Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

Chemistry (CBSE XII) > Surface Chemistry > Flashcards

Surface Chemistry Flashcards

You may prefer our related Brainscape-certified flashcards:
AP® Chemistry flashcards Periodic Table flashcards Chemistry 101 flashcards Organic Chemistry 101 flashcards
1
Q

What is surface chemistry? Give examples of such phenomena.

A

Surface chemistry deals with phenomena that occur at the surfaces or interfaces.
Eg. Corrosion, crystallization, dissolution, electrode processes

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

Why is there no interface between gases?

A

Due to complete miscibility

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

How are clean surfaces obtained and maintained in order to accomplish surface studies?

A

Under very high vacuum of the order 10^(-8) to 10^(-9) Pascal, ultra clean surfaces of metals can be obtained.
These materials with clean surfaces must be stored in vacuum otherwise they will be covered by molecules of the major components of air such as dioxygen and dinitrogen.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

What is adsorption? What are adsorbent and adsorbate?

A

The accumulation of molecular species at the surface rather than in the bulk of a solid or liquid is termed adsorption.
The molecular species or substance which concentrates/accumulated on the surface is termed ADSORBATE.
The material on the surface of which adsorption takes place is known as ADSORBENT.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

Give some examples of good absorbents.

A

Charcoal, silica gel, clay, colloids, metals in finely divided state, etc.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

What are sorption and desorption?

A

SORPTION -
When both absorption and adsorption take place simultaneously.

DESORPTION -
The process of removing an adsorbed substance from a surface on which it is adsorbed.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

What causes adsorption?

A

Inside the adsorbent, all the forces acting between the particles are mutually balanced but on the surface, the particles are not surrounded by atoms or molecules of their kind on all sides. Hence, they possess unbalanced or residual attractive forces which attract the adsorbate particles to its surface.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

What is the nature of entropy, enthalpy and Gibb’s energy for adsorption?

A

Adsorption is accompanied by decrease in both ΔH (enthalpy) and ΔS (entropy) i.e. the values are negative.

ΔG = ΔH - TΔS for spontaneous reaction.
For it to be a spontaneous reaction, ΔG must be negative. For this to happen, ΔH has to have sufficiently high negative value as -TΔS for adsorption is positive.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

How is state of equilibrium obtained in the process of adsorption?

A

As the adsorption proceeds, ΔH becomes less and less negative and ultimately ΔH becomes equal to -TΔS and ΔG becomes zero. At this state, equilibrium is obtained.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

What is physisorption? What are it’s characteristics?

A

If accumulation of gas on the surface of a solid occurs on account of weak van der waal’s forces, the adsorption is termed as physisorption. Physisorption at low temperature may pass into chemisorption as the temperature is increased.
Characteristics -
1. Lack of specificity
2. Reversible nature
3. Extent of physisorption increases with increase in surface area of adsorbent
4. Enthalpy of adsorption is quite low (20-40 kJ/mol)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

How does physisorption depend on nature of adsorbate?

A

In general, easily liquefiable gases (higher critical temperatures) are readily adsorbed as van der waal’s forces are stronger near the critical temperatures.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

What is chemisorption? What are it’s characteristics?

A

When the gas molecules or atoms are held to the solid surface by chemical bonds (covalent or ionic), the adsorption is termed chemisorption.
Characteristics -
1. High specificity
2. Irriversible nature
3. Extent of chemisorption also increases with increase in surface area of adsorbent.
4. High enthalpy of adsorption (80-240 kJ/mol) as it involves chemical bond formation.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

What is adsorption isotherm?

A

Freundlich’s adsorption isotherm is an empirical relationship between the quantity of gas adsorbed by unit mass of solid adsorbent and pressure at a particular temperature.
x/m = k.p^(1/n) where n > 1

It explains the behaviour of adsorption in an approximate manner.
These curves indicate that at a fixed pressure, there is a decrease in physical adsorption with increase in temperature. It seems that saturation occurs at high pressure.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

What is the equation if instead of pressure, concentration is taken into account in Freundlich’s equation?

A

x/m = kC^(1/n)

where C is the equilibrium concentration (i.e. when adsorption is complete)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

What are some applications of adsorption?

A
  1. Production of high vacuum
  2. Gas masks
  3. Control of humidity
  4. Removal of colouring matter from solutions
  5. Heterogenous catalysis
  6. Separation of inert gases
  7. Curing diseases
  8. Froth floatation process
  9. Adsorption indicators
  10. Chromatiographic analysis
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

What are the slope & intercept for Freundlich adsorption isotherm?`

A

Slope = 1/n

Intercept = Log K

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

What are colloids? What is the range of diameters for their particles?

