1. Titrimetric analysis. Acid–Base titration.
L e c t u r e 6
Titrimetric analysis. Acid–Base titration.
Associate prof . L.V. Vronska
Associate prof . M.M. Mykhalkiv

2. Outline
Titrimetric method of the analysis: the basic concepts and classification.
Technics of titrimetric analysis.
Types of titrimetric determinations.
Calculations in titrimetric analysis.
Protolytometry or acid–base titration (a neutralization method): the basic concepts, titrants, defined substances.
Indicator choice, calculation of errors of titration in a method protolytometry.
Nonaqueous acid–base titration.

3. 1. Titrimetric method of the analysis: the basic concepts and classification.
Titrimetry - any method in which volume is the signal.
Titrimetry, in which we measure the volume of a reagent reacting stoichiometrically with the analyte.

4. Titration setup: the titrant drops from the burette into the analyte solution in the flask. An indicator present then changes color permanently at the endpoint.

5. Titration of an acid solution of unknown concentration with a base solution of known concentration

6. Titration is a procedure for determining the concentration of a solution by allowing a carefully measured volume to react with a standard solution of another substance, whose concentration is known.
Standardization is the process of establishing a technical standard
In chemistry, an aliquot is usually a portion of a total amount of a solution.

7. Titrant - the reagent added to a solution containing the analyte and whose volume is the signal.
A reagent, called the titrant, of known concentration (a standard solution) and volume is used to react with a solution of the analyte, whose concentration is not known.
equivalence point - the point in a titration where stoichiometrically equivalent amounts of analyte and titrant react.

8. End point - the point in a titration where we stop adding titrant.
Indicator - a colored compound whose change in color signals the end point of a titration.
Titration error - the determinate error in a titration due to the difference between the end point and the equivalence point.
A primary standard is a standard that is accurate enough that it is not calibrated by or subordinate to other standards. A primary standard in chemistry is a reliable, readily quantified substance.

9. Secondary reagent - a reagent whose purity must be established relative to a primary reagent
A burette (also buret) is a vertical cylindrical piece of laboratory glassware with a volumetric graduation on its full length and a precision tap, or stopcock, on the bottom (or calibrated glass tube).
Even the thickness of the lines printed on the burette matters; the bottom of the meniscus of the liquid should be touching the top of the line you wish to measure from.

10. stopcock buret

11. Buret with bottle of standard solution
Gay-Lussac burette

12. Buret with rubber shutter
Mohr burette

13. Microburet:
а) Shilov air-powered Buret; б) stopcock buret

14. A pipette (also called a pipet, pipettor or chemical dropper) is a laboratory instrument used to transport a measured volume of liquid

15. Erlenmeyer flask or conical flask.

16. There are different ways of preparation of standard solutions:
on accurately weighed sample (primary standard)
by means of standard substance or a standard solution (secondary standard)
“standard titrimetric substance” (primary standard)

17. Accurately weighed sample (primary standard)
Because a volumetric flask contains a solution, it is useful in preparing solutions with exact concentrations. The reagent (the accurately weighed sample) is transferred to the volumetric flask, and enough solvent is added to dissolve the reagent. After the reagent is dissolved, additional solvent is added in several portions, mixing the solution after each addition. The final adjustment of volume to the flask’s calibration mark is made using a dropping pipet. To complete the mixing process, the volumetric flask should be inverted at least ten times.

18. Volumetric flask
Volumetric flask — for preparing liquids with volumes of high precision. It is a flask with an approximately pear-shaped body and a long neck with a circumferential fill line.

19. Proper means of reading the meniscus on a volumetric flask or pipet.
When filling a pipet or volumetric flask, set the liquid’s level exactly at the calibration mark. The liquid’s top surface is curved into a meniscus, the bottom of which should be exactly even with the glassware’s calibration mark. The meniscus should be adjusted with the calibration mark at eye level to avoid parallax errors.

20. Calculate concentration of primary standard

21. by means of standard substance or a standard solution (secondary standard)
secondary reagent - a reagent whose purity must be established relative to a primary reagent
To prepare the solution we place calculated amount of substance, weighed to the nearest tenth of a gram, in a bottle or beaker and add approximately volume of water

22. Establishment of secondary standard concentration
А) a measured volume of another primary standard solution
where:
CN2 and V2 are concentration and volume of secondary standard solution
CN1 and V1 are concentration and volume of primary standard solution

23. B) a weighed quantity of a primary standard
where:
CN and V are concentration and volume of secondary standard solution
m and Em are mass and equivalent weight of primary standard

24. Typical instrumentation for performing an automatic titration
Typical instrumentation for performing an automatic titration. Courtesy of Fisher Scientific.

