ABSTRACT

INTRODUCTION

* Titration is the addition of a known concentration of base / acid to a solution of acid/base of unknown concentration. Since both volumes of the acid and base are known the concentration of the unknown solution is then mathematically determined. [1]

* the word “titration” is the process of finding out how much of a certain substance is contained in a solution by measuring how much of another substance it is necessary to add to the solution in order to produce a given reaction.[2]

IMPORTANT TERMS:

TITRANT: a reagent with known concentration, whose volume is added to the analyte solution. It is also called as “titrator”. [1]

ANALYTE: a substance whose concentration will be determined by the process of titration. [1]

EQUIVALENCE POINT: It is the point in a titration when the amount of added standard reagent is exactly equivalent to the amount of analyte. [1]

BACK TITRATION: It is a process in which the excess of a standard solution used to consume an analyte is determined by titration with a second standard solution. [1]

END POINT: It is the point in a titration at which an observable physical change signals the equivalence point.

INDICATOR: An indicator is (often) a weak acid that is placed into the unknown solution to determine the endpoint of the titration (the pH at which the indicator changes color). It is often added to the analyte solution to produce an observable physical change (the end point) at or near the equivalence point.

PRIMARY STANDARD: It is an ultrapure compound that serves as the reference material for a titrimetric method of analysis. Or in other words, it is a highly purified compound that serves as a reference material in volumetric and mass titrimetric methods

SECONDARY STANDARD: It is a compound whose purity has been established by chemical analysis and that serves as the reference material for a titrimetric method of analysis. [1]

CLASSIFICATION

The method of titration can be classified on following basis;[3]

ON THE BASIS OF TYPE OF REACTION:

1) [4]Acid-Base Titrations: is a process of neutralization whereby a titrant is delivered into an analyte until the unknown solution is completely neutralized. This will allow information about the unknown solution to be determined by the help of an indicator.

2) Red-ox titration: titration of a reducing agent by an oxidizing agent or titration of an oxidizing agent by a reducing agent. The concentrations of redox-active species can be determined by redox titrations. In a redox titration, a measured sample of the unknown is titrated against a standard solution of a substance that will oxidize or reduce the unknown.

On the basis of type of reaction

1. Acid- base titration 2. Redox titration3. Complexometric

titration4. Zeta potential titration5. Iodimetric titration6. Precipitation titration7. Kjeldahl titration8. Argenometric titration

a) The Mohr titrationb) Volhard titrationc) Fajans titration

On the basis of end-point techniques

1. Potentiometric titration

2. Spectrophotometric titration

3. Amperometric titration

4. Thermometric titration

5. Nonaqueous titration

6. Automatic titrationFurthermore it also includes;

1. Back titration2. Virus

titration

3) Complexometric Titrations (i.e.,Complex formation ,chelometric): technique involves titrating metal ions with a complexing agent or chelating agent (Ligand) and is commonly referred to as complexometric titration. A technique of volumetric analysis in which the formation of a colored complex is used to indicate the end point of a titration. Also known as chelatometry. These titrations are based on the formation of a complex between the analyte and the titrant.[4]

4) Zeta potential titration : is a titration of heterogeneous systems, such as colloids, emulsions, etc. Solids in such systems have very high surface area. This type of titration is used to study the zeta potential of these surfaces under different conditions. The Iso-electric point is one such property. The iso-electric point is the pH value at which the zeta potential is approximately zero. At a pH near the iso-electric point, colloids are usually unstable; the particles tend to coagulate or flocculate. Such titrations use acids or bases as titration reagents[5].

5) Miscellaneous titration: a form of titration can also be used to determine the concentration of a virus or bacterium. The original sample is diluted (in some fixed ratio, such as 1:1, 1:2, 1:4, 1:8, etc.) until the last dilution does not give a positive test for the presence of the virus. This value, the titre, may be based on TCID50, EID50, ELD50,LD50 or pfu. This procedure is more commonly known as an assay.[6]

6) Iodimetry titration: iodimetry is a method of volumetric chemical analysis, a titration where the appearance or disappearance of elementary iodine indicates the end point. Usual reagents are sodium thiosulfate as titrant, starch as an indicator (it forms blue complex with iodine molecules - though polyvinyl alcohol has started to be used recently as well), and an iodine compound (iodide or iodate, depending on the desired reaction with the sample)[5].

7) Precipitation titration: also called as Amperometric titration in which the potential of a suitable indicator electrode is measured during the titration. In a precipitation titration, one of the products is a precipitate.

8) Kjeldahl Titration: was developed over 100 years ago for determining the nitrogen contents in organic and inorganic substances. Although the technique and apparatus have been modified over the years, the basic principles introduced by Johan Kjeldahl still endure today.Kjeldahl nitrogen determinations are performed on a variety of substances such as meat, feed, grain, waste water, soil, and many other samples.[6]

9) Argentometric Titrations: titrimetric methods based on silver nitrate are sometimes called argentometric methods.[4]

The Mohr titration:In this method Sodium chromate can serve as an indicator for the argentometric determination of chloride, bromide , and cyanide ions by reacting with silver ion to from a brick-red silver chromate precipitate in the equivalence –point region.