A

A colloid is a heterogenous system in which one substance is dispersed (dispersed phase) as very fine particles in another substance (dispersion medium).

The range of diameters is between 1 and 1000 nm
[ 10^(-9) to 10^(-6) m ]

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
18
Q

What are the 8 types of colloidal systems?

A 
Solid/Solid = Solid sol (coloured glasses, gem stones)
Solid/Liquid = Sol (paints, call fluids)
Solid/Gas = Aerosol (smoke, dust)
Liquid/Solid = Gel (cheese, jelly)
Liquid/Liquid = Emulsion (milk, butter, hair cream)
Liquid/Gas = Aerosol (fog, mist, cloud, insecticide spray)
Gas/Solid = Solid sol (pumice stone, foam rubber)
Gas/Liquid = Foam (froth, whipped cream, soap lather)
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
19
Q
  1. What are hydrosols/aquasols?

2. What are alcosols?

A
  1. If the disersion medium is water, the sol is called aquasol/hydrosol.
  2. If the dispersion medium is alcohol, the sol is called alcosol.
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
20
Q

Classify colloids based on interactuin between dispersed phase and dispersion medium.

A
  1. Lyophilic (solvent attracting) colloids -
    aka reversible sols because it can be reconstituted by simply remixing DP with DM.
    Eg. gum, gelatine, starch, rubber, etc.
  2. Lyophobic (solvent repelling) colloids -
    aka irriversible sols because they can be prepared and reconstituted only by special methods. They need stabilising agents for their preservation.
    Eg. metals and their sulphide, etc.
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
21
Q

Classify colloids based on the type of particles of the dispersed phase.

A
  1. Multimolecular colloids -
    On dissolution, a large number of atoms or smaller molecules of a substance aggregate together to form species having size in colloidal range.
    Eg. gold sol. sulpher sol
  2. Macromolecular colloids -
    They are molecules which have sizes that lie in the colloidal range.
    Eg. polymers like rubber, nylon, starch.
  3. Associated colloids (Micelles) -
    At low temperatures they behave as normal strong electrolytes but at higher concentrations they exhibit colloidal behaviour due to formation of aggregates. These micelles may contain as many as 100 molecules or more.
    Eg. soaps, synthetic detergents
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
22
Q

What are the thresholds above which micelle formation take place?

A

The formation only takes place above a particular temperature called KRAFT TEMPERATURE and above a particular concentration called CRITICAL MICELLE CONCENTRATION (CMC).

23
Q

Write a short note in mechanism of micelle formation.

A

Micelles are formed by association of such molecules in which both lyophilic and lyophobic parts are present. Such molecules are called surface active molecules. Example -
Soap is sodium or potassium salt of a higher fatty acid and may be represented as RCOONa (e.g.,
sodium stearate CH 3(CH2)16COO–Na+, which is a major component of many bar soaps). When dissolved in water, it dissociates into RCOO– and Na+ ions.
The RCOO– ions, however, consist of two parts — a long hydrocarbon chain R (also called non-polar ‘tail’) which is hydrophobic (water repelling), and a polar group COO– (also called polar-ionic ‘head’), which is hydrophilic (water loving).
The RCOO– ions are, therefore, present on the surface with their COO– groups in water and the hydrocarbon chains (R) staying away from it and
remain at the surface. But at CMC, the anions are pulled into the bulk of the solution and aggregate to form a spherical shape with their hydrocarbon chains pointing towards the centre of the sphere & COO– part remaining outward on the surface of the sphere. The aggregate thus formed is known as ‘ ionic
micelle’

24
Q

Write a short note on cleansing action of soap.

A

The cleansing action of soap is due to the
fact that soap molecules form micelle around
the oil droplet in such a way that hydrophobic
part of the stearate ions is in the oil droplet and
hydrophilic part projects out of the grease
droplet like the bristles. Since the polar
groups can interact with water, the oil droplet
surrounded by stearate ions is now pulled in
water and removed from the dirty surface. Thus
soap helps in emulsification and washing away
of oils and fats.

25
Q

How are colloids prepared by chemical methods?

A

Colloids can be prepared by chemical methods such as double decomposition, oxidation, reduction and hydrolysis.

Double decomposition :
As2O3 + 3H2S —-> As2S3 (sol) + 3H2O

Oxidation :
SO2 + 2H2S —-> 3S (sol) + 2H20

Reduction :
2AuCl3 +3HCHO + 3H2O —-> 2Au (sol) + 3HCOOH + 6HCl

Hydrolysis :
FeCl3 + 3H2O —-> Fe(OH)3 (sol) + 3HCl

26
Q

Write a short note in Bredig’s Arc method.`

A

This process involves dispersion as well as condensation. Colloidal sols of metals such as gold, silver, platinum, etc., can be prepared by this method.
In this method, electric arc is struck between electrodes of the metal immersed in the dispersion medium. The intense heat
produced vapourises the metal, which then condenses to form particles of colloidal size.

