AND SALTS.] NaOH + NaHS0 4 = Na 2 S0 4 Sodium Sodium hydrogen Sodium hydroxide. sulphate. sulphate. CHEMISTRY OH, 487 Water. Salts derived from acids by the partial displacement of their hydrogen are termed acid salts, those in which the hydrogen displaceable by metals is entirely displaced being termed normal salts. Similarly, when the hydrogen in polyacid hydroxides is entirely displaced by negative radicles, normal salts are obtained, but when it is only partially displaced the so-called basic salts are produced, which bear precisely the same relation to the hydroxides that the acid salts bear to the acids. Thus, from the triacid hydroxide, bismuth hydroxide, Bi "(OH) 3 , and the mono basic acid, nitric acid, we obtain normal bismuth nitrate and two basic bismuth nitrates : Bi (N0 3 {N0 3 (N0 3 Normal salt. N(X Bi 4 NO N0 3 Bi <{ OH OH" I OH Basic salts. These sales are strictly comparable with the normal and two acid salts produced from the tribasic acid, phosphoric acid, and the mouacid hydroxide, sodium hydroxide : ( ONa ( ONa ( ONa PO { ONa PO { ONa PO ^ OH . I ONa (OH (OH Normal salts. Acid salts. Two explanations may be given of the constitution of the salts formed by displacing the hydrogen in polybasic acids by polyad elements ; the formula of barium sulphate, for example, may be represented by either of the following formulae : QO / R c;n /O.Ba.O S0 2 j >Ba, S0 2Jo.Ba.O according as it is supposed that two atoms of hydrogen in a single molecule of the acid are displaced, or that two mole cules of the acid are concerned in the formation of the salt, one atom of hydrogen in each being displaced by each of the barium atoms. There is not at present sufficient evidence to enable us to decide definitively in favour of one or the other of these views, but the great tendency which the polybasic acids exhibit to form double salts appears to render the latter the more probable. The formation of salts by the action of acids on metallic oxides and hydroxides is in all cases attended with a development of heat. This subject has been very care fully studied by several chemists, especially by Thorns sn, whose results for a number of acids are given in the follow ing tables. The amount of heat developed in the re action aNaOHAq , Q Aq , that is to say, on adding a solution of a molecules (in grammes) of sodium hydroxide to a solution of one mole cule (iu grammes) of the acid, represented by Q, is given for a number of acids in the first of the following tables. The second table exhibits the amount of heat developed in the reaction NaOHAq , aQAq ; i.e., on adding a solution of one molecule of sodium hy droxide to a solution of a molecules of the acid Q. Each molecule (in grammes) of sodium hydroxide was dissolved in 200 molecules (in grammes) of water, and the solutions of the acids were of equivalent strength ; that is to say, the number of grammes of acid required to form a normal salt with 23 + 16 + 1 or 40 grammes of sodium hydroxide were dissolved in 18 x 200 or 3600 grammes of water. The temperature at which the two solutions were mixed in all the experiments was about 18 C. The results are expressed in hundreds of heat-units, and according to Thomsen they may all be relied on within 1 per cent. (aNaOHAq.QAq). Q=l molecule. <* Name of Acid. Formula. i i 2 3 289 205 4 c 273 206 416 353 374 554 Monobasic Acids. Hydrochloric Hydrobromic H.CI H.Br H.I H.F H.SH H.CN H.OC1 H.N0 3 H . PH 2 2 H . PO.j H . CH 2 H . C 2 H 3 2 H a .SiF 6 H 2 . PtCL H 2 . S0 4 H 2 . SeO 4 68-5 68-5 63 80 39 14 49 68 77 71 66" 71 137 137 137 163 77 28 96 137 152 144 132 132 138 136 146 148 131 159 148 148 110 111 43 137 137 137 163 78 27 96 137 153 133 266 272 310 304 247 290 270 271 284 202 200 52 272 310 304 292 293 275 206 54 96 285 244 527 Hydriodic Hydrofluoric Hydrosulphuric Hydrocyanic Hypochlorous Nitric Hypophosphorous. . Metaphosphoric Formic Acetic Dibasic Acid.i. Hydrottuosilicic Hydroehloroplatinic Sulphuric Selenic Chromic . . H 2 . Cr0 4 Sulphurous H 2 . SO, Selenious. . H 2 . Se0 3 Dithionic H 2 .S 2 6 H 2 .PH0 3 H 2 .C0 3 H 2 . B 2 4 H 2 . Si0 3 H 2 . Sn0 3 H,.C 2 4 Ho.CJLO, 74" 64 32 Phosphorous Carbonic Boric Silicic Stannic Oxalic 69 138 124 124 283 242 253 250 271 276 286 258 382 340 359 Succinic . Tartaric H S .C 4 H 4 O 6 ... Tribasic Acids. Citric H,.C fl H B 7 Phosphoric H 3 -P0 4 H a . As0 4 H 4 .P 2 7 73 74 144 Arsenic Tetrabasic Acids. Pyrophosphoric (XaOHAq.aQAq). Q=l molecule. a Name of Acid. Formula. 2 l i i i i Monobasic Acids. Hydrochloric H.CI H. Br H.I H.F H . SH H.CN H.N0 3 H . PH 2 3 H.P0 3 H . CH0 2 H . CgH-jOj H s . SiF 6 H 2 . PtCl 6 H 2 . S0 4 H 2 . Se0 4 H 2 . Cr0 4 H 2 .S0 3 H 2 . Se0 3 H 2 .S 2 6 H 2 .PH0 2 K 2 . C0 3 H 2 .B 2 4 H 2 . Si0 3 H 2 . Sn0 3 H 2 . C 2 4 H 2 .C 4 H 4 4 H 2 . C 4 H 4 O 6 H 3 . C 6 H 8 7 H 3 .P0 4 H, . As0 4 H, . P,0 7 137 137 136 160 77 28 136 154 142 132 142 149 129 65 138 147 147 137 137 137 13 77 28 137 152 144 132 132 133 136 146 148 131 159 148 148 110 111 43 138 124 124 124 148 150 144 68-5 68-5 68-5 8? 39 14 68 76 66 133 136 155 152 124 145 135 135 142 101 100 26 141 121 127 125 135 138 143 96 68 86 127 113 120 68 78 76 63 73 69 51 135 24 71 61 132 46 84 69 59 62 91 Hydrobromic Hydriodic Hydrofluoric Hydrosulphuric H y drocyanic Nitric Hypophosphorous. . . Metaphosphoric Formic Acetic Dibasic Acids. Hydrofluosilicic Hydroehloroplatiiiie Sulphuric Selenic Chromic Sulphurous Selenious Dithionic Phosphorous Carbonic ... Boric Silicic Stannic Oxalic Succinic Tartaric Tribasic Acids. Citric Ph osphoric ...... Arsenic Tetrabasic Acids.
Pyrophosphoric ....Page:Encyclopædia Britannica, Ninth Edition, v. 5.djvu/499
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