25. Features of a primary standard include:
1. It should have crystal structure and correspond the chemical formula
2. High purity (it is the absence of impurity in a substance)
3. Stability (low reactivity)
4. Low hygroscopicity (it is the ability of a substance to attract water molecules from the surrounding environment through either absorption or adsorption) and efflorescence (in chemistry, is the loss of water (or a solvent) of crystallization from a hydrated or solvated salt to the atmosphere on exposure to air).

26. 5. High solubility (if used in titration)
6. High equivalent weight.
7. Not to contain extraneous impurity more than admissible borders for substances of mark “chemically pure”.
8. Methods of purification of standard substance from impurity (crystallisation, extraction, sublimation etc.) should be available in analytical laboratory.

27. Some examples of primary standards according to the European Pharmacopoeia 5, ch. 4.2:
Arsenic trioxide for making sodium arsenite solution for standardisation of sodium periodate solution (also for iodine and cerium (IV) sulfate solutions, since 2002 standardised by sodium thiosulfate)
Benzoic acid for standardisation of waterless basic solutions: ethanolic sodium and potassium hydroxide, TBAH, and alkali methanolates in methanol, isopropanol, or DMF
Potassium bromate (KBrO3) for standardisation of sodium thiosulfate solutions

28. Potassium hydrogen phthalate (usually called KHP) for standardisation of aqueous base and perchloric acid in acetic acid solutions
Sodium carbonate for standardisation of aqueous acids: hydrochloric, sulfuric acid and nitric acid solutions (but not acetic acid)
Sodium chloride for standardisation of silver nitrate solutions
Sulfanilic acid for standardisation of sodium nitrite solutions
Zinc powder, after being dissolved in sulfuric or hydrochloric acid, for standardisation of EDTA solutions

29. “standard titrimetric substance” (primary standard)
More often in an ampoule contains 0,1 mol (0,1 equivalents) of substances, it is necessary for preparation of 0,1 mol/L solution.

30. Preparation rules primary solutions and definition of their titre.
The initial substance which is used for preparation of a standard solution, should be chemically pure.
The initial substance should easily and quickly react with standartized solution.
The solution of initial substance don’t change itself concentration long time.
It is necessary to use reactions between initial and defined substance, which are possible in direct titration.

31. Titration process should end quickly and accurately
Titration process should end quickly and accurately. The end point of titration should will be defined easily and precisely.
To establish of titre it is desirable either a method of accurately weighed sample or dissolution of precisely weighed initial substance in certain volume.
For the prevention of errors by titration it is necessary to choose volume of the primary standard aliquot or weighed of standard substance, that the volume of the secondary standard which will react in titration was not less than 20 mL (buret on 25 mL) or 40 mL (buret on 50 mL).

32. Titration should be carry out until then it will not be received yet three reproduced results.
Prepared of standartized solution should be stored in conditions which exclude absorption of air moisture by them, and also evaporation. A titre should not change at standing in time.
Wares and measuring devices which are used in titrimetry, should be washed up, calibrated, prepared for titration and should be stored in a pure place.
Accuracy measurement of volumes and the calculations, should correspond to accuracy of weighing.

33. Titrimetric methods are classified into four groups based on the type of reaction involved.
acid–base titrations, in which an acidic or basic titrant reacts with an analyte that is a base or an acid;
complexometric titrations involving a metal–ligand complexation reaction;
redox titrations, where the titrant is an oxidizing or reducing agent;
precipitation titrations, in which the analyte and titrant react to form a precipitate.

34. Requirements to reactions in titrimetric analysis
all reactions involving the titrant and analyte must be of known stoichiometry, quantitatively
the titration reaction must occur rapidly
a suitable method must be available for determining the end point with an acceptable level of accuracy
Reactions should proceed by room temperature
Titration should not be accompanied by collateral reactions which deform the results of the analysis
Reactions should be specific

35. 2. Techniques of titrimetric analysis.
Washing up and drying ware
Preparation of standard solutions
Sample preparation
Titration:
- Measurement of volumes
- An indicator choice
Calculations

36. Common examples of glassware used to measure volume:
The Buret (or burette)
beaker
transfer pipet;
volumetric flask
Graduated cylinders
measuring pipet

