5. surface chemistry (1)

8/13/2019 5. Surface Chemistry (1)

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a) 5h&sical adsorption (5h&sisorption). b) Chemical %dsorption. (Chemisorption).

#i""erence bet$een phsisorption !nd Chemisorptions

%hsisorption Chemisorption

*) It arises because of ander 6aals7forces.

2) It is not specific in nature.

#) It is reversible in nature

8) It depends on the nature of gas. 9ore easil&liquefiable gases are adsorbed readil&

:) ;nthalp& of adsorption is low (2


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In the above diagram (graph) at low pressure regionx

m 5*

%t high pressure regionx

m 5B. A sm!'' !mo+nt o" si'ic! &e' !nd ! sm!'' !mo+nt o" !nhdro+s c!'ci+m ch'oride !re

p'!ced sep!r!te' in t$o corners o" ! ,esse' cont!inin& $!ter ,!po+r. D. 0. The cond+ct!nce o" !n em+'sion incre!ses on !ddin& common s!'t.


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So'+tion:

=ell&. Cheese.

The name of this colloidal solution is gels.

>0B. P

#-

>0. -1. The e2tent o" phsic!' !dsorption decre!ses $ith rise in temper!t+re $h?

So'+tion :

i)The ph&sisorption shows the features of ph&sical process .%s ph&sisorption is generall&

e+othermic the e+tent of ph&sisorption decreases with rise in temperature.

ii) The ph&sisorption is due to weak wander wall bond between absorbent and adsorbate whichstarts breaking with rise in temperature.

>-0. Ho$ to prep!re co''oid!' so'+tion b chemic!' method?

So'+tion :

i) ouble decompositionK %s2O# E #!2$ %s2$# E #!2O

ii)O+idation K $O2 E !2$ #$ E 2!2O

iii)Leduction 2%uCl# E !C!O E #!2O 2%u E #!COO! E>!Cl

iv) !&drol&sisK 0eCl# E #!2O 0e(O!)# E#!Cl

>--.


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>-/. -. )i,e the "orm+'! o" 5SM;/.

So'+tion:

F$9-: stands for Feolite sieve of molecular porosit&-:it is aluminosilicate.

!+(%lO2)+($iO2)B>-+P.*>!2O

>@1. Under $h!t conditions ! mo'ec+'!r so'+tion becomes co''oid!' so'+tion?

So'+tion: i) If a molecular has less than *nm si3e is sub'ected to

Leduction. !&drol&sis O+idation double decomposition which leads to

association of moleculesatoms formed in this processes leads to formation

colloidal solution .

ii) If a (single) molecule it self has colloidal dimension then also molecular

solution becomes colloidal solution.

>@0. Ho$ $i'' o+ distin&+ish t$o tpes o" em+'sions oi' in $!ter K $!ter in oi'?

So'+tion:

*)&e testK % small amount of oil soluble d&e is added to it. i) if it is water in oil t&pe the background become colored. i) if it is oil in water t&pe colored droplets can

be seen.

2) ilution testK 6ater is added to the emulation i) If it is diluted b& water then it is oil in

water t&pe.ii) If it is not diluted b& water and forming two separate la&ers then it is oil in

water t&pe .

>@-. @.


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i) The ions carr&ing charge opposite to that of sol. 5articles are more effective in causing

coagulation of colloidal solution. These ions are called active ions.

ii) Coagulation power of electrol&te is directl& proportional to the valenc& of active ions

causing coagulation.

>@B. )i,e "o+r !pp'ic!tions o" co''oids?

So'+tion:

i) Lubber plating

ii) $ewage disposal

iii) In making disinfectants

iv) In making pharmaceutical preparations.

v) 0or purif&ing water.

vi) 0or precipitating carbon from smoke. ( Cottrell smoke precipitator)

vii) %rtificial rains.

viii) elta formation at the place where river 'oins with sea.

>@. Ho$ Cottre'' smo*e precipit!tor +se to p+ri" smo*e "rom co''oid!' p!rtic'es?

So'+tion:

6hen smoke is passed through Cottrell smoke precipitator the carbon particles get

discharged %nd precipitated b& appl&ing high voltage while smoke comes out of

chimne& of industrial plant.

>@D. 0. @. E2p'!in the modern !dsorption theor hetero&eneo+s c!t!'sis?

*


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So'+tion:

i) iffusion of reactant to the surface of catal&st.

ii) %dsorption of molecules of reactant at the active site.

iii) 0ormation of intermediate on the surface of catal&st.

iv) esorption of product molecules.

v) iffusion of products from the surface of catal&st and allowing new reactant molecules.

>. B. $h!t is e'ectro *inetic potenti!' or 5et! potenti!'?

So'+tion:

The potential difference between fi+ed la&er and diffused la&er of opposite charges is calledFeta potential.

>. The cond+ct!nce o" !n em+'sion b !ddin& common s!'t?


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CO E !2 !C!O>/0.Why the sun looks red at the time of setting? Explain on the basis of Colloidal

properties.

So'+tion:At the time of setting, the sun is at the horizon. The light emitted by the sun has to travela longer distance through the atmosphere. As a result, blue part of the light is scatteredaway by the dust particles in the atmosphere. Hence, the red part is visible.

