Preparation and analysis of Cobalt complexes The aim of this investigation is to prepare two cobalt complexes and analyse them

Preparation of Cobalt complexes Complex A - [Co(NH3)6]Cl3 Complex B - [Co(NH3)5Cl]Cl2

Analysis - Cobalt Determination Using Alkaline Hydrolysis followed by Redox titration Theory : the alkaline hydrolysis leaves a residue of Cobalt (III) oxide Co2O3. These Cobalt ions are reacted with Iodide ions to produce Iodine 2Co3+(aq) + 2I-(aq)  2 Co2+(aq) + I2(aq) The liberated Iodine is then titrated against stand sodium thiosulfate solution

New techniques: Recrystallisation Reflux Distillation

Analysis – Ammonia Determination Alkaline hydrolysis: of Complex A and B NH3(g)liberated during hydrolysis reacts with a standard solution of excess HCl(aq) The remaining HCl(aq) is titrated with sodium hydroxide using a back titration. NaOH(aq) + HCl(aq)  NaCl(aq) + H2O(l)

Analysis – Chloride determination Theory – Chloride concentration is determined by Mohrs titration. This is an example of a precipitation titration as the chloride content is analysed by a titration using standard silver nitrate solution –to form a precipitate of AgCl Ag+(aq) + Cl-(aq)  AgCl(s) When all the chloride ions have reacted you get a red precipitate of the indicator chromate ions 2Ag+(aq) + CrO42-  Ag2CrO4(s)

Analysis – Total chloride and Free chloride Theory – In analysing the Chloride it is possible to analyse the total chloride which is present in the complex and compare it to the free chloride value Free chloride ions are not ligands directly bonded to the central Cobalt ion. Chloride ions which are ligands can be removed by passing them over an amberlite resin. Using a Mohrs titration if chloride ligands are present in the complex then the free chloride value will be lower than the total chloride value

Cobalt – Results Calculate the percentage yield for each complex Calculate the number of moles of Cobalt in your sample of complex and the therefore the mass of Cobalt in the complex Calculate the number of moles of Ammonia in the complex and the mass of the ammonia The ratio of number of moles of cobalt to ammonia will help identify the complex

Cobalt Results Calculate the number of moles of total chloride in the complex and the mass of chloride Calculate the number of moles of chloride after chloride ligands removed (free chloride) and the mass of this chloride Check ratio of free chloride to total chloride

Cobalt Complex – Planning Read the articles provided to get some background about aspirin and understand the synthesis of it Read the practical methods and familiarise yourself with the techniques Have a think about how complex you want your project to be

Cobalt – Risk Assessment The following chemicals need to be carefully risk assessed: Hydrogen peroxide Cobalt chloride Ammonia Ammonium Chloride Potassium chromate Silver nitrate ethanol

Calibration Curve Make up solutions of known concentration and measure absorbance Plot calibration curve Then measure absorbance of your own sample and determine concentration