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

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

3. 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) I-(aq)  2 Co2+(aq) I2(aq)
The liberated Iodine is then titrated against stand sodium thiosulfate solution

4. New techniques:
Recrystallisation
Reflux
Distillation

5. 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)

6. 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)

7. 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

8. 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

9. 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

10. 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

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

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