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1、POTENTIOMETRIC DETERMINATION OF pHpH 值电位测定法The pH is a number which represents conventionally the hydrogen ion concentration of an aqueous solution.For practical purposes, its definition is an experimental one.The pH of a solution to be examined is related to that of a reference solution (pHs)by the
2、 following equation:in which E is the potential, expressed in volts, of the cell containing the solutionto be examined and Es is the potential, expressed in volts, of the cell containing thesolution of known pH (pHs), k is the change in potential per unit change in pH expressed in volts, and calcula
3、ted from the Nernst equation.其中， E 是待测溶液电势，单位伏特；Es 是已知 pH 溶液的标准电势,单位伏特； k 表示 pH 每变化一个单位的电势变化，从能斯特方程计算得来，单位伏特。Table Values of k at different temperatures表The potentiometric determination of pH is made by measuring the potential difference between 2 appropriate electrodes immersed in the solution to b
4、e examined: 1 of these electrodes is sensitive to hydrogen ions (usually a glass electrode) and the other is the reference electrode (for example, a saturated calomel electrode).pH 的电势测定是测定沉浸在待测溶液中的2 个适当电极之间的电位差：其中一个是氢离子敏感电极 ( 通常是玻璃电极) ，另一个是参比电极( 例如饱和甘汞电极) 。Apparatus.The measuringapparatusisa voltme
5、terwithan inputresistanceatleast100times that of the electrodes used. It is normally graduated in pH units and has asensitivity such that discrimination of at least 0.05 pH unit or at least 0.003 V maybe achieved.仪器：测量仪器是一个电压计，其输入电阻至少是所用电极的100 倍。通常标有pH 单位刻度，其灵敏度至少 0.05pH 或 0.003V 。1Method. Unless ot
6、herwiseprescribed in the monograph, all measurements aremade at thesame temperature (20-25 C).方法：除非在各论中另有规定，所有测定均在相同温度(2025 C)下完成。Table shows the variation of pH with respect to temperature of a number of referencebuffer solutions used for calibration.表For the temperature correction,when necessary，f
7、ollow the manufacturers instructions.The apparatus is calibrated with the buffer solution of potassium hydrogen phthalate(primary standard) and 1 other buffer solution of different pH (preferably one shownin Table如必要， 按照制造商的说明进行温度校正。仪器校准用邻苯二甲酸氢钾缓冲液( 基准物质 ) 和另一个不同 pH 值的缓冲液 ( 最好在表The pH of a third buf
8、fersolutionof intermediatepH read offon the scalemust not differby more than 0.05 pH unit from the value corresponding to this solution.pH 值为上述两个缓冲液之间的第三个缓冲液pH 读数不得超过相应pH 值的 0.05个单位。Immerse the electrodes in the solution to be examined and take the reading in the sameconditions as for the buffer sol
9、utions.将电极浸入待测溶液中，在与缓冲液校准相同的条件下，读取待测溶液的读数。When the apparatus is in frequent use, checks must be carried out regularly.如果仪器经常使用，必须定期进行校验。Immerse the electrodes in the solution to be examined and take the reading in the same conditions as for the buffer solutions.将电极浸入待测溶液中，在与缓冲液校准相同的条件下，读取待测溶液的读数。Whe
10、n the apparatus is in frequent use, checks must be carried out regularly.如果仪器经常使用，必须定期进行校验。PREPARATION OF REFERENCE BUFFER SOLUTIONS对照缓冲溶液的配制Potassium tetraoxalate 0.05 M.Dissolve 12.61 g of C4H3KO8,2H2O in carbon dioxide-free water R and dilute to 1000.0 mL with the same solvent.0.05mol/L四草酸钾溶液：取 C
11、4H3KO8,2H2O 12.61g ，用去二氧化碳的水溶解并稀释至1000.0mL 。Potassium hydrogen tartrate, saturated at 25 C.Shake an excess of C4H5KO6vigorouslywithcarbon dioxide-freewaterR at 25 C. Filteror decant. Prepare immediately before use.25 C饱和的酒石酸氢钾溶液：在 25 C 下用去二氧化碳的水溶解过量的酒石酸氢钾，剧烈震摇， 之后过滤或轻轻倒出。临用新制。Potassium dihydrogen ci
12、trate 0.05 M.Dissolve11.41g ofC6H7KO7in carbondioxide-freewaterR and diluteto 1000.0mL withthe same solvent. Prepare immediately before use.20.05mol/L柠檬酸二氢钾溶液：取柠檬酸二氢钾 11.41g ，用去二氧化碳的水溶解并稀释至1000.0mL 。临用新制。Potassium hydrogen phthalate 0.05 M.Dissolve 10.13 g of C8H5KO4, previously dried for 1 h at 110
13、 2 C, in carbondioxide-free water R and dilute to 1000.0 mL with the same solvent.0.05mol/L邻苯二甲酸氢钾溶液：取事先在110 2 C 干燥 1h 的邻苯二甲酸氢钾 10.13g，用去二氧化碳的水溶解并稀释至1000.0mL 。Potassium dihydrogen phosphate 0.025M + disodium hydrogen phosphate 0.025M.Dissolve 3.39 g of KH2PO4 and 3.53 g of Na2HPO4, both previously d
14、ried for 2h at 1202 C,in carbon dioxide-freewater R and diluteto 1000.0 mL with the same solvent.0.025mol/L磷酸二氢钾 + 0.025mol/L磷酸氢二钠溶液：取事先在120 2 C 干燥 2 h 的磷酸二氢钾 3.39g 和磷酸氢二钠 3.53g ，用去二氧化碳水溶解并稀释至 1000.0mL 。Potassium dihydrogen phosphate 0.0087M+disodium hydrogen phosphate 0.0303M. Dissolve1.18 g of KH2PO4 and 4.30 g of Na2HPO4, both previously dried for 2 h at 120 2 C, in carbon dioxide-free water R and dilute to 1000.0 mL with the s
