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10, PV A TEXT BOOK OF PHARMACEUTICAL ANALYSIS-I, STANDARDIZATION, Standardization means, determination of strength of a given sample solution and can be, determined by reacting the solution quantitatively with a standard solution., Standard may be of two types:-, 1. Primary standard:- Primary standard is a solution of known strength made from the, substance of high purity, which satisfy following conditions:-, 1. It should be highly stable., 2. It should be obtained in pure state., 3. It should have high molecular weight., 4. It should be of high solubility i.e. readily soluble in water., Examples of primary standards used for titration of acids are:-, Sodium carbonate:- Na,CO3, mol wt. = 105.99 g/mol, Tris-(hydroxymethyl)aminomethane (THAM):- (CH2OH);CNH2, mol wt. =, 121.14 g/mol, Examples of primary standards for titration of bases are:-, Potassium hydrogen phthalate (KHP):- KHC8H4O4, mol wt. = 204.23 g/mol, Potassium hydrogen iodate:- KH(IO3)2, mol wt. = 389.92 g/mol, Oxalic acid:- CH2O4, mol wt. 90.03488 g/mol, Examples of primary standards for redox titrations are:-, Potassium dichromate:- K2Cr,07, mol wt. = 294.19 g/mol, Sodium oxalate:- Na2C,O4, mol wt. = 134.00 g/mol, 2. Secondary standard:- Secondary standard is a solution of known strength which is previously, standardized by a primary standard. For example:- Standard solution of 0.1 M sodium, hydroxide, standard solution of 0.1 N sulphuric acid etc., PREPARATION AND STADARDIZATION OF SOLUTIONS, In volumetric analysis, solutions are needed to be accurately prepared to minimize errors in, results. Preparation and standardization of some commonly used solutions in volumetric, analysis is described here under:-, 1. PREPARATION OF OXALIC ACID (0.1 N):- Weigh accurately about 6.3 mg of oxalic acid and, dissolve in 1000 ml of distilled water. Oxalic acid is a primary standard therefore there is no, need to standardize it., Scanned with CamScanner
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PHARMACEUTICAL ANALYSIS, 11, 2. PREPARATION AND STANDARDIZATION OF POTASSIUM PERMANGANATE SOLUTION (0.1N):-, Principle:- In redox titrations, strength of an oxidizing agent is estimated by titrating it with a, reducing agent and vice-versa. Potassium permanganate acts as an strong oxidizing agent in, acidic medium that oxidizes oxalic acid into carbon dioxide. Known strength of oxalic acid is, titrated directly with potassium permanganate. End point can be detected with appearance of, permanent pink colour, potassium permanganate acts as self indicator. Reaction involved in this, titration is as follows., K,SO, +, Potassium, 10CO2, 2KMNO4 + SH,C,04 + 3H,SO4, Sulphuric, 2MNSO4 + 8H,0, Manganese, sulphate, Potassium, Oxalic, Water, Carbon, permanganate, acid, acid, sulphate, dioxide, Preparation of potassium permanganate solution (0.1 N):- Weigh accurately about 3.2 g of, potassium permanganate and dissolve in 1000 ml of distilled water, then heat on water-bath for, 1 hour, allow to stand for 2 days and filter it through a funnel containing plug of glass wool., NOTE:- Store the prepared solution in dark coloured bottle i.e. protected from light., Standardization of potassium permanganate solution (0.1 N), 1. Clean and dry all glassware as per standard laboratory procedure., 2. Take 500 ml of unknown stock solution of potassium permanganate in a clean and dry, beaker., 3. Rinse the burette with distilled water. Then, pre-rinse it with a portion of the potassium, permanganate solution before you fill it up for the titration. Pre-rinsing is necessary to, ensure that all of the solution in the burette is the desired solution, not a diluted or, contaminated solution., To do this, add about 10 ml of the potassium permanganate solution to the clean burette., Carefully turn the burette on its side so the liquid slowly runs out the top. Rotate the, burette on its