37. Calibration: volumetric flask - an injection method
pipettes, burettes - a pouring out method

38. Methods to determine the end point
visual indicators:
Colour change: In some reactions, the solution changes colour without any added indicator. This is often seen in redox titrations, for instance, when the different oxidation states of the product and reactant produce different colours.
Precipitation: If the reaction forms a solid, then a precipitate will form during the titration. A classic example is the reaction between Ag+ and Cl- to form the very insoluble salt AgCl. This usually makes it difficult to determine the endpoint precisely. As a result, precipitation titrations often have to be done as "back" titrations (see below).
Physical and chemical methods with the subsequent analysis of curves of the titration showing changes which occur in the course of titration (change of physical and chemical parametres standard solutions)

39. 3. Types of titrimetric determinations.
Titration can be:
direct titration
back-titration (on residue)
substitute-titration (displacement titration)
revertive titration

40. Requirements to reactions in direct titration
direct titration – titrant add to an analyte solution and react with determined substrance
Requirements to reactions in direct titration
reaction involving the titrant and analyte must be of known stoichiometry, quantitatively
the titration reaction must occur rapidly
a suitable method must be available for determining the end point with an acceptable level of accuracy
Reactions should proceed by room temperature
Titration should not be accompanied by collateral reactions which deform the results of the analysis
Reactions should be specific
a suitable indicator is available
А + Т = product

41. This titration is used, when: Тresidue + Тpadding = product2
Back titration. A titration in which a reagent is added to a solution containing the analyte, and the excess reagent remaining after its reaction with the analyte is determined by a titration.
This titration is used, when:
the titration reaction is too slow,
a suitable indicator is not available,
there is no useful direct titration reaction
the standard solution lacks of stability (fugitive)
А + Тexcess = product1 + Тresidue
Тresidue + Тpadding = product2

42. This titration is used, when:
displacement titration. A titration in which the analyte displaces a species, usually from a complex, and the amount of the displaced species is determined by a titration.
This titration is used, when:
the analytes are unstable substance
It is impossible to indicate the equivalent (end) point in direct reaction
Analyte doesn’t react with titrant
reaction involving the titrant and analyte mustn’t be of known stoichiometry, quantitatively

43. А + Т1(padding compounds) = А1(substituent)
А1(substituent) + Т = product
CrCl2 + FeCl3 = CrCl3 + FeCl2
analyte substitute
5FeCl2 + KMnO4 + HCl = 5FeCl3 + KCl + MnCl2 + 4H2O

44. А(in burette) + Т(in flask) = product
Revertive titration.
A standard solution is titrated by solution of investigated substance in reversive titration
А(in burette) + Т(in flask) = product

45. 4. Calculations in titrimetric analysis.
Weight of investigated substance by results of direct, displacement or reversive titration:

46. Weight of investigated substance by results of back titration:

47. Titre of titrant by investigated substance:

48. The basic reaction of a method:
5. PROTOLYTOMETRY OR ACID–BASE TITRATION (A NEUTRALIZATION METHOD): THE BASIC CONCEPTS, TITRANTS, DEFINED SUBSTANCES.
Acid–base titration - titration in which the reaction between the analyte and titrant is an acid–base reaction.
Protolytometry is titrimetric method of analysis which uses solutions of acids or bases as titrants. In this method of the analysis defined substances are the substances, capable to react with acids and the bases.
The basic reaction of a method:
Н+ + ОН- = Н2О or
HA + B = BH+ + A-

49. Methods of acid-base titration or acid–base titrimetry:
acidimetry (titrants - HCl, H2SO4)
alkalimetry (titrants - NaOH, KOH)
All titrants are secondary standard solutions, therefore demand of standardization (definition of precise concentration).

50. Standardization of acidic titrants - solutions of acid HCl, H2SO4
Standard (reference) substances – sodium tetraboratic Na2B4O75H2O or Na2B4O710H2O, sodium carbonate Na2CO3:
Na2B4O7 + 2HCl + 5H2O = 2NaCl + 4H3BO3
Na2CO3 + 2HCl = 2NaCl + CO2 + H2O

51. Standardization of НСl solution on sodium tetraborate.
Weigh exact shot of Na2B4O75H2O or Na2B4O710H2O and place it in a measured flask, dissolve in hot water, after a solution is cooled and diluted of solution by water to necessary volume and it is mixed.
In a flask for titration place an aliquot of prepared primary standard solution Na2B4O75H2O or Na2B4O710H2O, add some drops of the methyl orange. The received solution is titrated by solution of НСl to change of colour with yellow to orange with a rose shade.

