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Flashcards

adsorption

sakhi rathore Chemistry class 12 English 58 cards

adsorption

Cards in this deck (58)

  1. 1what is surface chemistry?it deals with the phenomena that occur on the surface or boundary separating two bulk phases
  2. 2what is adsorption?the tendency of solids and liquids to attract molecules on their surface.
    EG ink on chalk
  3. 3what can be the reason of adsorption?at the surface of solids and liquids, they have residual vacancies, and to fulfill these vacancies they attract molecules towards them.
  4. 4what are adsorbate and adsorbent?adsorbate is the adsorbed species and adsorbent is something on which adsorption takes place.
  5. 5give some examples of adsorption.1)when gases like H2, O2 are taken in a container, and when powdered charcoal is added to it the pressure decreases.
    2) when the animal charcoal is added to methylene blue and shaken it loses its blue color.
  6. 6give some more examples of surface chemistry.3)raw sugar is not white but when passed through animal charcoal it is decolorized and white crystals are obtained.
    4) silica gels are used to preserve leather items as it adsorbes moisture.
  7. 7what is absorption?when a substance passes through the surface into the bulk and gets evenly distributed in the liquid or solid.
  8. 8give some examples of absorption.1)water vapor is absorbed by anhydrous CaCl2
    2)NH3 is absorbed by water to form NH4OH
  9. 9brief about adsorption1)it is a surface phenomenon
    2)conc. of substance is more at the surface than the bulk
    3)the rate of adsorption is initially faster the slows down when reaching equilibrium.
  10. 10brief about absorption1) it is a bulk phenomenon
    2)the substance is uniformly distributed throughout the bulk
    3) the rate of absorption remains the same throughout the process.
  11. 11what is sorptionin some cases, adsorption and absorption take place simultaneously.
    Eg dye applied to the fabric.
  12. 12what is occlusionit is adsorption of gases by metals
    Eg H2 by Pd
  13. 13what is negative adsorption?in some cases, the solvent from the solution may be adsorbed by the adsorbent such that the solution becomes more than the initial amount.
    Eg when dilute KCl solution is adsorbed on the surface of blood charcoal.
  14. 14what is desorption?removal of adsorbed substances from the surface by increasing temp. or decreasing pressure.
    used in physical adsorption.
  15. 15what is the thermodynamics of adsorption?adsorption is spontaneous process so delta G is negative also delta S is negative. so to make Delta G negative delta H also has to be negative.
  16. 16thermodynamics od adsorptionduring adsorption absorbate molecules are held trough weak v.w. forces or form true chemical bonds and in formation of bond some heat is released. hence delta H is negative and delta H is more than TdeltaS
  17. 17exceptions of chemical adsorption where heat is not released.1) adsorption of H2 on the glass surface is spontaneous and endothermic.
    2) adsorption of highly hydrated solutes on solid surface is also endothermic.
  18. 18what happens to thermodynamics of adsorption as the rate of adsorption decreases?as the rate of adsorption decreases delta H becomes less negative and finally equal to TdeltaS at equilibrium and delta G finally becomes equal to zero
  19. 19what are the types of adsorption?the types of adsorption are physisorption and chemisorption.
  20. 20what is physisorptionbond b/w the adsorbed and the adsorbent is weak Vanderwal forces.
  21. 21what is chemisorption?bond b/w the adsorbent and adsorbed is chemical.
  22. 22difference b/w physisorption and chemisorption. part 1P- the heat of adsorption is low about 20-40 KJ/mol
    C- the heat of adsorption is high about 80-240 KJ/mol
  23. 23difference b/w physisorption and chemisorption. part 2P- no compound formation takes place in these cases.
    C-surface compounds are formed in these.
  24. 24difference b/w physisorption and chemisorption. part 3P- the process is reversible
    C- the process is irreversible
  25. 25difference b/w physisorption and chemisorption. part 4P- does not require any activation energy.
    C- it requires activation energy.
  26. 26difference b/w physisorption and chemisorption. part 5P- this type of takes place at low temp. and decreases with increase of temp.
    C- this type increases with an increase in temp. this effect is called activated adsorption.
  27. 27difference b/w physisorption and chemisorption. part 6P- it is not specific in nature.
    C- it is specific in nature and occurs only when there is some possibility of compound formation.
  28. 28difference b/w physisorption and chemisorption. part 7P- the amount of gas absorbed is related to ease of liquification.
