The purpose of the standard is intended to provide preparation and standardization procedure of standard solution
2. SCOPE
This procedure is applicable to the standard solutions used for food analysis in the chemical department.
3. RESPONSIBILITY
Chemist authorized for preparing and standardization of standard solution
4. PROCEDURE
4.1 EDTA (sodium salt) 0.01 N
4.1.1 Preparation-
2 grams of EDTA and 0.05 gram of magnesium chloride hexahydrate in water and dilute to a volume of 1 liter
4.1.2 Standardization
Standardize the solution against 0.01N calcium chloride (0.566 g dried and dissolved in 1000ml distilled water) using the Eriochrome-T indicator for calcium and magnesium estimation. For calcium use ammonium purpurate indicator
4.1.3 Calculation- N1 V1 = N2 V2
Where N1 =normality to be known
N2 =normality of CaCl2
V1 =volume of EDTA used
V2 =volume of CaCl2 taken
4.2 Ferrous ammonium sulfate (FAS) 0.25 M
4.2.1 Preparation-
Dissolve 98 grams of ferrous ammonium sulfate in 400 ml of water. Add 20 ml of concentrated sulfuric acid and dilute to 1000 ml.
4.2.2 Standardization-
Take 12.259 grams of potassium dichromate previously dried at 1030C for 24 hours and dissolve in distilled water and dilute it to 1000ml. Add 120 mg of sulphamic acid.
Take 25 ml of this solution in a conical flask dilute about 100ml add 30ml concentrated sulfuric acids and
Cool and titrate with FAS using 2-3 drops of ferroin indicator.
4.2.3 Calculation-
Volume (in ml) of
0.04167M K2Cr2O7 x 0.25
Volume (in ml) of FAS required
4.3 Iodine solution 0.1 N
4.3.1 Preparation-
12.7 grams of resembling iodine in a 250 ml beaker, then add 25 grams of iodate-free potassium iodide. add 25 ml water in it to dissolve it completely and makeup up 1000 ml with distilled water. Store the solution in an amber-colored glass stoppered bottle.
4.3.2 Standardization-
Take 25 ml of iodine solution in a 250 ml iodine flask and dilute to 100 ml with water. Titrate it against 0.1N sodium thiosulphate solution (25 grams of sodium thiosulphate dissolve in 1000 ml water) from a burette until the color is reduced to pale yellow color. Add 2 ml of starch solution and continue the titration until the blue color of the solution change to a colorless solution.
4.3.3 Calculation- N1 V1 = N2 V2
where N1 = normality to be known
V1 = volume taken of iodine solution
N2 = normality of sodium thiosulphate
V2 = titrate volume sodium thiosulphate
4.4 Silver Nitrate (AgNO3) 0.1 N
4.4.1 Preparation-
Dissolve 16.9873 grams of silver nitrate in water and dilute to 1000 ml with chloride-free Distilled water. Store in an amber-colored glass-stoppered bottle.
4.4.2 Standardization-
Weigh accurately about 0.1 grams of sodium chloride, previously dried at 1100C for 2 hours, and dissolve in 50 ml of CO2-free water. Add a few drops of potassium chromate indicator solution and titrate against silver nitrate until a faint but distinct reddish brown color persist after vigorous shaking
4.4.3 Calculation- Weight of NaCl x 1000 x Purity
of NaCl
Volume of AgNO3 used x 58.44 100
4.5 Sodium hydroxide (NaOH) 1 N
4.5.1 Preparation-
Dissolve 42 grams of NaOH in sufficient carbon dioxide-free water and dissolve in 1000ml.
4.5.2 Standardization-
Weigh accurately about 5 grams of potassium hydrogen phthalate previously dried at 105+50C for 2hr and dissolve in 75 ml of CO2-free water. Add 0.1 ml phenolphthalein indicator and titrate with sodium hydroxide solution. The permanent pink color is obtained.
4.5.3 Calculation- Weight of KHP x 1000 x Purity
of KHP
The volume of NaOH used x 204.22 100
4.6 Sodium thiosulphate (Na2SO3) 0.1 N
4.6.1 Preparation-
Dissolve 25 grams of sodium thiosulphate (Na2S2O3.5H2O) in CO2-free water and dilute to 1000 ml with the same water.
4.6.2 Standardization-
i. Weigh about 5g of Potassium dichromate previously dried at 105oC + 2 o C till constant weight. Dissolve in water and makeup up 1 ltr. Take aliquot 25ml in an iodine flask. Add 5ml conc HCl and 15 ml of 10% potassium iodide solution. Allow standing in dark for 5 min. Titrate with sodium thiosulphate solution using the starch indicator, until the blue color disappears.
N
= 25 W
49.03 V where W= weight
in mg of Potassium dichromate
V= volume in ml of sodium thiosulphate
used
ii. Dissolve
approx. 1.5 grams of Potassium dichromate (previously dried at 120oC
for 4 hours), weighed accurately in sufficient water to produce 250 ml. To 25 ml
of this solution add 2 grams of potassium iodide and 8 ml of conc. HCl acid gently mixes and titrates with sodium thiosulphate solution until the blue color
disappears.
4.6.3 Calculation- Weight of K2Cr2O7
x 1000 x Purity of K2Cr2O7
Volume
of Na2SO3 used
x 49.03 100
4.7.1 Preparation-
Transfer 3 ml of sulfuric acid into a volumetric flask containing about 500 ml of water. When cool dilute to 1000 ml
4.7.2 Standardization- Transfer 25 ml of standard 0.1 N sodium hydroxide solution into a 250 ml conical flask. Titrate with the sulfuric acid solution using the phenolphthalein indicator.
N1 V1 = N2 V2
where N1 = normality of sodium thiosulphate
V1 = volume taken of iodine solution
N2 = normality to be known
V2 = titrate volume sodium thiosulphate
or, DRY Sodium carbonate at 260+ 10oC for 1 hr and cool. Take approx. 150mg sodium carbonate in 70 ml CO2-free water. Titrate with methyl orange indicator.
4.7.3 Calculation- Weight of Na2CO3
x 1000 x Purity of Na2CO3
Volume of H2SO4 used
x 52.99 100
4.8 Hydrochloric acid (HCl) 0.1 N
4.8.1 Preparation-
Transfer 9 ml of hydrochloric acid into a 1000 ml volumetric flask containing about 500 ml of water. When cool dilute to 1000 ml.
4.8.2 Standardization- Transfer 0.100g approx. sodium carbonate previously dried at 260oC + 10 oC for 1 hr. Dissolve in 50-70 ml CO2-free water. Titrate sodium carbonate solution with 0.1N HCl using methyl orange indicator, the endpoint appears orange to faint pink color.
4.8.3 Calculation- Weight of Na2CO3
x 1000 x Purity of Na2CO3
The volume of HCl used x 52.99 100
· IS 2316: 1990
· IS 13574: 1992
· APHA
6.0 REVISION/CHANGE HISTORY
7.0 RECORD
Logbook -Reagent preparation for titrimetric analysis
Logbook -Standard preparation
8.0 ATTACHMENTS: NA
END OF DOCUMENT
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