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CHEM 23 > TITRIMETRY > Flashcards

TITRIMETRY Flashcards

1
Q

analytical procedures in which the amount of analyte is determined from the amount of standard reagent required to react with the analyte completely

A

titrimetric methods

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2
Q

types of titrimetric methods

A
  1. Volumetric method
  2. weight or gravimetric titrimetry
  3. coulometric titrimetry
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3
Q

type of titrimetric method where it is based on the volume of reagent of known concentration that is consumed by the analyte

A

volumetric method

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4
Q

type of titrimetric method where the mass of the titrant is measured rather than the volume

A

weight or gravimetric titrimetry

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5
Q

type of titrimetric method where the “reagent” is a constant direct current of known magnitude that reacts with the analyte; the time required to complete the reaction is measured

A

coulometric titrimetry

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6
Q

reagent of known concentration that is used to carry out a volumetric analysis

A

standard solution

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7
Q

performed by slowly adding a standard solution from a buret or other volumetric measurement device to a solution of analyte until the reaction between the two is complete

A

titration

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8
Q

final - initial = ?

A

volume needed

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9
Q

point of titration when the amount of added standard reagent exactly equals the amount of analyte

A

equivalence point

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10
Q

point in the titration where there is a physical change associated with the condition of equivalence

A

end point

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11
Q

often added to the analyte solution in order to give an observable physical change at or near the equivalence point

A

indicator

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12
Q

types of indicator

A

visual and instrumental

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13
Q

type of indicator where it changes in color at the equivalence point

A

visual indicators

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14
Q

type of indicator where it responds to certain properties of the solution during titration

A

instrumental indicator

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15
Q

determines the amount of excess standard titrant to be added

A

back titration

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16
Q

highly purified compound that serves as a reference material in all volumetric method

A

primary standard

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17
Q

use to prepare standard solution

A

primary standard

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18
Q

requirements for a primary standard

A
  1. high purity
  2. stable in air
  3. absence of hydrate water
  4. readily available at modest cost
  5. reasonable solubility in the titration medium
  6. reasonably large formula weight
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19
Q

methods to prepare standard solutions

A
  1. direct method
  2. standardized by titration (weighted quantity of primary standard and measured volume of another standard solution)
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20
Q

standard acids

A

HCl, HClO4, H2SO4

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21
Q

oxidizing acid

A

HNO3

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22
Q

standard base

A

NaOH, KOH, Ba(OH)2

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23
Q

phenolphthalein indicator color

A

• acid - colorless
• base - pink

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24
Q

methyl orange and methyl red

A

• acid - red
• base - yellow

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25
Q

bromothymol blue

A

• acid - yellow
• base - blue

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26
Q

indigo carmine

A

• acid - blue
• base - blue/yellow

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27
Q

primary standard are weighed and diluted to an exact volume of solution

A

direct method

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28
Q

best method to prepare standard solution

A

direct method

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29
Q

variables that influence behavior of indicators

A
  1. temperature
  2. ionic strength of the medium
  3. presence of organic solvent
  4. colloidal particles
30
Q

solubility rules

A
  1. all nitrates are soluble (NO3-)
  2. all chlorides are soluble except AgCl, Hg2Cl2, and PbCl2
  3. All sulfates are soluble except CaSO4, SrSO4, BaSO4, Hg2SO4, PbSO4, and Ag2SO4
  4. All carbonates are insoluble except the 1A elements and NH4-
  5. All hydroxides are insoluble except those of the 1A elements, Sr(OH)2, and Ba(OH)2; Ca(OH)2 is slightly insoluble
  6. all sulfides are insoluble except those of the 1A and 11A elements and NH4
31
Q

ways of expressing solubility

A
  1. molar solubility - no. of moles of solute dissolved in 1L of saturated solution
  2. solubility - number of grams of solute in 1L of saturated solution
32
Q

factors affecting solubility

A
  1. temperature
  2. presence of common and uncommon ion
  3. pH
  4. effect of complexing agent
33
Q

particle size

A
  1. crystalline suspension
  2. colloidal suspension
34
Q

particle size have dimension on the order of tenths of s millimeter or greater

A

crystalline suspension

35
Q

tend to settle spontaneously and are readily filtered

A

crystalline suspension

36
Q

tiny particles are invisible to the naked eye

A

colloidal suspension

37
Q

show no tendency to settle from solution nor are they easily filtered

A

colloidal suspension

38
Q

particle size is influenced by experimental variables such as

A

precipitate solubility, temperature, reactant. concentration, and the rate at which reactants are mixed

39
Q

the net effect of these variables could accounted by a single property called

A

relative supersaturation (RSS)

40
Q

if the RSS value is large, the precipitate is a ….