    C- there is no such correlation.
  29. 29difference b/w physisorption and chemisorption. part 8P- it forms a multilocular layer
    C- it forms a unilocular layer
  30. 30difference b/w physisorption and chemisorption. part 9P- increases with an increase in the surface area.
    C-also increases with an increase in surface area
  31. 31difference b/w physisorption and chemisorption. part 10both increase with the increase in surface area.
  32. 32the heat of adsorption.the amount of heat evolved when one mole of gas is adsorbed on the adsorbent.
  33. 33why is the case of N2 and Fe special?because it is a case where physisorption takes lace at low temp and chemisorption takes place at a higher temperature.
  34. 34physio and chemisorption graphs.physio and chemisorption graphs.
  35. 35how does nature and surface area of adsorbent effect the adsorption of gasessame gases are adsorbed to different extend by the different solids.
    surface ara increases adsorption increases.
    as particle size decreases adsorption increases.
  36. 36what is the specific surface area?the total surface area of 1 gm adsorbent.
  37. 37how does the nature of gases being adsorbed effect adsorption?critical temp. of a gas is the measure of it's Vanderwal forces and ease of attraction. extend of adsorption increases with increase in TC
    Tc=8a/27rb
    where a and b are v.w. forces of attraction and r is gas constant
  38. 38what is critical temp.?where gas can't be liquified further by applying pressure.
  39. 39at same temp. vol. of gases adsorbed by 1 gm charcoal at NTP followsH2 < N2 <
    CO < CH4 < CO2 < HCl < NH3 < SO2
  40. 40what is the effect of temp? on adsorptionat low temp. effect of pressure is more than at high temp.
  41. 41what is Freundlich adsorption isotherm?at a constant temp. how the extend of adsorption of a gas by solid is affected by pressure was shown by Freundlich in 1909.
  42. 42Freundlich adsorption isotherm numericallyx/m=kp^1/n where n>1and x/m is the quantity of gas adsorbed by a unit mass of solid adsorbent
  43. 43graph of FAIgraph of FAI
  44. 44what do the graphs of adsorption indicate?the graphs represent that at a fixed pressure x/m (physisorption) decreases with increase in temp.
  45. 45what is saturation pressure?the pressure above which the extend of adsorption becomes independent of pressure.
  46. 46what is adsorption isostere?for a given amount of adsorption of a adsorbate. the graph b/w P vs T is called isosterewhat is adsorption isostere?
  47. 47what were the limitations of Freundlich isotherms?a) gives only an approximate relationship
    b) works only for a limited range of pressure
    c) no mathematical derivation of x/m=k.p^1/n
    d) why x/m becomes independent of pressure at higher pressure was not explained.
  48. 48what is adsorption from the solution phase?solids can also adsorb solutes from solution.
    EG adsorption of acetic acid with charcoal conc.
    litmus solution is shaken with charcoal becomes colourless
    ppt of Mg(OH02 becomes blue when treated with magneson reagent as magneson is adsorbed on Mg(OH)2    what is adsorption from the solution phase?
  49. 49observations made in case of adsorption?the extend of adsorption depends on the conc. of solute in solution and nature of adsorbate and adsorbent.
  50. 50adsorption in preserving vacuumactivated charcoal is used in Dewar flasks to preserve the vacuum
  51. 51adsorption in gas masksall gas masks contain suitable adsorbent so that the poisonous gases are preferentially adsorbed.
  52. 52what is preferential adsorptiona strongly adsorbable substance can adsorb even by displacing the preadsorbed weak substance.
  53. 53adsorption in the decolorization processsugar passes over activated animal charcoal
  54. 54adsorption for making the moisture-free atmosphere.silica gel is used to remove moisture.
  55. 55adsorption in the separation of inert gasesnoble gases are separated by preferential adsorption on charcoal at diff. temp.
  56. 56adsorption in the purification of watercharcoal is used to remove impurities from water also ions are removed by using ion-exchange resins.
  57. 57adsorption in the extraction of metal.froth floatation process used for conc. of ores is based on preferential adsorption of ore particles.
  58. 58what are the adsorption indicators?some dyes like eosin get adsorbed on the surface of precipitates and this property is the basis for adsorption.

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class 12 Chemistry Flashcards on adsorption , created by sakhi rathore on 23/07/2020.
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sakhi rathore
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