The Fajan titration:In this method a coloured indicator is absorbed onto the precipitate at end point .Absorption indicator is an organic compound that tends to be adsorbed onto the surface of the solid in a precipitation titration. The adsorption occurs near the equivalence point and results not only in a color change but also in a transfer of

color from the solution to the solid. Fluorescein is a typical adsorption indicator that is useful for the titration of chloride ion with silver nitrate.

Volhard titration:Determination of the halogen content of a solution by titration with a standard thiocyanate solution.[4]

CLASSIFICATION BY END-POINT TECHNIQUES:

[7]The precision and accuracy with which the end point can be detected is a vital factor in all titrations. Because of its simplicity and versatility, chemical indication is quite common, especially in acid-base titrimetry.

01) Potentiometric titration: titration in which the end point is determined by measuring the voltage of an electric current of given amperage passed through the solution. If a pH meter is used, its associated electrodes are first standardized by use of a buffer solution of known pH. By suitable choice of electrodes, potentiometric methods can also be applied to combination titrations and to oxidation-reduction titrations.

03) Spectrophotometric titration in this method, We can use absorption of light to monitor the progress of the reaction.The spectrophotometer is an optical device that responds only to radiation within a selected very narrow band of wavelengths in the visual, ultraviolet, or infrared regions of the spectrum. The response can be made both quantitative and linearly related to the concentration of a species that absorbs radiation within this band. Titrations at wavelengths within the visual region are by far the most common.

04)Amperometric titration; by use of a dropping-mercury or other suitable microelectrode, it is possible to find a region of applied electromotive force (emf) in which the current is proportional to the concentration of one or both of the reactants in a titration.Biamperometric titration is a closely related technique. An emf that is usually small is applied across two identical micro-electrodes that dip into the titrant solution. [7]

05) Thermometric or enthalpimetric titration: in this; chemical reactions proceed with the evolution of heat. The temperature first rises progressively and then remains unchanged as the titration is continued past the end point. If the reaction is endothermic, the temperature falls instead of rising. Thermometric titration is applicable to all classes of reactions.

06) Nonaqueous titration: is the titration of substances dissolved in nonaqueous solvents. It is the most common titrimetric procedure used in pharmacopoeial assays and serves a double purpose .This technique is used to perform titrations that give poor or no end points in water. Although applicable in principle to all classes of reactions, acid-base applications have greatly exceeded all others. Nonaqueous titrations in which the solvent is a molten salt or salt mixture are also possible.

07)Automatic titration: the whole process of titration is made much easier by making it automated. You simply add a predetermined amount of reactant and the

machine will add the other reactant and measure the products to find the end point. Automation is particularly valuable in routine titrations, which are usually performed repeatedly. One approach is to record the titration curve and to interpret it later. Another method is to stop titrant addition or generation automatically at, or very near to, the end point. Although a constant-delivery device is desirable, an ordinary buret with an electromagnetically controlled valve is often used.Microcomputer control permits such refinements as the continuous adjustment of the titrant flow rate during the titration. In some cases, it is possible to automate an entire analysis, from the measurement of the sample to the final washout of the titration vessel and the printout of the result of the analysis.

08) Electrochemical titration; in this way we detect a voltage change between electrodes.[8]

OTHERS:

[9]Back titrations: these are like normal titrations, except that a known excess of a standard reagent is added to the solution being titrated. The solution is then titrated back, taking into account the addition of the excess. Back titrations are useful if the end point of the reverse titration is easier to identify than the end point of the normal titration.

Virus titration: these are used to determine the virus concentration. It may be based on TCID50 EID50,ELD50, LD50 or pfu.[9]

INTRODUCTION TO TIRATION BASED ON NEUTRALIZATION

DEFINITION

[1]A neutralization reaction is such type of reaction when an acid   and a base react to form water and a salt which involves the combination of H+ ions and OH- ions to generate water.

Acid + Base → salt + water [10]

EXPLANATION

[11] The word "neutralization" also called water forming reaction, is used because the acid and base properties of H+ and OH- are destroyed or neutralized. In the reaction, H+ and OH- combine to form H2O or water molecules. Neutralization is a type of double replacement reaction. A salt is the product of an acid-base neutralization reaction.EXAMPLE: -

HCl + NaOH NaCl + HOH

H2SO4 + 2 NH4OH (NH4)2SO4 + 2 HOH

2 NaOH + H2CO3 N2CO3 + 2 NaOH [2]

TYPES OF NEUTRALIZATION REACTIONS

1. Strong Acid-Strong Base Neutralization[12]When a strong acid and a strong base react, the products are always water and a salt. The formula of the salt depends on the anion of the acid and the cation of the base. The overall pH of the solution will be neutral which means that the pH is equal to 7.00, because the salt does not affect the pH and water is neutral. [12]

Example:-

HCl(aq)+NaOH(aq )⇋  NaCl(aq)+H2O(l)

Strong acid + Strong base⇋ Neutral salt + water

2. Weak Acid-Weak Base Neutralization:-

[12][13]Both the weak acid HA and the weak base B are largely undissociated, and the neutralization reaction between them therefore involves proton transfer from the weak acid to the weak base.When a weak acid and a weak base react, the products are only a salt.

