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BARIUM OXIDE AND BARIUM HYDR OXIDE 199

Note 9 6), page 15). These crystals are efflorescent, hen ce, assoon as the pap er package is unw rapped, p lace th em in a 2-ouncecork-stoppered bott le .

QUESTIONS1. Exp la in why s t ron t ium carbona te, which is less soluble in

pure water than stront ium sulphate, should dissolve readi ly indilute acids, while the la tte r sa lt w ill dissolve scarcely any morein acids than in pu re water.

2. If a smal l quant i ty of a solution of s t ron t ium chloride wereadded to a solut ion containing equimolal quanti t ies of sodiumcarbonate and sodium sulp hate, wh at w ould be the precipi tateformed?

P R E PA R AT I O N 22

B A R I U M O X I D E AND B A R I U M H Y D R O X I D E F RO M

BARIUM CARBONATE, Ba OH) 2 -8H 2 O

The commercia l method of pre pa ring calcium oxide quicklime)consists in heat ing calcium carbonate l imestone) in lime kilns.Barium oxide might be mad e from bariu m carbo nate according

to the same principle, except for the fact th at the t empera tu rerequired for the decom posi t ion of bar ium carbonate is so high asto make such a metho d almost imp ract icable. This greaterstabi l i ty of the barium sal t is an i l lustration of the fact t ha t bariumoxide is even m ore strongly b asic th an calcium oxide. The reac-t ion , BaCO3 ? BaO + CO 2 , is reversible, and in common withother reversible reactions it may be made to progress in onedirection or the o the r by suitably altering the concentrat ion ofthe substances present in the react ing system . Of the threesubstances involved in this reaction the only one which can beremoved during the course of the reaction is the carbon dioxide.I t is, however, not enough to let it merely pass off as a gas, be-cause to escape from the crucible it will have to push back theatmosphere . The pressure of carbon dioxide in equilibrium withbar ium carbonate at 1350 is seen from the t ab le to be but one-half an a tmosph ere , tha t is to say, bariu m carbo nate will decomposeunt i l the a tmosphere in the crucible co ntains ab ou t 50 per cent of

carbon dioxide and then the decom position will sto p. How ever,at high temperatures charcoal reacts with carbon dioxide to formcarbon monoxide

C O2 + C 2CO

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ALKALI AND ALKALINE EARTH METALS

At the equilibrium point of this reaction the partial pressure ofcarbon monoxide is many times that of the carbon dioxide;thus it would be much above 1 atmosphere, and carbon monox-ide would escape from the crucible. W ith excess powdered char-coal in the crucible, therefore, both reactions would continueto run until all the barium carbonate had changed to bariumoxide. Carbon monoxide does not react with barium oxide.

In the following procedure, in addition to the charcoal, a littlerosin is mixed with the charge. On heating , the rosin decomposesforming finely divided carbon which becomes very intimatelymixed with the charge.

Temperature

700750800

897100011001350

Pressure of CO2 inequilibrium with

CaCO3

22 mm.80

167

7608740

BaCOs

2.7 mm.

381.

The barium oxide obtained in this way is not pure , but containsparticles of charcoal as well as impurities coming from the mineral.It is very suitable, however, for the manufacture of barium hy-droxide, into which it is converted by treatment with water.

Barium hydroxide is extremely soluble in hot water, but sparinglyso in cold water, from which it separates in flake-like crystals ofthe composition Ba OH )2-8H2O.

Materials barium carbonate, BaCO3, 99 grams = 0.5 F.W .; ifthe mineral witherite is used it should be veryfinely powdered; the artificially prepared m ate-rial will react more readily,

powdered charcoal, 25 grams,

rosin, 5 grams. pparatus gas furnace.30-gram clay crucible, with cover. inch porcelain dish.

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BARIUM OXIDE AND BARIUM HYDROXIDE 20 1

5-inch filter funnel and filter.5-inch w atch glass.500-cc. flask,iron ring and ring stan d.Bunsen burner.

