Volumetric Solutions Preparation and Standardization

Volumetric solution, also known as standard solution, is a solution that precisely prepared to have a known concentration of a specific substance and is commonly used in volumetric analysis to determine the concentration of other solutions. In the realm of chemistry and laboratory work, volumetric solutions play a crucial role in various scientific experiments and analyses with their accurate measurements and reliable properties, ranging from medicine to environmental science. Volumetric solutions may be prepared by dissolving accurately weighed primary standard chemicals to make an accurately known volume of solution. Or it can be prepared by roughly weighing a certain amount of a substance or measuring a certain volume of a solution and then formulating them into a solution close to the desired concentration and finally standardized by primary standards solutions or already-standardized solutions. The latter is suitable for the preparation of most volumetric solutions. The accuracy of many analytical procedures is dependent on the manner in which such solutions are prepared and standardized. Here, the procedure for preparations and standardization of typical and common volumetric solutions with specific concentrations is summarized according to the report ^[1].

Preparation and Standardization

Note:

The preparation of volumetric solutions involves applying traditional chemical analysis techniques. It is validated that the employed apparatus is accurate in order to make sure it is suitable for the intended application.
The volumetric solution should be standardized in a medium with a similar composition to the one it will be employed in.
Because the results obtained by titration analysis depend on the reliability of the volumetric solutions used, it is imperative that the latter be standardized at least in triplicate with particular care and preferably by experienced analysts.

Acetic Acid, 1 N

Add 61 g (58.1 mL) of glacial acetic acid to a 1 L volumetric flask, dilute to volume with water, and mix thoroughly. Standardize as follows: Measure accurately 40 mL of the solution into a 250 mL conical flask, add 0.10 mL of phenolphthalein indicator solution, and titrate with freshly standardized 1 N sodium hydroxide volumetric solution to a permanent pink color.

Ammonium Thiocyanate, 0.1 N

Dissolve 7.61 g of ammonium thiocyanate in 100 mL of water. Transfer to a 1 L volumetric flask, dilute to volume with water, and mix thoroughly. Standardize as follows: Measure accurately 40 mL of freshly standardized 0.1 N silver nitrate volumetric solution into a 250 mL conical flask containing 50 mL of water. Add 2 mL of nitric acid and 2 mL of ferric ammonium sulfate indicator solution. While stirring, titrate with ammonium thiocyanate solution to the first appearance of a red-brown color

Cupric Sulfate, 0.1 M

Dissolve 24.97 g of cupric sulfate pentahydrate in 500 mL of water. Transfer to a 1 L volumetric flask, dilute to volume with water, and mix thoroughly. Standardize as follows: Using a 50 mL burette, measure 40.0 mL of the cupric sulfate solution into a 250 mL beaker. From a burette, add 45.0 mL of freshly standardized 0.1 M EDTA and 50 mL of methanol. Stir magnetically, and using a pH meter, adjust the pH of the solution to 5 with saturated aqueous ammonium acetate. Maintain the pH between 5.1 and 5.3 throughout the titration. Add 0.1 mL of PAN indicator solution, and continue to titrate with the 0.1 M copper sulfate volumetric solution to a permanent blue end point.

EDTA, 0.1 M

Dissolve 37.22 g of Na₂EDTA · 2H₂O in 500 mL of water. Transfer quantitatively to a 1 L volumetric flask, dilute to volume with water, and mix thoroughly. Standardize as follows: Weigh accurately 0.40 g of calcium carbonate, previously dried at 210 °C for 4 h. Transfer to a 400 mL beaker, and add water. Cover the beaker with a watch glass, and introduce 4 mL of hydrochloric acid (1:1) from a pipette inserted between the lip of the beaker and the edge of the watch glass. Swirl the contents of the beaker to dissolve the calcium carbonate. Wash down the sides of the beaker and the watch glass with water, and dilute to 200 mL. While stirring, add from a 50 mL burette about 30 mL of the EDTA standard solution. Adjust the solution to pH 12–13 with 10% sodium hydroxide, and add 300 mg of hydroxy naphthol blue indicator mixture. Continue the titration with the EDTA volumetric standard solution to a blue end point.

Ferrous Ammonium Sulfate, 0.1 N

Dissolve 39.21 g of ferrous ammonium sulfate hexahydrate in 200 mL of 25% sulfuric acid. Transfer quantitatively to a 1 L volumetric flask, dilute to volume with water, and mix thoroughly. On each day of use, standardize as follows: Measure accurately 40 mL of the solution into a 250 mL conical flask, add 0.1 mL of 1,10-phenanthroline reagent solution, and titrate with a freshly standardized 0.1 N ceric ammonium sulfate volumetric solution to the change from pink to pale blue.

Ferrous Sulfate, 0.1 N

Dissolve 27.80 g of clear ferrous sulfate heptahydrate crystals in about 500 mL of water containing 50 mL of sulfuric acid. Transfer quantitatively to a 1 L volumetric flask, dilute to volume with water, and mix thoroughly. On each day of use, standardize as follows: Measure accurately 40 mL of the solution into a 250 mL conical flask, add 60 mL of water, and titrate with freshly standardized 0.1 N potassium permanganate to a pink end point. Perform a blank titration using only water.

Potassium Dichromate, 0.1 N

Weigh accurately 4.90 g of potassium dichromate, previously dried for 2 h at 110 °C. Transfer to a 1 L volumetric flask, dilute to volume with water, and mix thoroughly. Standardize as follows: Measure accurately 40 mL of the solution into a 250 mL iodine flask, and add 100 mL of water, 3 g of potassium iodide, and 3 mL of hydrochloric acid. Stopper immediately, and allow to stand in the dark for 5 min. Titrate the liberated iodine with a freshly standardized 0.1 N sodium thiosulfate solution. Add 3 mL of a starch indicator solution near the end of the titration, and continue to the absence of the blue starch–iodine complex.