27
Q

What is peptization?

A

Peptization may be defined as the process of converting a precipitate into colloidal sol by shaking it with dispersion medium in the presence of a small amount of electrolyte. The electrolyte used for this purpose is called peptizing agent.
During peptization, the precipitate adsorbs one of the ions of the electrolyte on its surface. This causes the development of positive or negative charge on precipitates, which ultimately break up into smaller particles of the size of a colloid.

28
Q

What is purification of colloidal solution? Why are colloidal solutions purified?

A

The process used for reducing the amount of impurities to a requisite minimum is known as purification of colloidal solution .
While the presence of traces of electrolyte is essential for the stability of the colloidal solution, larger quantities coagulate it. It is, therefore, necessary to reduce the concentration of these soluble impurities to a requisite minimum.

29
Q

What is dialysis?

A

It is the process of removing a dissolved substance from a colloidal solution by means of diffusion through a suitable membrane.
The apparatus used for this purpose is called
dialyser. A bag of suitable membrane containing the
colloidal solution is suspended in a vessel through
which fresh water is continuously flowing.
The molecules and ions diffuse through membrane into
the outer water and pure colloidal solution is left behin

30
Q

How can the process of dialysis be sped up?

A

It can be made faster by applying an electric field if the dissolved substance in the impure colloidal solution is only an electrolyte. The process is then named ELECTRODIALYSIS.
The colloidal solution is placed in a bag of suitable membrane while pure water is taken outside. Electrodes are fitted in the compartment. The ions present in the colloidal solution migrate out to the oppositely charged electrodes.

31
Q

What is ultrafiltration and how can it be sped up?

A

Ultrafiltration is the process of separating the colloidal particles from the solvent and soluble solutes present in the colloidal solution by specially prepared filters, which are permeable to all substances except the colloidal particles.
To speed up the process, pressure or suction is applied.

32
Q

What is collodion solution? What is it’s composition?

How is ultra-filter paper prepared?

A

Pores of filter paper can be reduced in size by impregnating with collodian solution to stop the flow of colloidal particles.
The usual collodian is a 4% solution of nitro-cellulose in a mixture of alcohol and ether.

An ultra-filter paper may be prepared by soaking the filter paper in a collodion solution, hardening by formaldehyde and then finally drying it.

33
Q

What are the optical properties exhibited by colloidal solutions?

A
  1. Tyndall effect -
    The Tyndall effect is due to the fact that colloidal particles scatter light in all directions in space. This scattering of light illuminates the path of beam in the colloidal dispersion.
  2. Brownian movement -
    When colloidal solutions are viewed under
    a powerful ultramicroscope, the colloidal particles appear to be ina state of continuous zig-zag motion all over the field of view. This motion is independent of the nature of the colloid but depends onthe size of the particles and viscosity of the solution. Smaller the size and lesser the viscosity, faster is the motion.
  3. Colour -
    The colour of colloidal solution depends on the wavelength
    of light scattered by the dispersed particles. The wavelength of light further depends on the size and nature of the particles. The colour of colloidal solution also changes with the manner in which the observer receives the light.
    Eg. a mixture of milk and water appears blue when viewed by the reflected light and red when viewed by the transmitted light. Finest gold sol is red in colour; as the size of particles increases, it appears purple, then blue and finally golden.
34
Q

What are the 2 conditions required for Tyndall effect to occur?

A

(i) The diameter of the dispersed particles is not much smaller than the wavelength of the light used
(ii) The refractive indices of the dispersed phase and the dispersion medium differ greatly in magnitude.

35
Q

Write about the colligative properties of colloidal solutions.

A

Colloidal particles being bigger aggregates, the number of particles in a colloidal solution is comparatively small as compared to a true solution. Hence, the values of colligative properties (osmotic pressure, lowering in vapour pressure, depression in freezing point and elevation in boiling point) are of small order as compared to values shown by true solutions at same concentrations.

36
Q

Write about charge on colloidal particles.

A

Colloidal particles always carry an electric charge. The nature of this charge is the same on all the particles in a given colloidal solution and may be either positive or negative.
The presence of equal and similar charges on colloidal particles is largely responsible in providing stability to the colloidal solution, because the repulsive forces between charged particles having same charge prevent them from coalescing or aggregating when they come closer to one another.

37
Q

What causes the charge on sol particles?

A

The following are some reasons :

  1. Due to electron capture by sol particles during electrodispersion of metals
  2. Due to preferential adsorption of ions from solution
  3. Due to formulation of electrical double layer
38
Q

What is zeta potential?