Q52. "Ation of soap is due to emulsifiation and mielle formation".Comment.

So'+tion:

es action of soap is due to emulsification and micelle formation. $oaps are sodium salt of

higher fatt& acids like sodium stearate C*@!#:COO-"aE

Q5!.ifferentiate bet#een homogeneous and heterogeneous atalysis. $i%e oneexample for eah.

&olution'

(omogeneous atalysis:-A catalysis in which the catalysts are present in the same phaseas the reactants. For eample- oidation of !" gas with "#gas in the presence of $" gas ascatalyst.

(eterogeneous atalysis:-A catalysis in which a catalyst is present in different phase thanthat of the reactants. For eample- manufacture of ammonia from nitrogen and hydrogengases using solid iron as catalyst.

Q5). What are the important features of a solid atalyst?

&olution'The important features of a solid catalyst are: -

i% Activity: - &ts capacity to increase the speed of the chemical reaction.

ii% 'electivity: - &ts ability to direct the reaction to form particular products.iii% 'pecificity:-A given substance can act as a catalyst for a particular reaction only andnot for all reactions.

Q55. $i%e any four fators on #hih adsorption of a gas on a solid depend?

So'+tion:The factors on which the adsorption of a gas on a solid depends are:i% 'urface area of adsorbent :-Higher the surface area larger the adsorptionii% Temperature :-Adsorption of a gas decreases with increase in temperatureiii%5ressure :-At a constant temperature the adsorption increases with increase in pressure

iv% $ature of adsorbed gas :-(ifferent gases are adsorbed to different etents by the sameadsorbent

>/B. Compare the oagulating po#er of AlCl!#ith that of *aCl. $i%en that theiroagulation %alues are +.+,!+ and 52 respeti%ely.

So'+tion:As coagulating power is inversely proportional to coagulating value,Thus, Al!l)has **+ times greater coagulating power than $a!l.

Q5-.esribe the preparation of the follo#ing olloidal solution.a/ &il%er solb/ &ulphur sol

&olution'(a) 0reparation of &il%er sol' 1y the reduction of very dilute solution of silver salts with

a suitable reducing agent

*


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#Au!l) )'n!l#------------- #Au )'n!l/

0old sol

b/ 0reparation of &ulphur sol' 1y the oidation of H#' in the presence of suitableoidizing agent li1e nitric acid, bromine water, etc.

H#' r#-------------- ' #HrH#' #H$")------------ #H#" #$"# '

Q5. What is demulsifiation? *ame t#o demulsifiers.

So'+tion:The process of separation of the constituent li2uids of an emulsion is calleddemulsification. (emulsification can be done by centrifugation or boiling.

Q5,. $i%e any t#o reasons for the origin of eletrial harge on the olloidal partiles.&olution'The two reasons are:i% (ue to electron capture by sol particles during electro dispersion of metals, due topreferential adsorption of ions from solution

ii% (issociation of colloidal sols.33+. (o# is 4angmuir adsorption isotherm superior to reundlih adsorption

isotherm?

So'+tion:4angmuir adsorption isotherm is superior to Freundlich adsorption isotherm because

a% The results obtained from this isotherm are in better agreement with eperimentalvalues.

b% &t is applicable over a wider range of pressure.

Q36. (o# an a solid adsorbent be ati%ated?

So'+tion:A solid adsorbent can be activated by increasing the surface area of the adsorbent which

can be done by :-a%9a1ing the surface of the adsorbent rough

b%4y subdividing the adsorbent into smaller particlesc% 4y removing the gases already adsorbed

>B-. What are the steps in%ol%ed in the en7yme ataly7ed reations?

So'+tion:'teps involved in the enzyme catalyzed reactions are:-i% Formation of enzyme substrate comple.ii% (issociation of the enzyme substrate comple to form the products.

Q3!. What is the differene bet#een the lok1key model and the indued1fit model ofEn7yme ation?

So'+tion:&n loc1-1ey model the substrate fits into the already eisting active sites on the enzyme asa 1ey fits into a loc1. ut, in induced-fit model it5s the substrate that induces changes in

the active sites of the enzymes to adopt a perfect fit.

>B.What is emulsion? What are their different types?&olution'

An emulsion is the colloidal dispersion in which both the dispersed phase and thedispersion mediums are li2uids. They can be of two types:-i% 6mulsion of oil in water.ii% 6mulsion of water in oil.

Q35. What is emulsion? What are their different types?&olution'A catalyst lowers the activation energy for the forward as well as the bac1ward reaction.

As a result the reaction follows an alternate path by which the e2uilibrium is attained2uic1ly but the e2uilibrium constant remains unchanged.

Q33. ifferentiate bet#een eletrophoresis and eletro1osmosis?&olution'

*


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6lectrophoresis is the movement of colloidal particles under the influence of an electricalfield.

6lectro-osmosis is the movement of dispersion medium molecules under the influence ofelectric field when colloidal particles are not allowed to move.

Q3-. (o# an 8a9 : 8b9 be alulated for 4angmuir adsorption isotherm' x;m

5. surface chemistry (1)

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