A

colloidal

41
Q

if the RSS value is small, the precipitate is…

A

crystalline solid

42
Q

in this process, large number of colloidal precipitate

A

nucleation

43
Q

higher rate of nucleation happens when

A

there is higher RSS

44
Q

this precipitation process happens when there is only smaller number of larger size particles appear

A

particle growth

45
Q

the rate of particle growth depends on..

A

RSS

46
Q

this determines the charge on a colloidal particle formed in gravimetric analysis

A

change of the lattice ion that is in excess when the precipitation is complete

47
Q

can be hastened by heating, stirring, and adding an electrolyte to the medium

A

coagulation

48
Q

a phenomena in which otherwise soluble compounds are removed from solution during precipitate formation

A

co-precipitation

49
Q

types of co-precipitation

A
  1. surface absorption
  2. mixed-crystal formation
  3. occlusion
  4. mechanical entrapment
50
Q

occurs when the precipitate has a large surface area

A

surface absorption

51
Q

a contaminant ion replace analyte ion in its crystal lattice (inclusion)

A

mixed - crystal formation

52
Q

compounds are trapped within a pocket during rapid crystal growth

A

occlusion

53
Q

a portion of solution are trapped when crystals are fused together

A

mechanical entrapment

54
Q

an important and widely used titrimetric reagent

A

silver nitrate (AgNO3)

55
Q

employed for the determination of anions that precipitates as silver salts

A
  1. halides
  2. halide like ions
  3. mercaptan and certain fatty acids
56
Q

halides

A

I-, Cl-, Br-

57
Q

halide like ions

A

SCN-, CN-, CNO-

58
Q

factor affecting end point sharpness

A
  1. reagent concentration
  2. end point improves as the analytical reaction becomes more complete
  3. the lower the value of Ksp the better will be the detection of the end point
59
Q

end point improves as solution concentration become more concentration

A

reagent concentration

60
Q

types pf argentometric titrations

A
  1. direct titration
  2. indirect “back” titration
61
Q

the analyte solution is directly titrated against standard AgNO3 solution

A

direct titration

62
Q

known excess of standard AgNO3 is added to the analyte solution

A

indirect “back” titration

63
Q

what happens during back titration

A

the excess unconsumed of standard AgNO3 is back titrated against another standard titrant

64
Q

types of direct titration

A
  1. Mohr method
  2. Fajan method
65
Q

titration technique that determines the concentration of chloride ions in a solution by using silver nitrate as a standard solution

A

mohr method

66
Q

limitations of mohr method

A
  1. the pH of the medium must be from 6-10
  2. In alkaline medium: Ag+ will precipitate as oxide
  3. this will interfere with the titration due to pptn of Ag2O before Ag2CrO2 where Ksp (Ag2O) < Ksp (Ag2CrO2) (+ve error)
  4. in the presence of ammonium salts, the pH must not exceed 8, free NH4 is released which dissolves AgCl ppt
  5. interfering ions (cations which give insoluble CrO4²- salts must be absent and anions such as AsO4²-, CO3²-, and PO4³- interfere by forming insoluble Ag salts in neutral or alkaline solutions
67
Q

the end point is detected by using absorption indicators that is absorbed on the surface of the precipitate immediately after the equivalence point

A

fajan method

68
Q

limitations of Fajans method

A
  1. coagulation of the precipitate must avoid sharp endpoint if surface area is large (increase absorption of indicator) — dextrine (protective coolloid) keep the ppt highly dispersed
  2. absorption indicators enhance the tendency of silver halides toward photodecomposition, which blackens the ppt — titration must be done rapidly in subdued light
  3. the titration solution must he controlled to ensure the indicator will exist in its ionized form — fluorescein (pKa = 7) operates in solution of pH 7 or more
69
Q

formation of soluble coloured complex

A

volhard method

70
Q

could be used for direct determination if Ag+ and indirect determination of halides and anions

A

volhard method

CHEM 23 (7 decks)

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