Le Chatelier’s Principle

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Title : Application of Le Chatelier’s Principle to some solution reactions. Aim : To investigates the application of Le Chatelier’s Principle to some solution reactions. Apparatus : 5 mL measuring cylinder, test tubes, 50 mL beaker, Bunsen burner, dropper. Materials : 0.1 mol L⁻¹ potassium chromate(VI) solution [K₂CrO₄], 0.1 mol L⁻¹ potassium dichromate(VI) solution [K₂Cr₂O7 ], (0.2 mol L⁻¹ and 1.0 mol L⁻¹) hydrochloric acid solution [HCL], 0.2 mol L⁻¹ sodium hydroxide solution (NaOH), cobalt (II) chloride hexahydrate peasized [CoCl₂.6H₂O], distilled water. Introduction : Part A : Chromates and dichromates are salts of chromic and dichromic acid. Salts have an intense yellow or orange color, respectively. When solid potassium dichromate (K2Cr2O7) is dissolved in water the resulting solution is orange. The dichromate ion in aqueous solution is in equilibrium with the chromate ion, and this can be shown with the following equation: This is a dynamic equilibrium and as such is sensitive to the acidity or basicity of the solution. Shifting the equilibrium with pH changes is a classic example of Le Chatelier’s principle at work. Le Chatelier's principle states that if a chemical dynamic equilibrium is disturbed by changing the conditions (concentration, temperature, volume or pressure), the position of equilibrium moves to counteract the imposed change. So if more reactant is added, the equilibrium shifts to the right in order to consume that extra reactant, which results in more product; also if the product is removed from the system, the equilibrium shifts to the right completely increasing the yield. Yellow chromate and orange dichromate are in equilibrium with each other in aqueous solution. The more acidic the solution, the more the equilibrium is shifted to the left towards the dichromate ion. As hydrochloric acid is added to the chromate solution, the yellow
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