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1.确定出在0.2％准确度范围内KCNS溶液标定的实难条件: (1)剧烈摇荡时以KCNS溶液滴定AgNO_3溶液,Fe~(3+)浓度为0.01-0.1M。 (2)通常摇荡时以AgNO_3溶液滴定KCNS溶液,Fe~(3+)浓度为0.05-0.3M。 (3)热凝沉淀时以KCNS溶液滴定AgNO_3溶液,Fe~(3+)浓度为0.01-0.2M。 2.与计算值对比表明,硫氰酸银严重地吸附银离子,在各种条件下吸附是难以避免的,实践上应该控制的是程度问题卽取得补偿结果。剧烈摇荡5分钟的终点除Fe~(3+)低浓度外并未达到化学平衡,甚至热凝条件下,CNS~-有分解趋势的情况下也并未到反应式的定量进行。 3.解释了文献与专论中关于Volhard测定氯化物法中指示剂浓度计算值与实际值的矛盾。
1. Determine the actual conditions of KCNS solution calibration within the accuracy of 0.2%: (1) titrate the solution of AgNO 3 with KCNS solution at a concentration of 0.01-0.1 M Fe 3+ under vigorous shaking. (2) The KCNS solution is usually titrated with AgNO 3 solution with a Fe 3+ concentration of 0.05-0.3M. (3) Titration of AgNO_3 solution with KCNS solution at the concentration of Fe ~ (3+) of 0.01-0.2 M during thermocoagulation precipitation. Compared with the calculated value, silver thiocyanate adsorbed silver ions seriously, under various conditions, adsorption is unavoidable. In practice, the extent of the problem should be controlled so as to obtain the compensation result. The end of 5 minutes of vigorous shaking did not reach the chemical equilibrium except for the low concentration of Fe ~ (3+). Even under the condition of thermal coagulation, the decomposition trend of CNS ~ - did not reach the quantitative reaction. 3. Explain the inconsistencies in the literature and monographs regarding the calculated and actual values of the indicator concentrations in Volhard’s determination of chloride.