axis during this time to make sure the solution wets the sides all the way to, the top. Pour the rinse from the burette into a waste beaker. Repeat the rinsing process, with a second portion of the potassium permanganate solution., 4. Take 20 ml of prepared oxalic acid solution in a conical flask., 5. Add 5 ml of sulphuric acid., 6. Warm the mixture to about 70°C., 7. Then fill the burette with potassium permanganate solution., 8. Start titration with the potassium permanganate solution until reach the endpoint. The, approach of the endpoint is suggested by the temporary appearance of a pink colour that, fades when the solution is swirled for upto 10 seconds. A pink colour that persists for more, than 30 seconds signals the actual endpoint., Scanned with CamScanner
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12, PV A TEXT BOOK OF PHARMACEUTICAL ANALYSIS-I, Note:- The solution may lose its colour after 30 seconds or more, but it is not considered., 9. Record the reading of burette., 10. Repeat the titration three times to get precise readings., 11. Take mean of them and calculate normality of potassium permanganate solution., 3. PREPARATION OF SODIUM THIOSULPHATE (0.1 N):-, Principle:- When known strength of potassium iodate is reacted with excess potassium iodide in, acidic condition, results in liberation of iodine. Liberated iodine is titrated directly with sodium, thiosulphate. End point can be detected with disappearance of permanent blue colour due to, conversion of iodine into sodium iodide. Reaction involved in this titration is as follows., 3K,SO4, 312, 3H,0, 3H,SO4, Sulphuric, KIO;, 5KI, Potassium, Potassium, Potassium, Iodine, Water, iodate, iodide, acid, sulphate, → Na,S,O6, Sodium, 2Na,S,O3, 2Nal, Iodine, Sodium, Sodium, thiosulphate, tetrathionate, iodide, Preparation of sodium thiosulphate (0.1 N):- Weigh accurately about 24.8 g of sodium, thiosulphate (Na,S2O3.5H20) and dissolve it in 200 ml of freshly boiled and cooled water. Shake, the content for 2 minutes and make up the volume upto 1000 ml., Standardization of sodium thiosulphate (0.1 N), 1. Clean and dry all glassware as per standard laboratory procedure., 2. Take 500 ml of unknown stock solution of sodium thiosulphate in a clean and dry beaker., 3. Rinse the burette with distilled water. Then, pre-rinse it with a portion of the sodium, thiosulphate solution before you fill it up for the titration. Pre-rinsing is necessary to ensure, that all of the solution in the burette is the desired solution, not a diluted or contaminated, solution., To do this, add about 10 ml of the sodium thiosulphate solution to the clean burette., Carefully turn the burette on its side so the liquid slowly runs out the top. Rotate the, burette on its axis during this time to make sure the solution wets the sides all the way to, the top. Pour the rinse from the burette into a waste beaker. Repeat the rinsing process, with a second portion of the sodium thiosulphate solution., 4. Take 10 ml of prepared potassium iodate solution in an iodine flask., 5. Add 2 g of potassium iodide and 5 ml of dilute sulphuric acid in it., 6. Keep the flask in dark for 10 minutes., Scanned with CamScanner
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PHARMACEUTICAL ANALYSIS, 13, 7. Add 2 to 3 drops of starch indicator., 8. Then fill the burette with sodium thiosulphate solution., 9. Start titration with the sodium thiosulphate solution until reach the endpoint. The approach, of the endpoint is suggested by the change of a blue colour to colourless., 10. Record the reading of burette., 11. Repeat the titration three times to get precise readings., 12. Take mean of them and calculate normality of sodium thiosulphate solution., 4. PREPARATION AND STANDARDIZATION OF CERIC AMMONIUM SULPHATE (0.1 M):-, Principle:- Ceric ammonium sulphate solution is titrated with primary standard arsenic trioxide, in the presence