52. Standardization of НСl solution on sodium tetraborate
Standardization of НСl solution on sodium tetraborate. By 3-4 results of titration calculate average volume of used titrant and calculate concentration of hydrochloric acid.

53. Standardization of HCl solution on sodium carbonate
In a flask for titration place exact shot of sodium carbonate, dissolve in necessary volume of water, add some drops methyl orange and titrate this solution by chloric acid.
Such titration repeat for 3-4 times. Each time calculate concentration of HCl:
By 3-4 results of titration calculate average concenration of chloric acid.

54. Standardization of basic titrants - solutions of bases of NaOH, KOH
Standard (reference) substances – oxalate acid H2C2O42H2O, succinate acid H2C4H4O4:
H2C2O4 + 2NaOH = Na2C2O4 + 2H2O
H2C4H4O4 + 2NaOH = Na2C4H4O4 + 2H2O

55. Standardization of NaOH solution on oxalic acid.
Weigh exact shot of H2C2O42H2O and place it in a measured flask, dissolve in hot water, after a solution is cooled and diluted of solution by water to necessary volume and it is mixed.
In a flask for titration place an aliquot of prepared primary standard solution H2C2O42H2O , add some drops of the phenolphthalein. The received solution is titrated by solution of NaOH to change of colourless to rose (or red).

56. Standardization of NaOH solution on oxalic acid
Standardization of NaOH solution on oxalic acid. By 3-4 results of titration calculate average volume of used titrant and calculate concentration of NaOH.

57. CH3COOH + NH4OH = CH3COONH4 + H2O
According to force of acid and the base such types of the acid-base interaction are possible:
Between strong acid and the strong basis
NaOH + HCl = H2O + NaCl
Between weak acid and the strong basis
NaOH + CH3COOH ↔ CH3COONa + H2O
Between strong acid and the weak basis
NH4OH + HCl = NH4Cl + H2O
Between weak acid and the weak basis
CH3COOH + NH4OH = CH3COONH4 + H2O

58. Indicators of acid-base titration
6. INDICATOR CHOICE, CALCULATION OF ERRORS OF TITRATION IN A METHOD PROTOLYTOMETRY.
Indicators of acid-base titration
The substances which colouring changes depending on size change рН of solution.
Requirements to indicators:
Indicator colouring at near values рН should differ well
Change of colouring of the indicator should occur sharply in a small interval of рН
Indicator colouring should be as it is possible more intensively
The quantity of base or acid, necessary for change of colouring of the indicator, should be very small
Change of colouring of the indicator must to be reversible

59. 1894 – the ionic theory of indicators
Indicators of an acid-base titration method are weak acids or the bases at which not ionised molecules and ions have different colouring
HInd ↔ H Ind-
Lacmus red blue
Phenol-
phthalein colourless rose
Ind: - one-colour (phenolphthalein )
- two-colour (methyl orange , lacmus)

60. Limitation of ionic theory of indicators :
Ascertaining of different colouring of acidic and basic forms, but is not present an explanation of presence and colouring change.
The structure and colouring are not connected.
Colouring change is ionic process but why it often is long in time?
Advantages of the ionic theory: possibility of quantitative interpretation of results of change of colouring.

61. The theory of chromophore – colouring of organic compounds is connected with presence of a chromophore groups at molecules of indicators :
Auxochrome groups haven’t colouring, but with a chromophore groups strengthen action of the last, causing deeper intensity of colouring.

62. Colouring change is a consequence of isomeric transformation which changes an indicator structure
The colourless form The yellow form

63. Limitation of chromophore theory of indicators
Does not give an explanation why tautomeric transformations and change of colouring of a solution of indicators occurs at change рН a solution.
Colouring changes instant, where as intra-molecular transformations generally long processes is frequent.
Does not give a quantitative estimation of connection of colouring change with change рН.

