Non-aqueous titration

Non-aqueous titration

Non-aqueous titration

points to be covered:-

1.Defination & theory

2.Reasons for non-aqueous titration

3.Solvents used in non-aqueous titration

4.Types of non-aqueous titration

5.Estimation of sodium benzoate

6.Estimation of ephedrine HCL

 

DEFINITION & THEORY :-

-water is commonly used as a solvent in most of the titrations but the limitation occurs for eg if the reactant is insoluble in water/ reactant is reactive with water/analyte (sample) is either too weak acid/ too weak base.

-because of too weak acids/bases are not titrated in aqueous solution due to amphoteric behaviour of water(i.e water can react as an acid on titration with a base and act as a base on titration with acids. hence water is not suitable for titration to overcome this problem water is replaced with another non-aqueous solvent so this type of titration is known as non-aqueous titration.

REASONS FOR NON-AQUEOUS TITRATION

-the reactant is insoluble in water

-the reactant is reactive with water

-the sample is to weak acid/base


SOLVENTS USED IN NON-AQUEOUS TITRATION

PROTOGESIC SOLVENTS

these are acidic solvents and used to enhance the basicity of weak bases.

e,g. glacial acetic acid (anhydrous/water-free acetic acid is sometimes called as glacial acetic acid because it solidifies just below room temp at 16.7°C

PROTOPHILIC SOLVENTS

these are basic solvents and used to enhance the acidity of weak acids.

e,g. pyridine, ethylenediamine & dimethylformamide(DMF)

AMPHOTERIC SOLVENTS

these solvents behave as acid as well as a base depending on the substance dissolved in it.

they can accept or donate protons.

e,g. alcohol

APROTIC SOLVENTS

these solvents neither accept a proton nor donate proton

e,g. benzene, carbon tetrachloride


some example are discussed below

GLACIAL ACETIC ACID

-most commonly used solvent

-before used for titration check the water content insolvent.

-water level insolvent is may be between 0.1 to 1%

ALCOHOL

-mostly used in combination of alcohol and other for e,g. combination of ethylene glycol with propane-2-ol or butane-1-ol.

-the combination provides admirable solvents for both the polar and non-polar end of the molecules.

-e,g. salts of organic acids, especially of soaps are best determined in a mixture of glycols & alcohols or a mixture of glycols and hydrocarbon.

DIOXANE

-commonly used for non-aqueous titration in place of glacial acetic acid when a mixture of substances is to be qualified

-separate endpoints are normally possible, corresponding to the individual components in a mixture

DIMETHYL FORMAMIDE;- (DMF)

-DMF is protophilic solvents

-frequently-used because the endpoint is difficult to obtain


TYPES OF NON-AQUEOUS TITRATIONS;-

1.ACIDIMETRY

it involves the quantitative determination of weak bases by non-aqueous titration.

2.ALKALIMETRY

it involves the quantitative determination of weak acids by non-aqueous titration.


ESTIMATION OF SODIUM BENZOATE

 

for estimation following steps are taken

1.preparation of 0.1N solution of HCLO4 and its standardization

-dissolve 8.5ml of 72% hclo4 in about 900ml glacial acetic acid with constant stirring, add about 30ml acetic anhydride and make up the volume (1000ml) with glacial acetic acid & keep the mixture for 24hr acetic anhydride absorbed all the water from hclo4 & glacial acetic acid & renders the solution virtually anhydrous.

-HCLO4 must be well diluted with glacial acetic acid before adding acetic anhydride because the reaction between HCLO4 & acetic anhydride is explosive.

2.standardisation of HCLO4

-to 500mg of potassium acid phthalate add 25ml of glacial acetic acid & few drops of 5% w/v crystal violet in glacial acetic acid as an indicator this solution is titrated with 0.1HCLO4.

the colour changes from blue to blue-green.

3.assay procedure

-weight accurately about 0.25g of sodium benzoate dissolved in 20ml of anhydrous glacial acetic acid, warming to 50dee/c if necessary, cool titrate with 0.1m perchloric acid, using 0.05ml of 1-naphtholbenzen solution as indicator carry out a blank titration.

4.equivalent/I.P factor

1ml of 0.1M perchloric acid is equivalent to 0.0144gm of C7H5NaO2.5.calculation.

%sodium benzoate = x ml  × normality × 100/  N (given)  × weight of sample (in gm)

where

X ml= volume of titrant consumed at endpoint

normality calculated= normality of perchloric acid after standardisation.

normality given= 0.1N (theoretically)


ESTIMATION OF EPHEDRINE HCL

1.preparation of 0.1N solution of HCLO4 & its standardization

-dissolve 8.5ml of 72% hclo4 in about 900ml glacial acetic acid with constant stirring. add about 30ml acetic anhydride and make up the volume (1000ml) with glacial acetic acid and keep the mixture for 24hours. acetic anhydride absorbed all the water from HCLO4 & glacial acetic acid & renders the solution virtually anhydrous HCLO4 must be well diluted with glacial acetic acid before adding acetic anhydride because the reaction between HCLO4 & acetic anhydride is explosive.

2.standardisation of HClO4

to 500mg of potassium acid phthalate, add 25ml of glacial acetic acid & add few drops of 5% w/v crystal violet in glacial acetic acid as an indicator. this solution is titrated with 0.1 HclO4.

the colour changes from blue to blue-green.

3.assay procedure

-weight accurately about 0.17gm of ephedrine HCL, dissolve in 10ml of mercuric acetate solution. warming gently add 50ml of acetone & mix. titrate with 0.1M perchloric acid, using 1ml of a saturated solution of methyl orange in acetone as indicator until the red colour is obtained. carry out a blank titration.

4.equivalent/I.P factor –

1ml of 0.1m of 0.1M perchloric acid is equivalent to 0.02017g of C10H15NO3.HCL

5.CALCULATION

% ephedrine HCL =  X ml  × normality  × 0.02017  × 100/ N (given )  × weight of sample (gm)

X ML= volume of titrant consumed at the endpoint

normality calculated=normality of perchloric acid after standardization

normality given = 0.1N (theoretically)

{NOTES BY: MS. MAYURI MACHHINDRA LENDAVE ( B.PHARMA) ( PROFESSOR)}

B pharm sem book set


Conductometry

Wikipedia,

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