十二钨钴酸钾的动力学测定

Measurement of Dynamics of K_5CoW_(12)O_(40)

十二钨钴酸钾具有四面体结构,其中金属离子是配合物的中心原子,作为配体的多酸阴离子(W3O10)在四面体顶角,它们具有Keggin结构。本实验用紫外可见光谱测定法,以287nm为测定波长,测定浓度为8 0×10-4mol/L的K5CoW12O40溶液与浓度分别为4 0×10-3、6 0×10-3、8 0×10-3mol/L、12×10-3mol/L的NaNO2溶液进行氧化还原反应时的吸光度。以不同浓度时的ln(A—A∞)对t作图呈线形关系,确定氧化剂反应级数为一。以不同的kobs对还原剂浓度作图,其图形也呈直线,确定还原剂的反应级数也为一,其反应的速率常数K=0 21×103(min-1)。说明K5CoW12O40的氧化还原反应机理是外界反应机理。此法在杂多酸化学中有着重要的意义。

K_5CoW_(12)O_(40) has a tetrahedral structure. Reaction between K_5CoW_(12)O_(40) and NaNO_2 is an oxidation-reduction type of reaction. Intensity of light-absorbing was measured with wavelength of 287nm by visible and ultra-violet absorption spectrometry. The concentration of NaNO_2 solution is 4.0×10^(-3), 6.0×10^(-3), 8.0×10^(-3) mol/L and 12×10^(-3) mol/L respectively. Different ln(A-A)is linear with time which means the oxidation reaction is first order reaction. The Kobs is linear with concentration of reductive agent. The reduction reaction is first order reaction too. The rate constant K is 0.21×103(min^(-1)). Mechanism of oxidation-reduction is electronic translation of molecular interaction. It is important for study on heteropolyacid.