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These metals all combine directly and rapidly with the halogens, and with sulphur. The following compounds of these metals have been gasified and their molecular weights determined, KI, RBI, RECI, RbI, CsCl, CsI; in these molecules the atoms of potassium, rubidium, and caesium are monovalent.
The five elements we are now considering form the family 436 of alkali metals ; the prominent chemical characteristics of these metals have been already examined in Chap. XI. pars. 163–168. It will suffice to summarise these characteristics here.
Oxides and hydroxides, M,0 and MOH, are strongly basic and alkaline; very soluble in water, M,0 forming MOHAq. The hydroxides are formed at ordinary temperatures by direct interaction of oxides M, with water; they are not decomposed by heat alone. Oxides of rubidium and caesium have not yet been isolated. The oxides Na O, K,O and a few others, are known.
Sulphides and hydrosulphides, M.S and MSH, are strongly basic; they interact with many more negative sulphides to form thio-salts. No sulphide of rubidium or caesium has yet been isolated. M,S,, MS, MS, MS, are known, where M = Na or K.
Haloid compounds, MX, are very stable solids, soluble in, and not decomposed by, water. The chlorides, except LiCl, form many double compounds with chlorides of less positive elements, e.g.
PtCl . 2MCI; SbC1.6MCI. Salts, M.X where X = SO, 2NO,, C0g, 2010PO, &c. are very definite, stable, bodies; very few basic salts exist. Many of the salts combine with similar salts of less positive elements forming double salts; the alums M SO..X,380,.24H,O are important (X = Al, Cr, Fe, Ga, In). Lithium does not form an alum. Most of the salts are easily soluble in water.
Lithium is less like the other members of the family than they are like each other. LiOH is much less soluble in water than the other hydroxides; Li CO and Li PO, are also much less soluble than the other carbonates and phosphates ; Li,SO does not combine with Al,.350, a double salt 3 Li,SO,.Cr,(SO.) is known, but it is not an alum. All the elements of the family except lithium form sulphates of the form MHSO, ; Li H (SO2), is known.
The odd-series elements of Group I. shew great differences 437 in their physical and chemical properties; sodium is evidently closely allied to the even-series members; hydrogen must be considered apart from the other elements, copper, silver, and gold exhibit resemblances but also marked differences.
leable; very good con- ductile; good conductor ductile; very tenacious;
Crystallises in regular and electricity.
frequently with similar quently with Cues, silver, and frequently compounds of silver, Sb2S3, &c.; AgÕI also also with small quantiiron, &c. Fairly widely occurs. Most lead ores ties of copper and iron. distributed and in con- contain small quanti- Compounds of gold do siderable quantities. ties of silver.
not occur. Prepared by roasting Widely distributed, Widely distributed, Cu s in air till mixture generally in compara- generally in small of CuO and Cu2S is pro- tively small quantities. quantities. duced, then shutting off Prepared by heating Preparing by washing air and raising tempera- Ag2S with salt in air away gangue &c., someture, when Cu2S+2CuO (Ag2S + 2NaCl +40 times by mixing crushed =4Cu + SO2.
=Na2SO4+2 AgCl), auriferous quartz and then agitating with with mercury whereby iron (2AgCl + Fe a gold-amalgam is =FeCl2+2Ag). formed, and then re
moving Hg by heating. General chemical Oxidised to Cuo by Slowly oxidised by di- Not oxidised by direct properties. strongly heating in air. rect union with oxygen union with oxygen.
Combines directly with at very high tempera- Combines directly with
but a few salts are ob-
General formulae and chemical characters of compounds. The only compounds which have been gasified and the vapourdensities of which have been determined are Cu Cl, and AgCl. The following formulae are not necessarily molecular.
Copper forms two series of compounds, represented by the following ; (1) Cu,0, Cu,Ci,, Cu,SO,; (2) Cuo, Cuci,,
Cuso. Silver forms one series of compounds represented by Ag, o, Ag, Cl,, Ag,SO
Gold forms two series, represented by, (1) Au, 0, Au,cl,, (2) Au, Oz, Au,cl, or AuCl.z.
A hydride of copper, Cu, H,, is known.
Oxides. MO where M = Cu, Ag, Au; MO where M = Cu, . Ag, Au; M.O, where M = Au only.
Sulphides. M S where M = Cu or Ag; MS where M = Cu; M,S, where M = Au.
Haloid compounds. M,Cl, where M = Cu, Ag, Au; MCI, where M=Cu; MCI, where M = Au.
Salts. Most of the copper salts belong to the form CuX where X =SO, 2NO,, CO, PO, 2010, &c.; a few are known of the form Cu X. The definite silver salts all belong to the form Ag, X. Very few salts of gold are known; some seem to be similar in composition to the silver salts and to be represented by the formula Au X, others belong to the form Au,3X.
The compositions of the compounds of copper silver and gold may be represented by the following general formulae; X=0, S, Cl, Bre, 1,, SO, 2003, 2NO3, PO, &c.
The oxides MO are prepared ; in the case of Ag,0 by 439 adding potash or soda to a solution of a salt of silver (e.g. 2AgNO, Aq + 2KOHAq = Ag, 0 + 2KNO, Aq + H,O); in the cases of Cu O and Au, by reducing solutions of copper or gold salts in the presence of an alkali, CuSO, Aq may be reduced by grape sugar, and AuCl Aq by sulphur dioxide.
