surface chemistry Flashcards
what is activated charcoal?
on heating charcoal at a very high temperature, all the vapours get evaporated from the surface and the surface becomes porous
how does adding charcoal to organic dyes affect their colour?
they turn colourless
how does silica gel affect the moisture in air?
air gets dry
absorption is a _ phenomenon, while absorption is a _ phenomenon
bulk, surface
thermodynamical parameters with respect to adsorption
delta S, G, H are all negative
surface area increases/decreases with absorption
increases
highly liquifiable gases=> _ absorption
more
condition at which absorption is spontaneous
Delta H> T delta S
difference between physiorption and chemiosorption
.
why does physiorption result in multimolecular layers while chemiosoprtion results in unimolecular layers?
chem bonds can be formed only with one layer, which is in direct contact while in physiorption layers of gas can be adsorbed one over another
what does Freundlich adsorption isotherm represent?
variation in amt of gas adsorbed with pressure at constant temp.
relation between x, m, k, t for physiorption
x/m=k/t
freundlich equation in standard and log form
.
variation of extent of adsorption with pressure for different pressures
ease of liquification is _ to intermolecular forces
directly proportional
limiation of freundlich
not able to explain x/m at v high pressure
sols of water, alcohol, benzene are called
hydrosol/aquasol, alcosol, benzosom
lyophilic colloids are intrinsic of extrinsic
intrinsic
formation of lyophilic and lyophobics sols
philic- mixing larger molecules with suitable liq
phobic- mixing metlas/sulphides etc w suitable liqs
how can lyiphobic sols be coagulated easily
be adding small amt of electrolytes
what are micelles
particles that at specific low temp and CMC behave as electrolytes and behave as colloids at temp highter than TK
explain peptization
formation of colloidal.sol by converting ppt into it and shaking with dispersion medium in presence of electrolyte
for chemically preparing colloids, what processes can be used?
double decomposition, oxidation, reduction, hydrolysis
for chemically preparing colloids, what processes can be used?
double decomposition, oxidation, reduction, hydrolysis
bredigs arc method
electric arc is struck bw electrodes of metal immersed in diserpersipn medium, intense heat vapourizes the metal which then condenses to form particles of colloidal size
dialysis
seperating particles of colloid and electrolytes by diffusion through a suitable membrane
electrodialysis
making dialysis faster by applying an electric field if dissolved particles in impure colloid are electrolytes as ions present migrate out to opp charged electrodes
how to make ultra filter paper
soak filter paper in colloidal solution (4% of nitrocellulose in mix of alcohol and ether) and hardening by formaldehyde and drying it
theory of preferential adsorption
particles constituing the dispersed phase generally adsorb only those ions preferentially which are common with their own lattic ions
what is coagulation/pptn
aggregating colloid particlee to change them into large sized particles which later set as ppt
flocculating ion
when an elevtrolyte is afded to colloidal sol, particles of sol take up opp charger ions and neutralise.
the ion responsibilenfor neutralisation of charge is called flocculating ion
coagulation value
min amt of electrolytes (minimol) that must be added to one litre of a colloidal.solution for complete coagulation is called the coagulation value
coagulation powrr and value relation
inversely proportional
hardy schulz rule
greater valence of coagulating ion means greater coagulation power
gold number
measure of power of lyophilic colloids to stop coagulation
gold no and protection power relation
inverse proportional
2 features of solid catalysts
activity (depends on strength of chemiosorption), selectivity (ability to direct a reaction to yield particular products)
enzymes in yeast
invertase, zymase, maltase
enzyme in malt
disastase
enzyme in soyabean
urease
enzyme in stomach
pepsin
mechanism of enzyme catalysts
- binding of enzyme to substrat3 to form activated complex
- decomposition of activated complex to form product
catalysts haber process
molybdenum iron
ostwald process catalyst
platinised asbestos
contact process catalyst
platinised asbestos or V2O5
cleansing action of soap
micelle consists of hydrophobic hydrcarbon like central core. soap molecules form micelle around oil droplets such that hydrophobe part of stearate ions is in the oil droplet and hydrophobic part projects out of the grease droplet like bristles
helmholtz electrical double layer
combination of layers of opposite charge around colloidal particles. 1st layer is fixed 2nd is mobile (diffused layer)
In Haber’s process, hydrogen is obtained by reacting methane with steam in presence of NiO as catalyst. The process is known as steam reforming. Why is it necessary to remove CO when ammonia is obtained by Haber’s process?