The pH of the solution formed from the reaction of a weak acid with a weak base depends on the relative strengths of the reactants. For example, if the acid HClO has a Ka of 3.4 x 10-8 and the base NH3 has a Kb = 1.6 x 10-5, then the aqueous solution of HClO and NH3 will be basic because the Ka of HClO is less than the Ka of NH3.

HClO + NH3  NH4ClO

Example:-

The net ionic equation for the neutralization of Acetic acid with aqueous ammonia is:

CH3CO2H (aq) + NH3 (aq) ⇋ NH4+ (aq) + CH3CO2

-(aq)

3. Weak Acid Strong Base Neutralization:-

As the weak acid HA is largely undissociated, the net ionic equation for the neutralization reaction of a weak acid with a strong base involves proton transfer from HA to the strong base OH-.When a weak acid and a strong base react, the products are also water and a salt.

Example:-

Acetic acid (CH3CO2H) reacts with aqueous NaOH to give water and aqueous sodium acetate (CH3CO2Na):

CH3CO2H (aq) +OH-(aq) ⇋ H2O (l) + CH3CO2

-(aq)

(Na+ ions do not appear in the net ionic equation because both NaOH and CH3CO2Na are completely dissociated.)

4. Strong Acid Weak Base Neutralization:-

The strong acid HA is completely dissociated into H3O+ and A- ions, and its neutralization reaction with a weak base therefore involves proton transfer from H3O+ to the weak base B:

H3O+ (aq) + B (aq) ⇋ H2O (l) + BH+

(aq)

When a strong acid and a weak base react, the products are also water and a salt.

Example:-

The net ionic equation for neutralization of hydrochloric acid with aqueous ammonia is:

H3O+ (aq) + NH3 (aq) ⇋ H2O(l) + NH4+

(aq) [12][13]

GENERAL PROCEDURE

1) [14] A known volume of the analyte (acid) is placed in a titration flask.2) The burette is filled by a standard solution (titrant, base) of known

concentration.3) Before the titration is started, 1-3 drops of indicator (eg, phenolphthalein) is

added in the titration flask with the analyte (acid). The chosen indicator must be one color when the solution is acidic.

4) A base solution is then slowly added from the burette, drop by drop.5) The titration continues, drop by drop, until the indicator suddenly achieves

the intermediate color (weak pink) between that of the acid and the color of the base (fuchsia). At that point the titration ceases.

6) The point at which the system is neither acidic nor basic is referred to as the “endpoint” or the “neutralization point”. The endpoint will correspond to a perfect stoichiometric relationship between the acid and the base.

7) Once the endpoint has been reached, the burette must be read. The bottom of the meniscus line determines the quantity of the base VT that was required to reach the endpoint. [14]

COMPARISION BETWEEN AQUEOUS AND NON-AQUEOUS

NEUTRALIZATION TITRATION

[15]The apparent strength of an acid or base is determined by the extent of its reaction with a solvent. In aqueous solution all strong acids appear equally strong because they react with the solvent to undergo almost complete conversion to hydronium ion (H3O+) and the acid anion. In a weakly protophilic solvent such as acetic acid, the extent of formation of the acetonium ion (CH3COOH2

+) due to the addition of a proton provides a more sensitive differentiation of the strength of acids and shows that the order of decreasing strength for acids is perchloric, hydrobromic, sulfuric, hydrochloric, and nitric acid.

This so-called levelling effect is observed also for bases. In sulfuric acid almost all bases appear to be of the same strength. As the acid properties of the solvent decrease in the series sulfuric acid, acetic acid, phenol, water, pyridine and butylamine, bases dissolved in them become progressively weaker and the differences between bases are accentuated. In order of decreasing strength, strong bases of value for non-aqueous titrations are potassium methoxide, sodium methoxide and lithium methoxide.

Many water-insoluble compounds acquire enhanced acidic or basic properties when dissolved in organic solvents. Thus the choice of the appropriate solvent permits the determination of a variety of such materials by non-aqueous titration. Pure compounds can be titrated directly, but it is often necessary to isolate the active ingredient in pharmaceutical preparations from interfering excipients and carriers.

The types of compounds that may be titrated as acids include acid halides, acid anhydrides, carboxylic acids, amino acids, phenols, enols such as barbiturates.

The types of compounds that may be titrated as bases include amines, quarternary ammonium compounds, and alkali salts of organic acids. [15]

COMMON EXAMPLES OF NEUTRALIZATION REACTIONS

[16]When soil turns acidic and slaked lime or lime stone is added to the soil, neutralization takes place. 

When an ant stings on the skin and baking soda is applied on the skin for relief, neutralization takes place. Ant sting is acidic (due to formic acid) and baking soda is basic (due to sodium bicarbonate). Wasp sting on the other hand is basic and vinegar (contains acetic acid) is used for relief on wasp sting. 

