Preparation of sodium hexanitrocobaltate free essay sample

Sodium hexanitrocobaltate (III) is a coordination complex which has the formula Na3[Co(NO2)6]. This compound is yellow in colour. It consists of a central Co3+ ion surrounded by six nitro ligands [1]. This compound is used as a qualitative test for potassium and ammonium ions (so long as certain other cations are not present) [1]. Potassium and ammonium are insoluble in water, while sodium is [1]. Hence, the potassium and ammonium salts are precipitated as a yellow solid. AIM To prepare sodium hexanitrocobaltate (III) from pure potassium-free sodium nitrite, cobalt nitrate hexahydrate, 50% acetic acid and 95% ethanol. In this practical, the nitrite ions acts as an oxidant and a ligand [2]. Co2+ (aq) is more stable than Co3+ (aq), however when cobalt attaches to nitrogen containing ligands, Co3+ becomes the more stable ion [2]. Initially, the hexanitrocbaltate reduces the excess nitrite. The reaction produces nitrogen oxide gas, which reacts with air to form nitrogen dioxide [2]. These gases are removed when the solution is introduced to a steady stream of air [3]. We will write a custom essay sample on Preparation of sodium hexanitrocobaltate or any similar topic specifically for you Do Not WasteYour Time HIRE WRITER Only 13.90 / page Reaction Equation: Co(NO2)3 + 5NaNO3 + 2NO3 Na3[Co(NO2)6] + 2NaNO3 + NO + H2O STRUCTURE MATERIAL 12 grams pure potassium-free sodium nitrite  12 ml cold water 4 grams cobalt nitrate hexahydrate 4 ml 50% acetic acid ethanol ice glass rod dropper hotplate beakers measuring cylinder weighing boat test tube filter paper funnel filter flask aeration tube scale vacuum pump METHOD 12. 01 grams of pure potassium-free sodium nitrite was weighed and added to 12 ml of cold water in a 100 ml beaker. This mixture was then heated on the hotplate until the solid was completely dissolved. The resulting solution was cooled to 50 0C. 4. 07 grams of colbalt nitrate hexahydrate was weighed and dissolved in the cooled solution. Thereafter, 4 ml of 50% acetic acid was added dropwise to the solution while being stirred continuously. The solution obtained was transferred into a test tube, placed into a filter flask and attached to an aeration tube. The vacuum pump was opened slowly to allow a steady stream of air to flow through the solution. This was done for approximately 20 minutes. After 20 minutes, the solution was placed in an ice bath, where 20 ml of 95% ethanol was added slowly while stirring. The mixture was left to stand for 20 minutes in the ice bath to crystallize. The product was filtered and washed three times with 10 ml of ethanol. The dried product was weighed to determine the percentage yield obtained. RESULTS Weight (g) NaNO3 (pure potassium-free sodium nitrite)12. 01 Co(NO2)3 (cobalt nitrate hexahydrate)4. 07 Na3[Co(NO2)6] (sodium hexanitrocobaltate (III))9. 11 Table showing data obtained from the experiment Calculations: Molar Mass (g/mol) NaNO3 (pure potassium-free sodium nitrite)196. 96 Co(NO2)3 (cobalt nitrate hexahydrate)85. 00 Na3[Co(NO2)6] (sodium hexanitrocobaltate (III))403. 96 Table showing the molar masses of the different compounds Number of moles of Co(NO2)3 = mass/molar mass = 4. 07/196. 96 = 0. 0207 mols Stoichiometric ratio of Co(NO2)3: Na3[Co(NO2)6] = 1 : 1 ? Number of moles of Na3[Co(NO2)6] = 0. 0207 mols Mass of product = Molar mass ? number of moles = 403. 96 ? 0. 0207 = 8. 36 g Percentage yield obtained = (Actual Yield)/(Theoretical Yield)? 100 = 9. 11/8. 36? 100 = 108. 95 % The limiting reactant was determined from the following calculation: Co(NO2)6 and 5NaNO3 0. 0207 mols x mols (number of moles available for reaction) 1 5 (stoichiometry) x = 0. 1035 mols†¦ number of moles of NaNO3 needed for the reaction However, actual number of moles of NaNO3 available for the reaction is 0.  1413 mols. Therefore, NaNO3 will be in excess, while Co(NO2)3 is the limiting reactant. OBSERVATIONS When the cobalt nitrate hexahydrate was dissolved in the solution of pure potassium-free sodium nitrite, the mixture turned reddish brown in colour. As the 50% acetic acid was added to the solution, its colour changed to a yellow and became thicker in consistency. As the solution cooled, a l ayer of brownish solution was observed at the top of the product. The final product of sodium hexanitrocobaltate (III) was seen to be a yellowish powder. DISCUSSION A yield of over 100% was obtained. This result obtained has some errors that can be due to: Not filtering and drying the product sufficiently, leaving the product with excess water. Human error while measuring. Some product could remain in the beaker. Product could have spilled while transferring the product from the beaker to the filter funnel. While removing the filter paper, product could have dropped or could remain in the funnel. CONCLUSION The aim of the experiment was to prepare sodium hexanitrocobaltate (III), which was achieved. A yield of 108. 95% was obtained, which was said to be as a result of errors while conducting the practical.