Potassium Iodate, 0.05 M (0.3 N)

Weigh exactly 10.70 g of potassium iodate, previously dried at 110 °C to constant weight, transfer to a 1 L volumetric flask, dilute to volume with water, and mix thoroughly. Standardize as follows: To 15.0 mL of solution in a 250 mL iodine flask, add 3 g of potassium iodide and 3 mL hydrochloric acid previously diluted with 10 mL of water. Stopper immediately, and allow to stand in the dark for 5 min. Then add 50 mL of cold water, and titrate the liberated iodine with freshly standardized 0.1 N sodium thiosulfate. Add 3 mL of starch indicator solution near the end of the titration, and continue to the absence of the blue starch–iodine complex.

Potassium Permanganate, 0.1 N

Dissolve 3.3 g of potassium permanganate in 1 L of water in a 1500 mL conical flask, heat to boiling, and boil gently for 15 min. Allow to cool, stopper, and keep in the dark for 48 h. Then filter through a fine-porosity sintered-glass filter, and place in a glass-stoppered amber bottle. Standardize as follows: Weigh accurately about 0.26 g of sodium oxalate (NIST SRM 8040), previously dried for 2 h at 105 °C, transfer to a 500 mL conical flask containing 250 mL of water and 7 mL of sulfuric acid, and heat to 70 °C. Titrate immediately with the permanganate solution to a pink color that persists for 15 s. The temperature at the end of the titration should not be less than 60 °C. Perform a blank titration containing 250 mL of water and 7 mL of sulfuric acid in the same manner, and subtract the volume of the potassium permanganate consumed in the blank from the first titration. Store in an opaque or amber glass container.

Potassium Thiocyanate, 0.1 N

Weigh exactly 9.72 g of potassium thiocyanate, previously dried for 2 h at 110 °C, transfer to a 1 L volumetric flask, dilute to volume, and mix thoroughly. Standardize as follows: Measure accurately 40 mL of freshly standardized 0.1 N silver nitrate volumetric solution into a 250 mL conical flask, and add 100 mL of water, 1 mL of nitric acid, and 2 mL of ferric ammonium sulfate indicator solution. Titrate with the thiocyanate solution, with agitation, to a permanent light pink-brown color of the supernatant solution.

Silver Nitrate, 0.1 N

Weigh exactly 16.99 g of silver nitrate, previously dried for 1 h at 100 °C, transfer to a 1 L amber volumetric flask, dilute to volume, and mix thoroughly. Standardize as follows: Weigh accurately about 0.33 g of potassium chloride (NIST SRM 999) ignited at 500 °C. Place in a 250 mL beaker, and dissolve in 100 mL of water. Add 2 mL of dichlorofluorescein indicator solution. With stirring, titrate with silver nitrate solution until the silver chloride flocculates and the mixture acquires a faint pink color. Store in an opaque container.

Sodium Hydroxide, 1 N

Dissolve 162 g of sodium hydroxide in 150 mL of carbon dioxide-free water, and cool the solution to room temperature. Prepare a 1 N solution by diluting 54.5 mL of the concentrated solution to 1 L with carbon dioxide-free water. Mix thoroughly, and store in a tight polyolefin container. Standardize as follows: Weigh accurately about 8.5 g of potassium hydrogen phthalate, acidimetric standard (NIST SRM 84), previously lightly crushed and dried for 2 h at 120 °C. Dissolve in 100 mL of carbon dioxide-free water, add 0.15 mL of phenolphthalein indicator solution, and titrate with the sodium hydroxide solution to a permanent faint pink color.

Sodium Thiosulfate, 0.1 N

Dissolve 24.82 g of sodium thiosulfate pentahydrate and 200 mg of sodium carbonate, anhydrous, in 1 L of recently boiled and cooled water, and mix thoroughly. Allow to stand for 24 h, and standardize as follows: Weigh accurately about 0.21 g of NIST potassium dichromate, oxidimetric standard (NIST SRM 136), previously crushed and dried at 110 °C for 2 h. Dissolve in 100 mL of water in a glass-stoppered iodine flask. Swirl to dissolve the sample, remove the stopper, and quickly add 3 g of potassium iodide, 2 g of sodium bicarbonate, and 5 mL of hydrochloric acid. Insert the stopper, swirl slightly to release excess carbon dioxide, cover the stopper with water, and allow to stand in the dark for 10 min. Rinse the stopper and the inner walls of the flask with water and titrate the liberated iodine with the sodium thiosulfate until the solution becomes faintly yellow. Add 3 mL of starch indicator solution, and continue the titration to the disappearance of the blue starch–iodine complex. Restandardize the solution frequently.

Zinc Chloride, 0.1 M

Weigh accurately 6.54 g of zinc (13.63 g of ZnCl2), and dissolve in 80 mL of 10% hydrochloric acid. Warm if necessary to complete dissolution, cool, dilute with water to volume in a 1 L volumetric flask, and mix thoroughly. Standardize as follows: Pipette and transfer 40.0 ml of zinc chloride solution to a 400 mL beaker with sufficient hexamethylene tetramine to produce a purple-red color. Titrate with freshly standardized 0.1 M EDTA to a color change of purple-red to lemon yellow.

Reference

Volumetric Solutions. ACS Reagent Chemicals, Part 3. DOI:10.1021/acsreagents.3003.

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