When acidic wastes from factories are disposed off in rivers, they are first treated with bases so as to neutralize the wastes first and prevent the river water from getting acidic.

Another one is when you drink orange juice or anything acidic, when you brush your teeth with toothpaste, which contains bases, they are neutralized to protect teeth. [16]

APPLICATIONS OF NEUTRALIZATION

When acidic and basic solutions containing hydroxide are mixed, a neutralization reaction occurs in which acid & base loss their characteristic properties. These reactions are important in both nature and industry, because Ph has profound effect on chemical processes therefore neutralization is important for maintenance of pH.1-First-Aid Treatments Use Neutralization[17]A toilet bowl cleaner is danger corrosive which produces chemical burns. It contains Hydrochloric Acid which should not get in eyes, on skin. It may be fatal if swallowed. First-Aid to avoid the harms against Bowl cleaner is a teaspoon of magnesia, chalk, small pieces of soap, raw egg white, or milk which dilutes the acid coating the stomach lining or neutralizing it. [17]

Example: Mg (OH)2 + HCl --> MgCl2 + HOH2-Use of Neutralization in agricultural[18]Neutralization has many practical applications. For example, agricultural land is often too acidic or too basic to grow certain crops. Farmers can add either a weak acid or a weak base to produce the level of acidity or basicity in which various plants grow best. Reclamation (restoration) of land once used for mining also involves neutralization reactions. Such land is often too acidic for plants to grow.

Treating the land with calcium oxide neutralizes acids remaining in the soil and restores its fertility. [18]

3- Use of neutralization in environmental problems[19]Neutralization is also used to deal with environmental problems. Gases produced in factories, power generating plants, and other industrial facilities are usually acidic. When they escape into the air, they react with water to form acid rain. Scrubbers that contain bases can be attached to the inside of smokestacks in such plants to neutralize acids in escaping gases. Treatment with acids or bases is also used to neutralize hazardous chemicals produced by a variety of manufacturing operations. [19]

4- Use of neutralization in medicine[16]When someone suffers from acidity, some antacids are given to eat so that neutralization can take place in the stomach of the patient. Stomach has hydrochloric acid in it whereas a popular antacid is milk of magnesia which contains Mg (OH)2 . [16]

REDOX TITRATION:

Redox Titration is known as the oxidation-reduction reaction. It is basically a transfer of one electron from one reactant to another. When oxidation happens, reduction will also happen.

these titrations involve the titration of an oxidizing agent (or oxidant) with a reducing agent (or reductant) or vice versa. There must be a sufficiently large difference between the oxidizing and reducing capabilities of these agents for the reaction to undergo completion with a sharp end point.[20]

EXAMPLE:

An example of a redox titration is treating a solution of iodine with a reducing agent and using starch as indicator. Iodine forms an intensely blue complex with starch. Iodine (I2) can be reduced to iodide (I−) by, for example, thiosulphate (S2O3

2−), and when all iodine is spent the blue color disappears. This is called an iodometric titration. Most often, the reduction of iodine to iodide is the last step in a series of reactions in which the initial reactions are used to convert an unknown amount of the solute (the substance you want to analyze) to an equivalent amount of iodine, which can then be titrated.[20]

SIMILARITY BETWEEN REDOX AND ACID BASE REACTION:

Redox reactions, or oxidation-reduction reactions, have a number of similarities to acid–base reactions. Like acid–base reactions, redox reactions are a matched set, that is, there cannot be an oxidation reaction without a reduction reaction happening simultaneously. The oxidation alone and the reduction alone are each called a half-reaction, because two half-reactions always occur together to form a whole reaction. When writing half-reactions, the gained or lost electrons are

typically included explicitly in order that the half-reaction be balanced with respect to electric charge..[21]

OXIDIZING AGENT:

Oxidation process involves loss of electrons while reduction process involves gain of electrons. Thus an oxidizing agent is one which accepts electrons while a reducing agent is one which loses the electrons. An oxidizing agent oxidizes the other substance by stripping off electrons from it.

EXAMPLE:i.  KMnO4 in presence of dil H2SO4

MnO4¯    +  8H+  +   5e-     →     Mn2+      +    4H2O            E°red = +1.52V

 ii. K2Cr2O7 in dil. H2SO4

a moderately strong oxidizing agent; oxidizing ability depends strongly on pH, decreasing rapidly as solution becomes more neutral

Cr2O72– + 14H+ + 6e– → 2Cr3+ + 7H2O                          E°red = +1.33V

iii.  Iodine solution                                                                   I2  + 2 e-  =  2I–                                                       E°red = +0.54V

REDUCING AGENT:

A reducing agent reduces the other substance by donating electrons to it.Oxidation and reduction reactions always occur simultaneously. One cannot take place in isolation from the other. During a redox reaction the oxidizing agent itself undergoes reduction while the reducing agent undergoes its oxidation[20]

EXAMPLES i.   Mohr’s salt    FeSO4.(NH4) 2SO4.6H2O                                 Fe2+       →    Fe3+       + e-                                       E°red = +0.77V ii. Oxalic acid      H2C2O4.2H2O                                          

