碘量法测定铜铅合金中铜的方法改进

采用传统碘量法测定铜铅合金中铜时,由于铜铅合金中锑、锡等元素的干扰,导致测定结果不准确。为了准确测定出铜铅合金中的铜含量,实验对上述方法进行了改进:采用酒石酸-硝酸溶解样品,避免产生氯化铅、溴化铅等沉淀,同时抑制了锑和锡的水解;并在高氯酸-硫酸体系下加入5 mL氢溴酸去除样品中的锑、锡等干扰元素;加入3 mL冰乙酸,控制溶液的pH值为3～4,用氟化氢铵掩蔽铁,加入碘化钾与铜(Ⅱ)作用,析出的碘以淀粉为指示剂,用硫代硫酸钠标准滴定溶液滴定,接近化学计量点时加入7 mL硫氰酸钾溶液使碘化亚铜沉淀表面吸附的碘释放;建立了碘量法测定铜铅合金中铜的方法。结果表明,使用改进后的方法能消除共存元素对测定结果的影响。按照实验方法测定铜铅合金中铜,结果的相对标准偏差(RSD,n=11)为0.18%~0.25%,加标回收率为98.85%～100.10%。

Method improvement for the determination of copper in copper-lead alloy by iodometry

Cu-Pb alloy contains antimony, tin and other elements, which have interference with the determination of copper by iodometry. In order to determine the copper content in Cu-Pb alloy accurately, the iodometry was improved. The sample was dissolved with tartaric acid-nitric acid. The formation of lead chloride and lead bromide precipitates was avoided. Meanwhile, the hydrolysis of antimony and tin was inhibited. The interference elements such as antimony and tin in sample were removed by adding 5 mL of hydrobromic acid in perchloric acid-sulfuric acid system. 3 mL of glacial acetic acid was added to control the pH of solution at 3-4. Ammonium hydrogen fluoride was added to mask iron. Potassium iodide was added to react with copper(Ⅱ), and the iodine precipitated was titrated with sodium thiosulfate standard titration solution using starch as the indicator. Near the stoichiometric point, 7 mL of potassium thiocyanate solution was added to release the iodine which was adsorbed on the surface of cuprous iodide precipitate. The determination method of copper content in Cu-Pb alloy by iodometry was established. The results showed that the improved method could eliminate the influence of coexisting elements on the determination results. The content of copper in Cu-Pb alloy was determined according to the experimental method. The relative standard deviations (RSD, n=11) were between 0.18% and 0.25%. The recoveries were between 98.85% and 100.10%.