![]() The filter paper can be cut into small strips and stored in a desiccator with dry silica gel.Soak filter paper in this solution, drain and dry in an oven (set at no more that 100 ☌), so that it is a definite blue colour.Dissolve 5 g of hydrated cobalt(II) chloride in 100 cm 3 of water (solution is TOXIC).The indicator papers should be handled as little as possible and hands washed after use. Cobalt chloride (TOXIC, DANGEROUS FOR THE ENVIRONMENT, may cause SENSITISATION) – see CLEAPSS Hazcard HC025 and CLEAPSS Recipe Book RB030.Whereas the anhydrous dichloride is blue, the hydrate is red. These halides exist in anhydrous and hydrated forms. Read our standard health and safety guidance. Cobalt (II) chloride hexahydrate Four dihalides of cobalt (II) are known: cobalt (II) fluoride (CoF 2, pink), cobalt (II) chloride (CoCl 2, blue), cobalt (II) bromide (CoBr 2, green), cobalt (II) iodide (CoI 2, blue-black).Hexahydrate cobalt(II) chloride CoCl 2♶H 2O (TOXIC, DANGEROUS FOR THE ENVIRONMENT, SENSITISER ), 5 g.The hexahydrate is deep purple in color, whereas the anhydrous form is pale blue. Cobalt chloride paper is useful because the hydration/dehydration reaction occurs readily making the paper an indicator for water. It is usually supplied as the hexahydrate CoCl 2♶H 2O. You can use the papers to test for the presence of water, where the colour changes from blue to pink.Ĭobalt(II) chloride is an inorganic compound of cobalt and chlorine, with the formula CoCl 2. ![]() This resource provides instructions for preparing your own cobalt chloride indicator papers. RSC Yusuf Hamied Inspirational Science Programme.Introductory maths for higher education.The physics of restoration and conservation.Place 5 mL of the respective sample solutions into test tubes. ![]() Measurement of the Color-Change Temperature. Because the color tone of the reference solution changes depending on temperature, a fine adjustment of the color by adding several drops of 6 M HCl may be required when the ambient temperature is lower than 20 ✬. In addition, a reference color solution of 0 = 0.1 M and 0 = 5.4 M, which is light violet, is prepared in the same manner. All the sample solutions prepared are pink-colored indicating a slight gradient in color tone, Figure 2(a). Table 1 lists the conditions for preparing the series of sample solutions using 0.1 M CoCl 2 and 6 M HCl, where the mixed solutions of the required volumes are diluted to 100 mL with water in a volumetric flask. After repeated trial and error to observe the color change clearly at a temperature ranging from 30 to 60 ✬, conditions for the hydrochloric acid solutions of 0 = 0.1 M and 0 = 4.5~5.2 M were selected. A series of aqueous solutions of CoCl 2 -HCl with varying 0 and a constant 0 are required. Figure 2 illustrates typical experimental steps. It is a skin, eye, and respiratory irritant and repeated exposure can lead to poisoning. #) is harmful by inhalation and ingestion. ![]() ![]() The present experiment is useful to deepen student understanding of the temperature effect on the equilibrium shift and to introduce chemical thermodynamics at equilibrium. Using the measured data for color- change temperatures and the calculated equilibrium constants at those temperatures, the standard enthalpy change DHº is evaluated by a van’t Hoff plot. Through a simple experiment of measuring the color change temperatures for a series of cobalt(II) chloride solutions with different concentrations of hydrochloric acid, the temperature dependence of the equilibrium constant is estimated. It was found that the equilibrium constant at the temperature of the color change between the pink octahedral complex and deep-blue tetrahedral complex can be expressed approximately as a function of the concentration of hydrochloric acid. For the equilibrium system of cobalt(II) chloride in hydrochloric acid, a simple student experiment to discuss quantitatively the equilibrium shift depending on temperature was examined. ![]()
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