C2O42-  = 2CO2  + 2 e-                                  E°red = +0.77V

 iii Sodium thiosulphate  Na2S2O3.5H2O                                                     

2S2O32-  = S4O6

2- + 2 e-                                 E°red =  +0.08V 

 There is no universal oxidizing agent which can be titrated against every reducing agent and vice-versa. Hence, the choice of an oxidizing agent to be used against a particular reducing agent depends upon the reaction conditions and standard reduction potential of the oxidizing agent.[20]

 

REDOX EQUATION AND HALF REACTION EQUATION:

Before one can balance an overall redox equation, one has to be able to balance two half-equations, one for oxidation (electron loss) and one for reduction (electron

gain). After balancing the two half-equations one can determine the total net reaction.

Each equation is balanced by adjusting coefficients and adding H2O, H+, and e- in this order:

1. Balance the number of atoms of each element. 2. Balance the number of electrons transferred.3. Balance the total charge on reactants and products

Balancing Oxidation-Reduction Reactions

To solve redox reactions accurately, you must first understand how to balance chemical equations. Though this process is more difficult than normal balancing it is a required step in the process of redox reactions. One of the most accepted methods of balancing a redox reaction is known as the half-equation method, however it can become more complex when involving basic or acidic solutions.

Half-Equation Method

The half-equation method (for neutral reactions) involves three basic steps which are as follows:

Write and balance the half reactions. Adjust coefficients in both equations so that the same number of electrons appears

in each half. Add together both halves, canceling out electrons, to obtain the overall equation.

[22]

REDOX INDICATORS

            A redox indicator should be such that it produces a sudden change in the electrode potential in the vicinity of the equivalence point during a redox titration. This is possible when the indicator itself is redox active i.e., capable of undergoing oxidation or reduction process which is a reversible one. The oxidized and reduced form of the indicator should have a contrast difference in the colours.

Color Change for a Redox Indicator occurs mostly over the range:

OR

E=(Eo±0.05916n )volts

At potential E, the ratio of the concentration of two forms is given by the Nernst equation

ET = E0  +  RT/nF ln [Inoxd]/[IRed]

In order to be useful in endpoint detection, a redox indicator’s range of color change should match the potential range expected at the end of the titration.[23]

TYPE OF REDOX INDICATORS Self Indicators  Many a times the titrant itself may be so strongly coloured that after the equivalence point, a single drop of the titrant produces an intense colour in the reaction mixture. e.g. potassium permanganate. Such Indicators are called self indicators. Self indicators generally are strongly coloured as a result of charge transfer transitions in them. Internal indicator  Such indicators are added into the reaction mixtures Such indicators always have reduction potential values lower than the analyte system so that they react with the titrant only when whole of the analyte has been consumed, producing a readily detectable color change. External indicator  In case a suitable redox indicator is not available for a given system, an indicator may be employed which will indicate the completion of reaction by physically or chemically reacting with the analyte (not through redox reaction). This reaction between indicator and the analyte may sometimes be an irreversible one and in some cases may even lead to precipitation.  In those case indicators are not added to the reaction mixture on the whole, rather used externally on a grooved tile. Such indicators are called external indicators.  Potentiometric Methods The most accurate method to judge the completion of redox titration is however potentiometric method  which deals with the measurement of e.m.f.  between a reference electrode and the indicator (redox) electrode during the stages of redox titration. This method infact tells us the equivalence point of the reaction and not the end point.[23]

NON AQUEOUS TITRATION

INTRODUCTION:

The Lowry-bronsted theory of acid and bases can be applied equally well to reactions occurring during acid base titrations in non-aqueous solvents. This is because this approach considers an acid as any substance, which will tend to donate a proton, and a base as any substance, which will accept a proton. Substances which give poor end points due to being weak acids or bases in aqueous solution will frequently give far more satisfactory end point when titrations are carried out in non-aqueous media. An additional advantage is that many substances, which are insoluble in water, are sufficiently soluble in organic solvents to permit their titrations in these non-aqueous media.[24]

Example 1: Amine salt; it is first change to the water soluble free base extracted with an appropriate organic solvent and treated with an access volume of standard

acid, subsequently the water will evaporate, and the remaining acid is determined with a standard base. Example 2: sodium salts; it is first acidified to release the water in soluble organic acid, extracted with a suitable organic solvent, the solvent is removed & the residue is subsequently dried and weighed.In order to overcome these short comings the non-aqueous titrations were introduced.[24]

TYPES OF NON AQUEOUS TITRATION:

Direct titrations:

Residual titrations:

Complexometric titrations: [26]

SOLVENTS:

There are three types of solvents that are discussed below.1) PROTOPHILLIC SOLVENTS:

They are essentially basic in nature and normally react with acids to forms solvated protons;e.g.: HB+S ↔ SH+ + B-

2) PROTOGENIC SOLVENTS: They are acidic in nature and character e.g. sulphuric acid. They exert a leveling effects on bases i.e, the become indistinguishable in strength when dissolved in strongly basic solvents due to their enhanced affinity of strong bases for protons.

