of crystallized carnallite. Which of these are hydrated? Weigh out the required amount of magnesium chloride and about one third more than the required amount of potassium chloride, mix the salts, and dissolve them in the least possible volume of hot water. Allow the solution to cool, decant the mother liquor, and wash the crystals with a very little cold water. See if you can detect both magnesium and potassium in the crystals. Is this a double salt or a complex salt? CHAPTER XXXII THE IRON FAMILY 192. Reactions of the ferrous ion. a. Place about 1g. of iron in a beaker and cover the material with water. Iron by alcohol dissolves the fastest, but tacks or clean turnings will do. Add dilute hydrochloric acid, a small portion at a time, so as to keep up a brisk evolution of gas (R). Note the odor. It is chiefly due to phosphine; how do you account for the presence of this substance? Note the choking effect of the gas when breathed. Hold a nonluminous flame over the beaker for a moment. How do you account for the flashes of light? Before the iron has all dissolved, filter and at once make the following tests, using 1 or 2 cc. for each. b. Try the action of a solution of ammonium sulfocyanate (NH CNS). Pass hydrogen sulfide into a little of the solution (R). Test the action of ammonium sulfide (R). How do you account for the difference in the results of the last two experiments? Add sodium hydroxide to some of the solution (R). What is the color of the precipitate? What change occurs after the contents of the test tube have stood exposed to air (R)? 193. Ferrous ammonium sulfate. Dissolve 10 g. of iron in dilute sulfuric acid and filter from the insoluble residue (what is it?). What weight of ferrous sulfate should be in the filtrate? Dilute it to about 50 cc. What would be an equimolecular weight of ammonium sulfate? Weigh out this amount and add it to the hot solution of ferrous sulfate. Set the beaker aside for the crystallization of the salt. Filter off the crystals, wash them with a very little cold water, and spread them on filter paper to dry. What is the formula? 194. Reactions of the ferric ion. a. As in § 192, dissolve about 1 g. of iron in dilute hydrochloric acid and then treat the solution with 3 or 4 cc. of aqua regia. (What does this produce (R)?) Use portions of the resulting solution for the experiments below. b. To one portion of the solution obtained in a add ammonium hydroxide in excess (R). To another portion add sodium hydroxide (R). Is the product soluble in an excess of the reagent? Test a third portion with a solution of ammonium sulfocyanate (R). To a fourth add sodium carbonate in excess. What is the precipitate (R)? To a fifth portion add ammonium sulfide in excess. Is the product ferric sulfide (R)? How can you tell? Dissolve some of the precipitate in hydrochloric acid. The milky residue is sulfur. Can you account for it? c. Boil the remainder of the solution prepared in a, with the addition of hydrochloric acid, until the aqua regia has been destroyed. Then add about half a gram of zinc, warming the whole to maintain a brisk evolution of hydrogen. What change in color do you note? From time to time test small portions with ammonium sulfocyanate, adding more zinc if necessary. What inference do you draw? d. If you dissolve a little iron in nitric acid, would you expect to obtain a ferric salt or a ferrous salt? Try it. Obtain a crystal of ferric nitrate, put it in a test tube, and add a little water. How do you explain the result? Since nitric acid is a strong acid, how would you describe ferric hydroxide ? Dissolve 10 g. of crystals 195. Ferric ammonium sulfate. of ferrous sulfate in 20 cc. of water. amount of sulfuric acid necessary to convert the salt to the ferric state; then add nitric acid, a drop at a time, until the color no longer changes. Evaporate (hood) to a sirupy mass and dissolve in a little hot water. Add to the resulting solution the amount of ammonium sulfate necessary to form ferric ammonium sulfate, and heat gently until the salt is dissolved. Set the resulting solution aside to crystallize. |