A

Potential difference between the fixed layer and the diffused layer of opposite charges is called the electrokinetic potential or zeta potential .

39
Q

What is electrophoresis?

What is electroosmosis?

A

The movement of colloidal particles under an applied electric potential is called ELECTROPHORESIS. Positively charged particles move towards the cathode while negatively charged particles move towards the anode.

When electrophoresis, i.e., movement of particles is
prevented by some suitable means, it is observed that
the dispersion medium begins to move in an electric
field. This phenomenon is termed ELECTROOSMOSIS.

40
Q
  1. What is coagulation?
  2. What is coagulating ion?
  3. What is coagulation value?
A
  1. The process of settling of colloidal particles is called coagulation or precipitation of the sol.
  2. The ion responsible for neutralisation of charge on the particle is called the coagulating ion.
  3. The minimum concentration of a electrolyte in millimoles per litre required to cause precipitation of a sol in two hours is callled coagulating value.
41
Q

How can lyophobic sols be coagulated?

A
  1. By electrophoresis
  2. By mixing 2 oppositely charged sols (mutual coagulation)
  3. By boiling
  4. By persistent dialysis
  5. By addition of electrolytes
42
Q

What is the Hardy-Schulze rule?

A

Coagulation power is directly proportional to charge on ion.

Coagulation power is inversely proportional to coagulating value.

43
Q

How can lyophilic sols be coagulated?

A

The two factors which are responsible for the stability of lyophilic sols are the charge and solvation of the colloidal particles. When these two factors are removed, a lyophilic sol can be coagulated.
This is done (i) by adding an electrolyte and (ii) by adding a suitable solvent. When solvents such as alcohol and acetone are added to hydrophilic sols, the dehydration of dispersed phase occurs. Under this condition, a small quantity of electrolyte can bring about coagulation.

44
Q

What are protective colloids?

A

Lyophilic colloids have a unique property of protecting lyophobic colloids. When a lyophilic sol is added to the lyophobic sol, the lyophilic particles form a layer around lyophobic particles and thus protect the latter from electrolytes. Lyophilic colloids used for this purpose are called protective colloids.

45
Q

What are emulsions? What are the two types of emulsions?

A

Emulsions are the liquid - liquid colloidal systems i.e. the dispersion of finely divided droplets in another liquid.

The two types of emulsions are :
1. Oil dispersed in water (O/W type)
Eg. Milk, vanishing cream

  1. Water dispersed in oil (W/O type)
    Eg. Butter, cream
46
Q

What are emulsifying agents? List some.

A

For stabilisation of an emulsion, a third component called emulsifying agent is usually added. The emulsifying agent forms an interfacial film between suspended particles and the medium.
The principal emulsifying agents for O/W emulsions are
proteins, gums, natural and synthetic soaps, etc.
and for W/O, heavy metal salts of fatty acids, long chain alcohols, lampblack, etc.

47
Q

How can emulsions be broken into constituent liquids?

A

Emulsions can be broken into constituent liquids by heating, freezing, centrifuging, etc.

48
Q

What are some examples of colloids in daily life?

A
  1. Blue colour of the sky
  2. Fog, mist and rain
  3. Food articles
  4. Blood
  5. Soils
  6. Formation of delta
49
Q

What are some applications of colloids?

A
  1. Electrical precipitation of smoke
  2. Purification of drinking water
  3. Medicines
  4. Tanning
  5. Cleansing action of soaps & detergents
  6. Photographic plates & films
  7. Rubber industry
  8. Industrial products
50
Q

Why are meds more effective in colloidal form?

A

Colloidal medicines are more effective because they have

large surface area and are therefore easily assimilated.

51
Q

What is tanning?

A

Animal hides are colloidal in nature. When a hide, which
has positively charged particles, is soaked in tannin, which contains negatively charged colloidal particles, mutual coagulation takes place. This results in the hardening of leather. This process is termed as tanning. Chromium salts are also used in place of tannin.

52
Q

Write a short note on Cottrel smoke precipitator.

A

The smoke, before it comes out from the chimney, is led through a chamber containing plates having a charge opposite to that carried by smoke particles. The particles on coming in contact with these plates lose their charge and get precipitated. The particles thus settle down on the floor of the chamber. The precipitator is called Cottrell precipitator

53
Q

Give examples of naturally occuring as well as man-made macromolecules.

A

Naturally occuring -
starch, cellulose, proteins, enzymes

Man made -
polythene, nylon, polystyrene, synthetic rubber

Chemistry (CBSE XII) (2 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2024 Bold Learning Solutions. Terms and Conditions