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PRINCIPLES OF QUALITATIVE ANALYSIS. 119

c. To 20 c.c. cane sugar solution in a beaker add 2 c.c. of concentrated hydrochloric acid, and heat gently to boiling for fifteen minutes over the wire gauze. Cool, and neutralize the acid with solid sodium carbonate; then test with Fehling's solution. Result?

d. Repeat b and c, using 20 c.c. starch solution (make it as in Experiment LI, d) instead of cane sugar. Results?

EXPERIMENT LXXXVII.

SOME PRINCIPLES OF QUALITATIVE ANALYSIS.

Apparatus.Funnel, funnel support, beaker, test tubes. Materials. Solutions of nitrates of iron (ferric), silver, copper, barium, and sodium; hydrochloric acid, hydrogen sulphide, dilute sulphuric acid, ammonia water, filter papers, and two or more unknown substances.

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a. Qualitative Analysis is a system of experiments for the separation and identification of the elements present in mixtures of substances. In a limited sense the term is applied to the detection of the ordinary metals and acids. The separation of metals present as ions in a solution is possible if we can convert some of the metals into insoluble compounds while leaving the others in solution. The following experiments show how a scheme of analysis may be devised for the separation of the five metals: silver, copper, iron, barium, and sodium. We use solutions of the nitrates, since these are all soluble. Make ferric nitrate, if this is not found in the laboratory, by covering about 1 gram of iron wire or filings with 10 c.c. of water in a beaker and adding 10

c.c. dilute nitric acid in small portions. When action ceases, filter the solution and dilute it to 60 c.c.

b. To 5 c.c. of each of the nitrates named in a add dilute hydrochloric acid-one cubic centimeter at a time - until there is an excess. To know if you have an excess of the precipitant let the precipitate settle, and add a drop more of the precipitant to the clear solution; or filter a little of the precipitated solution and test the filtrate in the same way. (Cf. § 246, last two paragraphs.) Be sure that your test tubes are clean for every test.

Copy the following table in your note book, and put down the results in their places.

Effect of AgNO3 Cu(NO3)2 Fe(NO3)3 Ba(NO3)2 NaNO3

HCI

H2S

H2SO4

NHẠOH

c. Treat 5 c.c. of each of the solutions named in a with hydrogen sulphide in excess. Make sure you have an excess, as suggested in b. Tabulate your results. Be sure the tube delivering the gas is clean before every test. For the action of hydrogen sulphide with ferric salts, cf. Experiment LXXII, g. For the conversion of ferrous ions into the ferric state, see Experiment LXXII,

d.

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d. Treat 5 c.c. of each of the five solutions with an excess of dilute sulphuric acid, and tabulate the results.

PRINCIPLES OF QUALITATIVE ANALYSIS. 121

e. Repeat d, using ammonium hydroxide solution in place of sulphuric acid.

f. From the results tabulated in b to e devise a plan for identifying any one of the five nitrates, and of separating them, if they are all present in a mixture.

g. From previous experiments tell how you would determine whether a white, soluble solid given you was sodium chlorate, nitrate, sulphate, carbonate, sulphite, acetate, or thiosulphate? .

h. If you wished to make a mixture of copper and barium salts, would you use copper sulphate? Why? Why not use barium chloride or ferric chloride solution if you wish to get a soluble mixture of the ions of these metals and those of silver?

i. Get from the teacher two or more unknown substances, and determine what metal or metals of the five named are present; also what acid.

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