用 TRIS 对盐酸进行标准化
AN-T-102
2020-05
zh
Correct titer improves the accuracy of results
滴定剂通常即买即用。但是，有需要定期使用一级标准来确定滴定溶液的准确浓度。为了纠正上述变化，需要使用所谓的 “滴定系数”。使用瑞士万通品牌的自动电位滴定仪可以方便快捷地评估滴定度。瑞士万通的电位滴定仪或软件分别采用预定义的计算公式，并自动存储滴定系数，使标准化工作变得简单。
Titrants are normally bought ready to use. However, the certified value is only valid at a defined temperature because the titrant density varies with temperature. With time and especially after opening the bottle of your titrant, the properties thereof will change because of evaporation of water and uptake of carbon dioxide. Due to these facts, it is necessary to determine the accurate concentration of your titrant solution on a regular basis using a primary standard. To correct the mentioned variation, a socalled «titer factor» is applied.
In case of hydrochloric acid as titrant, the primary standard to use is TRIS (Tris(hydroxymethyl)aminomethan). TRIS is inert, does not sublimate, and reacts with hydrochloric acid according to a defined chemical reaction.
The titer can be easily and quickly assessed by using the Metrohm brand of autotitrators. Predefined calculation formulas implemented in Metrohm titrators or software, respectively, as well as the automatic storage of the titer factor, makes standardization a simple task.
High purity TRIS is used for the standardization of hydrochloric acid. TRIS is dried in a drying oven for several hours and allowed to cool down to ambient temperature in a desiccator.
An appropriate amount of TRIS standard is added accurately to a beaker and dissolved with deionized water. The solution is titrated against hydrochloric acid until after the equivalence point is reached.
The sample size must be chosen according to the buret volume (equivalence point between 10–90% of buret volume).
If a small cylinder unit (2 or 5 mL cylinder unit) is used for titration, it is recommended to make a stock solution and use an aliquot thereof for titration. This increases the accuracy for these burets.
A six-fold determination exhibited a mean titer value of 1.0069 with an absolute standard deviation of 0.0037 and a relative standard deviation of 0.37%.
The determination of the titer of hydrochloric acid is performed both quickly and reproducibly.
Easy, fast, and precise titer determination using Metrohm autotitrators results in reliable titration analyses. Predefined calculation formulas implemented in these titrators or software, respectively, as well as the automatic storage of the titer factor makes standardization a simple task.
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