CHAPTER XXIX THE ALKALINE EARTH METALS 176. Calcium hydroxide. a. Place some small pieces of marble on a piece of wire gauze and apply a strong heat for about fifteen minutes. When cool, drop the residue into 25 cc. of water and stir. Then filter the liquid and divide the filtrate into two parts. Blow exhaled air through one portion (R). Add 1 or 2 drops of ferric chloride to the other portion (R). What other hydroxides would be precipitated by calcium hydroxide? b. Place about 10 cc. of clear limewater in a test tube and conduct carbon dioxide into the solution. What is the precipitate (R)? Continue the process until the precipitate dissolves (R). Divide the solution into two parts. Boil one part for a few minutes (R). What is temporary hardness? Prepare a dilute solution of soap and shake it vigorously in a test tube. Does it form a froth (lather)? Add to it some of the second portion of the solution and again shake. Does it still form a lather? What is the precipitate? 177. Calcium chloride. Dissolve 10 g. of marble in hydrochloric acid (R). What does the effervescence indicate? Marble is likely to contain a little carbonate of magnesium and of iron. What would become of these? Add an excess of limewater (R) and filter. Evaporate the solution to a volume of not more than 10 cc. and allow it to crystallize. What is the formula of the crystals? Drain off the mother liquid and evaporate it to dryness. What is the composition of the residue? Expose a small piece of it to the air for an hour and account for the results. Dissolve the crystals in a little water and divide the solution into two portions. To one portion add a few drops of ammonium carbonate (R); to the other add a few drops of solutions of ammonium hydroxide and disodium phosphate (R). 178. Calcium sulfate. a. Heat a crystal of gypsum in a test tube (R). Place on a glass plate some metal object, such as a file, which has been smeared with a drop of oil. Pour over the object a thick paste prepared by adding water to plaster of Paris. Set it aside until it hardens, then remove the object and note the result. What causes the paste to harden? For what is plaster of Paris used? b. Shake 1 g. of calcium sulfate with 10 cc. of water in a test tube, filter, and divide the solution into two parts. Test one part for the presence of sulfates. Is calcium sulfate soluble in water? Shake the other part with 1 or 2 cc. of soap solution. Does a froth form? How could such a solution be softened? Distinguish between temporary and permanent hardness of water. To what is each due? 179. Barium chloride. Weigh out accurately in a porcelain crucible from 1 to 2 g. of small crystals of barium chloride. Place the lid on the crucible and heat the crucible gently for a few minutes, holding the burner in the hand and moving it about so as to apply the heat uniformly. Finally, apply a strong heat for five minutes. When the crucible is cool, weigh. The residue is BaCl,. From your results determine the number of molecules of water of hydration in the crystals. 180. Analytical reactions. Place in separate test tubes solutions of a compound of each of the following elements: calcium, barium, strontium. Test the effect of each on the flame by means of a platinum wire, as in § 174. Add a few drops of a solution of potassium dichromate to each. Test the solubility of the precipitates in acetic acid. Add an equal volume of a saturated solution of calcium sulfate to solutions of each, heat to boiling, and set aside until cool. Note all the results. How could you distinguish between compounds of the three elements? |