THE RUDOLF REPORT

GERMAR RUDOLF · THE RUDOLF REPORTof no importance to our investigation.B: According to the literature, the dissociation behavior of acids asa function of temperature is not unanimous. 353 Although there is a tendencyof increasing protolysis 354 with rising temperature, this tendencyturns upside down at higher temperatures for some acids, others showgenerally falling values. Since the changes are generally in the range oflow percentages only, and because speed of protolysis is generally veryhigh, hence never a restricting factor, this can be neglected here.6.5.5. pH ValueThe pH value (acidity) influences the formation in various ways.In chapter 6.5.1., reference has already been made to the higher reductionpower of cyanide and iron(III)-cyanide in alkaline environment.The pH value also influences the reactivity of iron compounds in thesolid body (chapter 6.5.3.).As remarked above, dissolved hydrogen cyanide hardly exhibitsreactivity. The formation of cyanide ions by absorption and dissociationof hydrogen cyanide only starts in sufficient degree at neutral pHvalues and above, see Graph 4. 355 The data leading to Graph 4, togetherwith the data that enabled us to plot Graph 2 (saturation concentrationof HCN as a functionof temperature), leads 100to a graph revealing therelationship betweentemperature, pH value(acid content), and CN –saturation concentration,see Graph 5 (at aconcentration of 1mol% HCN in air,which is approximately1% by weight, theusual disinfestationdissociation degreeof HCN [%]80604020050% at pH 9.31 = pKA of HCN5 6 7 8 9 10 11 12 13pH-valueGraph 4: Degree of disassociation ofhydrogen cyanide as a function of the pH valueat room temperature.353 R.C. Weast (ed.), op. cit., (note 322), p. D 163.354 Protolysis is the splitting of acids (HAc) into their corresponding acid anion (base, Ac – ) andproton (H + , or with water to H 3 O + ): HAc + H 2 O Ac – + H 3 O +here HCN + H 2 O CN – + H 3 O + ..355 pK A values of HCN: 9.31; R.C. Weast (ed.), op. cit. (note 353).168