3) AMPHIOPROTIC SOLVENTS: They posses both protophillic and protogenic characterstics.

e.g., acetic acid, water and alcohol the undergo dissociation to a very less extent. Acetic acid id mostly

employed as a solvent for the titration of basic substances and its dissociation can be depicted as shown below:

CH3COOH ↔ CH3COO- + H+

In the above instance acetic acid is having as an acid.[25]

INDICATORS FOR NON-AQUEOUS TITRATIONS:

The ionized and unionized or the different resonant forms of indicators are apply equally well for non-aqueous titrations but their colour changes at the end point vary from titration to titrations, as they depend on the nature of the titrant. The colour corresponding to the correct end point may be established by carrying out a potentiometric titration while simultaneously observing the colour change of the indicator. The appropriate colour corresponds to the inflexion point

S.No

NAME OF INDICATORCOLOUR CHANGE OBSERVED

ACIDICBASIC NEUTRAL

1.Crystal violet (0.5% w/v in glacial acetic acid)

Violet Blue-greenYellowish

green

2.Oracet Blue B (0.5% in glacial acetic acid)

Blue Purple Pink

3.a - naphtholbenzein (0.2% in glacial acetic acid)

Blue or blue green

Orange Dark-green

4.Quiinalidine Red (0.1% in methanol)

Magenta _Almost

colourless

METHODOLOGY:

For non aqueous titrations, the following four steps ar usually taken into consideration, namely:

1) Preparation 2) Standardization3) Choice of indicators.4) Effect of temperature on assays.[26]

ASSAY OF METHACHOLINE CHLORIDE:

Materials Required: Methacholine chloride: 0.4 g; glacial acetic acid: 50 ml; mercuric acetate solution: 10 ml; 0.1 N perchloric acid and crystal violet solution.

Procedure: Weigh accurately about 0.4 g, previously dried and stored in a vacuum desiccator, and dissolve in 50 ml of glacial acetic acid, add 10 ml of mercuric acetate solution, one drop of crystal violet solution and titrated with 0.1 N perchloric acid to a blue-green end point. Perform a blank determination and make any necessary correction.

Each ml of 0.1 N perchloric acid is equivalent to 0.01957 g of C8H18ClNO2.

Equation:

2 [CH3COOCHCH2N+ (CH3)3].2Cl⎯ + Hg (OOCCH3)2 + 2HClO4 →

CH3

2 [CH3COOCHCH2N+ (CH3)3]. 2ClO4 − + 2HOOCCH3 + HgCl2

CH3

Mercuric acetate: It is essentially added to prevent the interference of the hydrochloric acid, which is displaced through the formation of the relatively un-ionized HgCl2, thereby making a predominant shift in the equilibrium so that the titrimetric reaction is quantitative.

Blank Titration: It is usually carried out to account for the possible reaction of atmospheric moisture with the titrant perchloric acid and also to check the titrant being employed to bring about the blue-green end-point.

Calculations: The percentage of methacholine chloride in the sample may be calculated by the following expression:

% Methacholine chloride = X ml × Normality (Calculated)× 0.01957 × 100 N(Given) × Wt. of sample(in gm)

REDOX TITRATION IN AQUEOUS SOLUTIONS:

Acid-base reactions can be characterized as proton-transfer processes, the class of reactions called oxidation-reduction, or redox, reactions are considered electron transfer reactions. Oxidation-reduction reactions are very much a part of the world around us. They range from the burning of fossil fuels to the action of household bleach. Additionally, most metallic and nonmetallic elements are obtained from their ores by the process of oxidation or reduction. Many important redox reactions take place in water, but not all redox reactions occur in aqueous solution.

S steenken - chemical reviews, 1989 - acs publications

INDICATORS:

1. Diphenylamine2. N-phenylanthranilic acid,3. ferroin4. brucine

Fluoride is added when one of the first three is used, and urea if the last is used

DETERMINATION OF ETHANOL CONCENTRATION IN AQUEOUS SOLUTION BY REDOX TITRATION:

INTRODUCTION

This method uses a redox titration to find the concentration of ethanol in an aqueous solution. The ethanol is oxidised to ethanoic acid by reacting it with an excess of potassium dichromate in acid. [32] 

The amount of unreacted dichromate is then determined by adding potassium iodide solution which is oxidised by the potassium dichromate forming iodine. [32

The iodine is then titrated with a standard solution of sodium thiosulfate and the titration results are used to calculate the ethanol content of the original solution. [32

Because alcoholic beverages such as wine or beer contain other oxidisable substances that could interfere with the titration, the dichromate solution is placed in a flask and the alcoholic beverage sample is suspended in a small container above it (see diagram).The water and ethanol slowly evaporate and as the ethanol comes in contact with the dichromate it first dissolves, and is then oxidised. More ethanol evaporates until eventually all the ethanol from the beverage has left the sample and reacted with the dichromate. Since this transfer takes time, it is necessary to leave the flask with the suspended sample in a warm place overnight. [32

EQUIPMENT NEEDED[32

250 mL conical flasks with rubber stoppers burette5 mL beakers or small glass vialsbeer or wine sample10 mL and 1 mL pipettesincubator (optional)

SOLUTIONS NEEDED[32

Acid dichromate solution: (0.01 molL-1 in 5.0 molL-1sulfuric acid) . Add 125 mL of water to a 500 mL conical flask. Carefully add 70 mL of concentrated sulfuric acid with constant swirling. Cool flask under cold water tap and add 0.75 g of potassium dichromate. Dilute to 250 mL with distilled water.

