Analysis of a Co-ordination Compound
Spectrophotometric analysis of cobalt.
This section analyses the results of the experiment. The analysis of cobalt is conveniently done by spectrophotometric analysis
Analysis of the visible spectrum of cobalt (II) ion
i. Prepare solutions of different concentrations by diluting the stock solution with distilled water using a 10 ml pipette.
ii. Using the wavelength of minimum transmittance found from the visible spectrum of cobalt (II) ion stock solution, measure and record the percentage transmittance and absorbance of each diluted solution.
Analysis of unknown coordination compound of cobalt
i. Weigh 2.5g of the unknown compound into a dry 50ml beaker.
ii. Cover the beaker with a watch glass and put it on a hot plate at about 3500C and heat until the sample turns into a liquid, foams and turns blue.
iii. Remove the beaker and its contents from the hot plate; allow it to cool to room temperature.
iv. Add 10ml of distilled water and 1 ml of concentrated sulphuric acid to the sample, boil the mixture gently to dissolve the solid. Cool it then to room temperature.
v. Transfer the contents of the beaker carefully to 100ml volumetric flask, filling it to the mark with distilled water. Mix it thoroughly.
vi. Measure and record the percentage transmittance and absorbance of the unknown solution at the same wavelength used for the stock solution.
Percentage cobalt= concentration of Co () (100ml) () ()
Volumetric Analysis of Ammonia Content
Add 50 ml saturated boric acid solution in the 125 ml conical flask; with five drops of the indicator.
Put 1 g of the compound into a beaker and transfer in flask using.
Add Distilled water to give a final volume of about 50 ml.
Add a few boiling chips and several pieces of granulated zinc.
Add 40 ml 6 M NaOH with 50ml distilled water into the flask to recover ammonia.
Gravimetric analysis of chloride
- Weigh three sample of the unknown compound of 0.45 to 0.55g, placing them in a 250 ml beaker.
- Weigh a second watch glass and carefully transfer the dry crystals onto it. Record the masses and transfer the compound to a weighing bottle. Add about 150 ml of distilled water to the compound and stir to dissolve. Add 1ml of 6M nitric acid to acidify the solution.
- Slowly add 30 ml of 0.25M silver nitrate, while continuously stirring at room temperature to precipitate the chloride. This is carried in a subdued light to avoid decomposition of silver chloride.
- Heat the suspension while stirring until it starts to boil. Stir further for a minute for coagulation of the precipitate. Remove the beaker and contents from heat, cover with a watch glass and leave to stay overnight.
- Collect the silver chloride in a cleaned filter crucible making sure that no precipitate is lost.
- Wash the residue with 0.01M nitric acid added in small portions.
- Heat the crucible and contents at 1500C for about an hour, cool it for 30 minutes, weigh it record the mass.
Interpretation of results
The percentage composition of chlode in the unknown compound is