of sulphuric and osmic acid using ferroin sulphate as an indicator. End point can, be detected by change in colour from pink to very pale blue. Reaction involved in this titration is, as follows., As,O3, NaOH, NaAsO,, Arsenic trioxide, Sodium hydroxide, Sodium arsenite, NaAsO2, 2H,0, NaH2AsO4 + 2H* + 4e, Sodium arsenite, Water, Sodium arsenate, 4 x [Ce+ + e, Ce* ], Preparation of ceric ammonium sulphate (0.1 M):- Weigh accurately about 65 g of ceric, ammonium sulphate [Ce(NH4)a(SO.)a.2H20] and dissolve it in a mixture of 30 ml sulphuric acid, and 500 ml water with gentle heat. Cool and filter the solution, then make up the volume upto, 1000 ml., Standardization of ceric ammonium sulphate (0.1 M):-, 1. Clean and dry all glassware as per standard laboratory procedure., 2., Take 500 ml of unknown stock solution of ceric ammonium sulphate in a clean and dry, beaker., 3. Rinse the burette with distilled water. Then, pre-rinse it with a portion of the ceric, ammonium sulphate solution before you fill it up for the titration. Pre-rinsing is necessary to, ensure that all of the solution in the burette is the desired solution, not a diluted or, contaminated solution., To do this, add about 10 ml of the ceric ammonium sulphate solution to the clean burette., Carefully turn the burette on its side so the liquid slowly runs out the top. Rotate the, Scanned with CamScanner
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14, PV A TEXT BOOK OF PHARMACEUTICAL ANALYSIS-I, burette on its axis during this time to make sure the solution wets the sides all the way to, the top. Pour the rinse from the burette into a waste beaker. Repeat the rinsing process, with a second portion of the ceric ammonium sulphate solution., 4. Weigh accurately about 0.2 g of arsenic trioxide (previously dried at 105°C for 1 hour) and, transfer it to 500 ml conical flask., 5. Add 25 ml of sodium hydroxide solution (8.0% w/v) in it and swirl to dissolve., 6. Add 100 ml distilled water and mix properly., 7. Add 30 ml dilute sulphuric acid, 0.5ml osmic acid solution and ferroin sulphate solution and, mix properly., 8. Then fill the burette with ceric ammonium sulphate solution., 9. Start titration with the ceric ammonium sulphate solution until reach the endpoint. The, approach of the endpoint is suggested by the change of a pink colour to very pale blue., 10. Record the reading of burette., 11. Repeat the titration three times to get precise readings., 12. Take mean of them and calculate molarity of ceric ammonium sulphate solution., 13. Equivalent factor of Arsenic trioxide for 0.1 M ceric ammonium sulphate is 0.004946., 5. PREPARATION AND STANDARDIZATION OF HYDROCHLORIC ACID (0.1M):-, Principle:- Known strength of sodium carbonate is titrated directly with hydrochloric acid. End, point can be detected by using methyl orange or methyl red as an indicator. Reaction involved in, this titration is as follows., 2HCI, 2NaCl, H,0, + CO2, Na,CO3, Sodium, Hydrochloric, Sodium, Water, Carbon, acid, chloride, dioxide, carbonate, Preparation of HCI (0.1 M):- Take 8.5 ml of Hydrochloric acid and dilute upto 1000 ml with, distilled water., Standardization of hydrochloric acid (0.1 M):-, 1. Clean and dry all glassware as per standard laboratory procedure., 2. Take 500 ml unknown stock solution of HCI in a clean and dry beaker., 3. Rinse the burette with distilled water. Then, pre-rinse it with a portion of the HCl solution, before you fill it up for the titration. Pre-rinsing is necessary to ensure that all of the solution, in the burette is the desired solution, not a diluted or contaminated solution., To do this, add about 10 ml of the HCI solution to the clean burette. Carefully turn the, burette on its side so the liquid slowly runs out the top. Rotate the burette on its axis during, this time to make sure the solution wets the sides all the way to the top. Pour the rinse from, Scanned with CamScanner