Starch indicator solution: (1.0% solution) Dissolve 1.0 g of soluble starch in 100 mL of recently boiled water. Stir until dissolved.

Sodium thiosulfate solution: (0.03molL-1). Add 7.44g of Na2S2O3.5H2O to a 1L volumetric flask, dissolve in distill water and dilute up to the mark.

Potassium iodide solution: (1.2molL-1) Dissolve 5 g of Kl in 25ml of water.

METHOD: [32

Ethanol sample suspended over acidified potassium dichromate solution.

 

 

 The left flask shows the brown-coloured solution resulting from the formation of iodine. The right flask shows how the brown colour fades to pale yellow as the iodine is titrated with thiosulfate (this is the stage at which starch solution should be added).

 

 

Upon addition of starch the solution takes on a blue-black colour due to the formation of a starch-iodine complex.

 

 

 

As more thiosulfate is added and we near the titration endpoint, the blue-black colour from the starch-iodine complex fades.

 

 

 

The endpoint of the titration is reached when just enough thiosulfate is added to react with all the iodine present and the solution becomes colourless

RESULT CALCULATIONS[32

The blank titration tells you how much acid dichromate was present at the start. As no alcohol was added the full amount of the dichromate is still present. The blank titrations are carried out so the result can be compared with those of the sample titrations.

1. Determine the average volume of sodium thiosulfate used for your sample from your concordant sample results.

2. Determine the average volume of sodium thiosulfate used for the blank titration from your concordant blank results.

43. Subtract the volume of the sodium thiosulfate solution used for the sample titration from the volume used for the blank titration. This volume of the sodium thiosulfate solution is now used to determine the alcohol concentration.

4. Calculate the number of moles of sodium thiosulfate in this volume.

5. Using the equations, determine the relationship between the moles of sodium thiosulfate and the moles of ethanol.

– as 6 mol of S2O32- is equivalent to 1 mol of Cr2O72-– and 2 mol of Cr2O72- is equivalent to 3 mol of C2H5OH– then 1 mol of S2O32- is equivalent to 0.25 mol of C2H5OH

6. Use this ratio to calculate the moles of alcohol in the sample solution.

7. Remember to allow for the dilution factor eg. if the dilution was 1:20 the result needs to be multiplied by 20.

8. Convert the answer in moles per litre to percentage (grams per 100mL) to compare with the figure given on the bottle of the alcoholic beverage tested.

IMPORTANCE OF REDOX REACTIONS

Oxidation-reduction reactions are vital for biochemical reactions and industrial processes. The electron transfer system in cells and oxidation of glucose in the human body are examples of redox reactions. Redox reactions are used to reduce ores to obtain metals, to produce electrochemical cells, to convert ammonia into nitric acid for fertilizers, and to coat compact discs.[28]

APPLICATIONS OF REDOX REACTIONS:

Redox titration have been used to quantify the mixtures of primary, secondary and tertiary amines. [24]

Used for studying sulphonamides, mixture of purines and for many other organic amino compounds and salts of organic acid. [24]

Redox reactions are normally strongly exothermic, and can make excellent candidates for thermometric titrations. [34]

redox reaction is useful in classical determination of ferrous ion with permanganate and the determination of hydrogen peroxide by permanganate titration. [34]

In the determination of hypochlorite (for example in commercial bleach formulations), a direct titration with thiosulfate can be employed. [34]

Thermometric iodometric titrations employing thiosulfate as a titrant are also practical, for example in the determination of Cu(II). [34]

Formaldehyde can be determined in electroless copper plating solutions by the addition of an excess of sodium sulfite solution and titrating the liberated hydroxyl ion with standard acid. [34]

o H2C=O + HSO3− + H2O → [HO-CH2-SO3

−] + OH−

ANALYTICAL METHODS

AMPEROMETRY:Hence, these measurements may be employed effectively to record the alteration in concentration of an ion in question in the course of a titration, and ultimately the end point is established. This specific process is commonly referred to as amphoteric method or amperometry.[25](discussed previously) POLAROGRAPHY:Hence it is based on the measurement of current resulting from reduction of an electro active species, at a given electrode potential under controlled condition.[30]

CAULOMETRY:Electrochemical method based on the quantitative oxidation or reduction of analyte. It is based on measurement of amount of electricity required to convert analyte to different oxidation state.It can be used for acid-base titrations, complexation titrations and can be used for redox titrations.[27]

