CHAPTER HAS NO NUMERICALS HOTS MAY INCLUDE
THE QUESTIONS OF THE ABOVE TYPE)
Chapter-8
d and f block Elements
1. Silver atom has completely filled d orbitals in its ground state. How
can you say that it is a transition element?
Ans: It forms AgF2 a dark brown crystalline solid
2. Transition elements exhibit their highest oxidation state in their
oxides not in Flourides.Why?
Ans: Because oxygen can form covalent multiple bonds.
3. Explain why, Zn (II) salts are white while Mn (VII) are deep
purple in colour?
Ans: due to charge transfer between O2- ion to Mn7+
4. KMnO4 is used in acidic medium quite frequently than in its
aqueous or alkali for oxidizing purpose. Why?
Ans: In acidic medium MnO4- involves the addition of 5e- or Eo =
+1.52v
5.Inspite of low enthalpy of atomiza
6.Give reasons:
i) Zr and Hf have identical sizes
ii) In the titration of FeSO4 with KMnO4 in the acidic medium
dil.H2SO4 is used instead of dil HCl
Ans: i) Due to lanthanoid contraction
ii) dil.HCl is reducing agent and liberates chlorine on reacting with
KMnO4 soln.
7.Calculate the spin only magnetic moment of Iron present in the
following compound.
Fe(H20)5NO 2+
Ans: 5.92 BM
8. K2 PtCl6 is a well known compound whereas the corresponding
Ni compound is not known. State the reason for it.
Ans: The oxidation state of Pt in K2 PtCl6 is +4, which is a stable
oxidation state for Pt. The same oxidation state Ni is very difficult
because of (I.E1 + I.E 2+ I.E 3+I.E 4)
9. Among the ionic species Sc 3+ ,Ce 4+ and Eu2+ Which one is a good
oxidizing agent?
Ans: Ce 4+ is a good reducing agent because it can readily change to the
most stable oxidation state by gaining one electron. Others cannot do so.
10. Why are Fe 3+ and Cu 2+ prominent in their aqueous solutions?
Ans: Because of high hydration enthalpies.
11. There is a dip in the melting point curve at Mn, though the
preceding element also has similar electronic configuration. Why?
Ans: Due to 3d 5 half filled configuration which are tightly held by more
effective nuclear charge of Mn
12. CrO3 is an acid anhydride. Explain.
Ans: It dissolves in water to give chromic acid.
CrO3 + H2O
H2 CrO4
2+
13. Though both Cr and Mn 3+ have d4 configuration, yet Cr2+ is
reducing and Mn3+ is oxidizing. Explain Why?
Ans: Because of the stable half filled configuration of t2g sets Cr3+
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