Because CO formed acts as poison for the catalyst used
What is the role of desorption in the process of catalysis?
In the heterogeneous catalysis carried over metal surface, adsorbed reactant species combine to form the products. They have to be desorbed from the surface so that more the reactants may be accommodated on the surface of the catalyst. Therefore, desorption has a specific role to play in the process of catalysis
Why is it essential to wash a precipitate with water before estimating it quantitatively
Precipitates are generally formed in the ionic reactions. Some ions of the reactants may be adsorbed or may stick on the surface of the particles of the precipitate. These can be removed by washing the precipitate repeatedly with water. In case these ions are not removed, they may introduce some error in weighing when the precipitate is estimated quantitatively.
Why is it essential to wash a precipitate with water before estimating it quantitatively
Precipitates are generally formed in the ionic reactions. Some ions of the reactants may be adsorbed or may stick on the surface of the particles of the precipitate. These can be removed by washing the precipitate repeatedly with water. In case these ions are not removed, they may introduce some error in weighing when the precipitate is estimated quantitatively.
colloid formed by solid phase and gaseous medium
aerosol
colloid formed by liquid and liquid
emulsion
colloid formed. y liquid phase and solid medium
gel
gas phase and liquid medium colloid
foam
liquid phase and gaseous medium colloid
aerosol
What are the factors which influence the adsorption of a gas on a solid?
nature of adsorbate and adsorbent, surface area of adsorbent, activation of adsorbent, pressure, temperature
What do you understand by activation of adsorbent ? How is it achieved?
Activation of adsorbent implies increasing its adsorbing power. This is achieved by increasing the surface area and also the number of pores and vacant sites (active centres) per unit area. The activation can be achieved in a number of ways.
What role does adsorption play in heterogeneous catalysis?
In heterogenous catalysis, generally the reactants are gaseous whereas catalyst is a solid. The reactant molecules are adsorbed on the surface of the solid catalyst by physical adsorption or chemisorption. As a result, the concentration of the reactant molecules on the surface increases further leading to increase in rate of reaction. Alternatively, one of the reactant molecules undergoes fragmentation on the surface of the solid catalyst producing active species which react faster. The product molecules in either case have no affinity for the solid catalyst and are deadsorbed making the surface free for fresh adsorption.
Explain what is observed when :
(i) a beam of light is passed through colloidal sol
(ii) an electrolyte NaCl is added to ferric hydroxide sol
(iii) electric current is passed through a colloidal sol ?
- path of light and colloidal particles become visible due to tyndall effect.
- the positive charged sol particles of ferric oxide get their charge neutralised by interacting with negative chloride ions. as a result they get coagulated.
- colloidal particles move towards opposite charged electrode
how do emulsifiers stabilise emulsion
by reducing interfacial tension between two liquids forming the emulsion
in froth floatation(used for conc of sulphide ores), the role of adsorption is
adsorption of pine oil on sulphide particles
chemisorption is also called
activated adsorption
adsroption is an _ process
exo
adsroption is an _ process
exo
adsorption explains _ catalysis
heterogeneous
activity of enzymes is ineffective at _
high temp
catalyst used in oxdn of SO2 to So3
v2o5
zeolites depend on
pores, aperture and size of cavities
enzyme activity is max at
310 k
hair cream is an example of
emulsion
lyophilic colloids are stable due to
same charge on all colloidal particles, solvation of colloidal particles
gold sol is a _ colloid
multimolecular
smoke is a
solid dispersed in gas
H2 gas is adsorbed on charcoal to a very little extent because of
weak vdw forces and low critical temp
emulsion cannot be broken by
heating or adding emulsifying agents
haemoglobin is not a
negative charged sol
what is the promoter for Fe in habers process
Mo
zeolite catalyst in petroleum industry
ZSM 5
which enzyme converts starch into maltose
disastase
which enzyme converts starch into maltose
disastase
