United States or Samoa ? Vote for the TOP Country of the Week !
The preparation of an approximately tenth-normal solution of the reagent may be carried out as follows: PROCEDURE. Dissolve about 3.25 grams of potassium permanganate crystals in approximately 1000 cc. of distilled water in a large beaker, or casserole. Heat slowly and when the crystals have dissolved, boil the solution for 10-15 minutes.
The sublimed iodine is then dried by placing it in a closed container over concentrated sulphuric acid. It may then be weighed in a stoppered weighing-tube and dissolved in a solution of potassium iodide in a stoppered flask to prevent loss of iodine by volatilization. About 18 grams of the iodide and twelve grams of iodine per liter are required for an approximately tenth-normal solution.
Since both solutions are approximately tenth-normal, 35 cc. of the bichromate solution may be added without testing. If a blue precipitate appears at once, 0.5 cc. of the bichromate solution may be added before testing again. The stirring rod which has touched the indicator should be dipped in distilled water before returning it to the iron solution.
Such solutions are called !Normal Solutions! and contain such an amount of the reacting substance per liter as is equivalent in its chemical action to one gram of hydrogen, or eight grams of oxygen. Solutions containing one half, one tenth, or one one-hundredth of this quantity per liter are called, respectively, half-normal, tenth-normal, or hundredth-normal solutions.
As the thiosulphate in crystalline form has the formula Na S O .5H O, this weight is 248.12 grams. Tenth-normal or hundredth-normal solutions are generally used. !Approximate Strength, 0.1 N! PROCEDURE. Weigh out on the rough balances 13 grams of commercial iodine. Place it in a mortar with 18 grams of potassium iodide and triturate with small portions of water until all is dissolved.
This is particularly true if, in connection with the normal solution, the weight of substance for analysis is chosen with reference to the atomic or molecular weight of the constituent to be determined. The preparation of an !exactly! normal, half-normal, or tenth-normal solution requires considerable time and care.
Word Of The Day