Cuprous oxide Cu,o is fairly stable, but it is easily oxidised to CuO by heating in air; with acids it forms cupric salts, e.g. CuSO,; the cuprous salts, which correspond to Cu,o,
are not obtained from the oxide. Argentous oxide, Ag,0, is a stable compound which interacts with acids to form salts and water; e.g. Ag,0 + 2HNO, Aq=2 AgNO Aq+H,0; it is decomposed at about 250° to silver and oxygen. This oxide is strongly basic, in some of its reactions it closely resembles the oxides of the alkali metals; an hydroxide of silver has not however been isolated. Aurous oxide, Au,0, is very easily decomposed; it rapidly absorbs oxygen with formation of auric oxide Au,0,: one or two salts corresponding to Au, O are known, but they are not obtained from the oxide; the oxide is said to be soluble in cold water.
The oxides MO are prepared; CuO by adding an alkali to the solution of a cupric salt, and heating the hydrated oxide CuO.H.O which is precipitated (e.g. CuSO, Aq + 2KOHAq= CuO.HO+K SO Aq; and CuO.HO heated, even in contact with water, =ČuO+H,O); Ago by passing ozonised oxygen over finely divided silver; Auo by heating hydrated auric oxide, Au,Og.H,O, to 160°.
Cupric oxide CuO is basic, it interacts with acids to form a large series of salts CuX(X = SO, &c.); this oxide is not decomposed by heat alone; most reducing agents remove the oxygen from heated Cuó. The oxide does not combine directly with water, but the hydrate CuO.HO is obtained, indirectly, as described above. Argentic oxide, or silver peroxide, Ago (or Ag,0) is easily decomposed; heated to 110° it suddenly evolves oxygen and silver remains; this oxide interacts with acids to form argentous salts (e.g. Ag SO, Ag2NO,, &c.) and oxygen, that is, it behaves as a peroxide.
Auro-auric oxide Auo (Au), is usually known as auric oxide) is easily decomposed; at 1730 it is separated into gold and oxygen; it does not appear to form any salts by reacting with acids.
Auric oxide, Au,0g, the only representative of the M,Og class of oxides, is prepared by adding an alkali to a solution of auric chloride Aucl, (magnesia seems to be the best alkali to use), drying the precipitated Au,0,H,O, and then carefully heating it to 100°. The oxide is easily decomposed by heat, or by exposure to light; it dissolves in nitric acid, and the salt Au(NO3)3.HNO,.36,0 can be obtained from this solution; it interacts with hydrochloric acid to form the compound AuClHCl, and with hydrobromic acid to form AuBr HBr; these compounds are monobasic acids forming salts such as KAuCl, and KAuBr.. Hydrated auric oxide, Au,0,. H,O,
acts an acid towards strong alkalis; it dissolves in concentrated KOHAq, and the salt potassium aurate KA_0,.3H,0 may be obtained by evaporating in vacuo.
The sulphides M S (M=Cu or Ag) are obtained by the 440 direct union of the elements, or in the case of Ag S by precipitating a solution of a silver salt by hydrogen sulphide. When hydrogen sulphide is passed into a solution of a salt of copper, cupric sulphide, Cus, is precipitated. The two sulphides of gold, AuS and Au Sy, seem to be obtained by the interaction of hydrogen sulphide with solution of auric chloride, AuCl2, under varying conditions.
The sulphides Cu S, CuS, and Ag, S interact with acids to form salts and hydrogen sulphide, cupric salts being obtained from both sulphides of copper. Both sulphides of gold, Aus and Au,Sz, dissolve in solutions of alkali sulphides to form thio-salts, the salts NaAuS and KAus, having been obtained ; these sulphides are therefore acidic.
The haloid compounds M,X, M=Cu, Ag, Au, are 441 obtained; in the case of copper and gold by reducing the compounds CuX; in the case of silver by the interaction of haloid acids with silver oxide Ag, O. Cu,
Cl, is formed by heating a solution of Cuci, in HČIAq with copper, or with sulphur dioxide, and pouring into water; Au,cl, is produced by dissolving gold in aqua regia, evaporating to dryness, and heating cautiously. By the interaction between Aucl, and hydriodic acid, aurous iodide, Au I, is obtained
(2AuCl Aq + 6HIAq=Au, I, + 40 + 6HClAq). Cuprous iodide is formed by reducing CuSO Aq by sulphur dioxide and adding potassium iodide solution.
The haloid compounds of silver, AgCl, AgBr, Agl, are very stable compounds; Cu,CI, has been gasified; Cu I, is also a stable compound; Au CI, is separated into its elements by heat or by the action of reducing agents.
The only representatives of the class of haloid compounds MX, are the cupric compounds. Cupric chloride, CuCl,, is obtained from the corresponding oxide, Cuo, by dissolving in HCIAq, and evaporating. This chloride combines with ammonia to form various compounds CuCl ..NH, it also combines with alkali chlorides to form double salts, e.g. CuCl,. 2KCI.2H,0. Various oxychlorides are also derived from CuCl,; their composition may be expressed by the general formula xCuCl,. yCuO.