Procedure Mix the f inely powdered barium carbonate with10 gram s of powde red charcoal and 5 gra m s of powdered rosin.After mixing the whole mass very thoroughly in a mortar, placeit in the crucible, press it down firmly, and cover it with a layerof charcoal at least \ in ch de ep. Pla ce a well-fitting cover on the

crucible and he at t h e whole for 1 ho ur in the gas furnace to ashigh a tem pe ra tu re as possible. After the crucible has cooled,remove the top layer of charcoal, place the barium oxide in theporcelain dish, and very cautiously add a few drops of water,noting th e ve ry violent reaction. Fin ally add 400 cc. of water,and heat the mixture in the dish to boiling; pour the solutionthro ug h a large, ord ina ry fil ter No te 4 c), pag e 7), lett ing th eclear liquid run directly into a 500-cc. flask and keeping the funnelcovered w ith a w atc h glass to pre ve nt cooling du rin g th e filtration.Rinse t he residue in th e dish with 75 cc. m ore of boiling wa ter, andpour this upon the fil ter after the first portion has nearly all runthro ug h. Sto pp er th e flask and allow th e solution to cool slowlyto room temperature; finally, cool i t nearly or quite to 0; collectthe crystals on a suction fil ter; wrap the product in paper towelsand leave it over nigh t to dry at room tem pe rat ur e N ote 9 6),page 15). P u t the pro du ct in an 8-ounce cork-stoppered bo ttle.

QUESTIONS

1. How does barium hydroxide become contaminated by ex-posu re to th e air? W hy m ight this pro du ct be dried w ith lesscontaminat ion by exposure to the air out-of-doors than to the airof the laboratory?

2. The mineral witheri te often contains barium sulphate asan im pu ri ty. Sta te w hat changes this substance would undergoduring the above process. How could bariu m hydroxide be p re-pared from bariu m sulphide? Com pare prep arat ion of s tron-t ium hydroxide from stront ium sulphate, page 194.)

3 . Devise a method for preparing barium hydroxide frombarium carbonate by which the use of a furnace may be avoided.

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2 0 2 ALKALI AND ALKALINE EARTH METALS

uggestion Make use of the difference in solubility of bariumchloride and barium hydroxide.

xp rim nts

Very few of the chemical properties of the non-metals are dis-played except in conjunction with the metals; in our study of thenon-metals in the preceding chapters, therefore, we already havehad revealed to us many of the chemical properties of the metals.

1. Pla ce a few sm all lum ps of m arb le calcium carbo-na te ) in a sm all porc elain crucible. Co ver th e crucible inorder to keep in the heat, and heat i t strongly for 20 minutesw ith a Bu nsen flame. W hen th e pro du ct has cooled, weteach lump with a single drop or two of water and wait a fewm inu tes , if neces sary, to observe th e effect. T he lum psshould grow ve ry ho t, and steam be driven off. Th en wetthe prod uct with somew hat m ore wa ter, and tes t the reactionof the moist mas s tow ard s li tm us. T he li tm us is coloredstrongly blue by the suspension.

It requires a bright red heat to decompose CaCO3 into CaOand CO2. T he CaO is a strongly basic oxide and combiness t rongly wi th water to form the base Ca 0H)2 , as is evidenced bythe heat evolved. C a 0 H )2 is sparingly soluble but enough dis-solves to color l i tmus strongly blue.

2. Place a few gram s of magnesium carb on ate in a 4-inchporcelain dish and hea t i t rath er m ode rately, tes ting t o see if

carbon dioxide is being expelled. Fro m tim e to t im e test th eresidue for carbonate by removing a l i t t le from the dish,thoroughly wetting it with about 5 cc. of hot water in a testtube , add ing acid, an d w atch ing for effervescence. Verygentle heating suffices to change the magnesium carbonateso that it no longer effervesces with dilute HC1.

In both calcium carbonate and magnesium carbonate, whichmay be formulated CaO-CO2 and MgO-CO2, we have the sameacid anhydride, CO2. Th e tenac i ty w ith which the basic an-hydrides CaO and MgO hold this acid anhydride is a measure oftheir basic stre ng th. M agnesium oxide is, therefore, less stronglybasic than calcium oxide.