CYCLIC VOLTAMMETRY:Cyclic voltammetry is the most widely used technique for accuring qualitative information about electrochemical reactions. The power of cyclic voltammetry results from its ability to rapidly provide considerable information on the thermodynamics of redox processes and the kinetics of heterogeneous electron transfer reactions and on coupled chemical reactions or adsorption processes. 27]

KARL FISCHER TITRATION OF H2O:Karl Fischer titration is the analysis method of choice for water content and

moisture determination in different samples. The spectrum ranges from raw materials through cosmetics, pharmaceuticals, foodstuffs and plastics up to gaseous samples.It essentially make use of karl fischer reagent which is composed of iodine, sulphur dioxide, pyridine and methanol.[31]

IODOMETRY:The iodimetry or iodimetric titrations include those titrations in which the

standard iodine soloution as oxidant is directly titrated with some reducing agent. It may therefore, be employed for the determination of reducing agents a.g. thiosulphates, sulphites, arsenties and stannous chloride etc. by titrating them against standard iodine solution.[31]

CERIMETRY:Ceric ion is a powerful oxidizing agent and titration procedure employing this

oxidant is called Cerimetry. In this present experiment ferrous ions are oxidized by ceric ions.26

Ce4+ + Fe2+ Ce3+ + Fe3+ . [29]

REFERENCES

1) http://books.google.com.pk/books?id=pGh6afAR2joC&pg=PA793&dq=define+titration&hl=en&sa=X&ei=IysiUtClA4a1tAay9IAY&ved=0CD8Q6AEwAw#v=onepage&q=define%20titration&f=false

2) http://books.google.com.pk/books?id=7VApthyH9yoC&pg=PA401&dq=titration+definition&hl=en&sa=X&ei=OzIiUrOFPNCO7QbnuYCQCA&ved=0CCsQ6AEwAA#v=onepage&q=titration%20definition&f=false

3) http://www.scribd.com/doc/25357952/Types-of-Titration4) http://www.scribd.com/doc/25357952/Types-of-Titration5) https://suite101.com/a/different-types-of-titration-and-indicators-a3685856) https://suite101.com/a/volumetric-analysis-and-titration-a3685587) http://www.fpharm.uniba.sk/fileadmin/user_upload/english/Physical_Chemistry/

Titration.pdf8) http://liakatas.org/chemblog/wp-content/uploads/2008/07/titration-and-back-

titration-handout.pdf9) http://www.titrations.info/titration-basic-terms10) Petrucci, et al. General Chemistry: Principles & Modern Applications. 9th ed.

Upper Saddle River, New Jersey: Pearson/Prentice Hall, 2007.11) Charles E. Ophardt, Virtual CHEMBOOK, c. 2003.12) Mc Alister, Applications of Aqueous Equilibria, 2011, Chp 1613) John E. McMURRY, Robert C. FAY, CHEMISTRY, Chp 15,Application of

Aqueous Equilibria – 5th edn ,pg593-59514) J. Oremusová, Manual for laboratory practice in physics for students of

pharmacy,2007, pg 315) The International Pharmacopoeia, fourth edition, 3rd supplement, 2013,

Methods of Analysis-sec 2.6, Non Aq. Titration.16) http://wiki.answers.com/Q/

When_does_a_neutralization_reaction_occur_in_everyday_life17) Richard Myers, The Basics of Chemistry, 01-Jan-2003, page 164.18) Neutralization Reaction - Acids + Bases Romanian Translation by Alexander

Ovsov19) http://www.scienceclarified.com/A-Al/Acids-and-Bases.html#ixzz2dRCoeNHz20) Basic concepts of analytical chemistry by S.M Khopkar chapter 6 page 4221) Advance chemistry by Michael Clugston, Rosalind Flamming page 21822) Ionic Equilibria In Analytical Chemistry by Jean-Louis burgot page 27723) Advanced Inorganic Chemistry Vol-1  By Gurdeep Rai page no 1346

24) Method of Analysis and Assay: Non-Aqueous Titrations. Dr. M. Shahar Yar.

Faculty of Pharmacy, Jamia Hamdard, Hamdard Nagar, New Delhi.

25) Pharmaceutical drug analysis by Ashotosh kar. Chapter no. 5, non aqueous

titration.

26) hmc.usp.org/sites/default/files/documents/HMC/GCs-dfs/c541%20USP36.pdf

27) Analytical electrochemistry by Joseph Wang.28) S Steenken - Chemical Reviews, 1989 - ACS Publications

29) University of chemistry Vol I. by C. Parameshwara Murthy.

30) Pharmaceutical analysis. Volume II. Dr. Anees Ahmed Siddiqui.

31) A text book of chemistry practicals Vol II by Walter Del Mar

32) Textbook of Quantitative Chemical Analysis,î 5th ed, GH Jeffery, J Bassett, J

Mendham, RD Denney, ìVogelís 1989, Wiley, NY

33) S steenken - chemical reviews, 1989 - acs publications

34) Bark, L. S. and Bark, S. M.; (1969). Thermometric titrimetry. International

Series of Monographs in Analytical Chemistry Vol 33 Pergamon Press (Oxford)