64. The ionic- chromophore theory
The acid-base indicators are weak acids and the bases, and the neutral molecule of the indicator and its ionised form contain different chromophore groups
colourless yellow yellow

65. The ionic- chromophore theory
НInd0 ↔ HInd ↔ H+ + Ind-
the acid the base
form form

66. рТ of most often used indicators in the acid-base titration:
Methyl orange ,0
Methyl red ,5
Lacmus ,0
Phenolphthalein ,0
pT of the indicator is value of рН at which colour of the indicator sharply changes and stop to add titrant (there is end point of titration)

69. Factors which influence the indicator indication.
At increase tо the temperature indicator becomes less sensitive to Н+ -ions for indicators-bases
Presence of organic solvent (alcohol, acetone), albuminous molecules, salts changes рК of the indicator
It is necessary to define titre a working solution in the same conditions at which the test analysis is conducted
it isn’t recommended to take a lot quantity of indicator

70. Indicator choice spend two methods:
2. Indicator choice, calculation of errors of titration in a method protolytometry.
Indicator choice spend two methods:
On reaction products
On titration curves

71. Titration curve for 0,1 mol/L hydrochloric acid by 0,1 mol/L sodium hydroxide

72. Dependence of inflection points on concentration of defined substance (0,1 mol/L and 0,01 mol/L)

73. Dependence of inflection points on force of acid

74. Dependence of inflection points on force of acid

75. Titration curve for weak acid (CH3COOH) by weak base (NH4OH)

76. Titration curve for H3PO4 by NaOH

77. Factors which influence on inflection points
constants of acid or base
temperatura of solutions
concentration of defined substances
concentration of used titrants

78. Choice of the indicator: The pT of indicator (interval of transition of colouring - pH range) should be in limit of inflection points on a titration curve

79. Choice of the indicator: The pT of indicator (interval of transition of colouring - pH range) should be in limit of inflection points on a titration curve

80. Titration curve of 0.100 M HCl with 0.200 M NaOH

81. Titration curve of 0,1 М CH3COOH by 0,2 M NaOH

82. Titration curve of 0,1 М NH3 by 0,1 M HCl

83. Titration curve of weak acid by weak base

84. Titration curve for 50. 00 mL of 0. 100 M CH3COOH with 0
Titration curve for mL of M CH3COOH with M NaOH showing the range of pHs (or pT) and volumes of titrant over which the indicators bromothymol blue and phenolphthalein are expected to change color.

85. Titration curve of mix 0,1 M HCl + 0,1 M CH3COOH by 0,1 М NaOH
Acetic acid
Ка=1,74·10-5

86. Titration curve of mix acetic and malatic acids
Acetic acid Ка=1,74·10-5
К1:К2<104

87. Titration curve of maleinic acid

88. Titration curve 0,1 М oxalic acid by 0,1 М NaOH

89. Determinate the end-point by potentiometric way

90. Titration error - the determinate error in a titration due to the difference between the end point and the equivalence point. Indicator’s error
“+” – if have excess of base when define acid
“-” – if have rest of acid when define acid
Hydroxonium error

91. Indicator’s error :
Hydroxyl error
Acidic error
Bases error

92. 7. NONAQUEOUS ACID–BASE TITRATION.
Titration in water solutions is limited by factors:
It is impossible to titrate for a mix of acids or the bases if constants of dissociation differ less, than on four order
It is impossible to titrate for a mix of strong and weak acids (bases)
It is impossible to titrate very weak acids (bases)
It is impossible to titrate separately for a mix of acids (bases) with near constants of dissociation
It is impossible to define substances which are insoluble in water.

93. Choice of solvents:
The constant of autoprotolysis solvent should be as small as possible
For titration of the weak bases should be to take a solvent with the expressed progenic properties (the acid nature of solvent)
For titration of weak acids should be to take a solvent with expressed protophilic properties, (the basis nature of solvent)
Dielectric inductivity of solvent should be as it is possible above

94. The weak bases often are titrated in the acetic acid medium (strengthening of force of the bases)
Titrant: perchlorate acid HClO4
Standardization: on potassium hydrogenphthalate, or on sodium salicylate if have solution of HClO4 in CH3OH

95. Nonaqueous acid–base titration of weak bases by perchlorate acid
Indicators: crystal violet (violet – blue or
green),
thymol dark blue (yellow – rose).

96. The weak acids often are titrated in the medium dimethyl formamide, ethylene diamine, butylamine, pyridine (strengthening of force of the acids)
Titrant: sodium hydroxide NaOH in the solution of benzene with methanol
sodium methylate CH3ONa in methanol or in the solution of benzene with methanol.

97. Standardization of NaOH and CH3ONa on benzoic acid

98. Nonaqueous acid–base titration of weak acids by NaOH or CH3ONa
Indicators: thymol blue (red-yellow and yellow-blue) or physico-chemical methods (potentiometry).

99. In nonaqueous acid–base titration determinate the end-point by potenthiometric way

100. In nonaqueous acid–base titration determinate the end-point by potenthiometric way

101. Thanks for your attention!