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九、镁的测定镁离子与乙二胺四乙酸二钠形成相当弱的络合物,其 pK 值为8.7。由于此络合物的稳定性较差,只能在 pH10的氨水-氯化铵缓冲溶液中进行络合滴定,最常用的指示剂为铬黑 T。在铝合金中测定镁时,通常用氢氧化钠溶解试样。由于铝在氢氧化钠中溶解而镁则生成氢氧化镁沉淀,因此用氢氧化钠溶解试样可使镁与大量铝基本分离。合金中其他合金元素如铜、铁、锰、镍、钛、钙及部分锌等则和镁一起留在沉淀中。在最后进行镁的络合滴定前,还需用分离法或掩蔽法消除这些共存元素的
Nine, the determination of magnesium Magnesium ion and ethylenediaminetetraacetic acid to form a relatively weak complex, the pK value of 8.7. Due to the poor stability of this complex, the complexation titration can only be carried out in a pH 10 aqueous ammonia-ammonium chloride buffer. The most commonly used indicator is chrome black T. When measuring magnesium in aluminum alloys, the sample is usually dissolved with sodium hydroxide. Since aluminum dissolves in sodium hydroxide while magnesium forms magnesium hydroxide precipitates, dissolving the sample with sodium hydroxide substantially separates the magnesium from the bulk of the aluminum. Other alloying elements in the alloy such as copper, iron, manganese, nickel, titanium, calcium and some zinc and magnesium stay together in the precipitation. In the final complexation of magnesium before titration, the need to use separation or masking method to eliminate these co-existing elements