Preparation of Pentaamminenitrocobalt III Chloride

Dissolve 1.5 g of [Co(NH3)sCl]Cl2 in 20 cm of 2 M NH3 solution. Heat in a water bath until the salt dissolves. Cool and acidify to pH4 with 4M HCl. Add 2g NaNOj and heat gently until the red precipitate first formed has dissolved. (The precipitate may only appear transiently). Cool and add carefully 20 cm cone. HCl. Cool in ice and filter off the yellow brown crystals and wash with alcohol. Dry by continued suction while pressing between filter paper. Record your yield and calculate the % yield. 

The percentage of cobalt in either isomer or in the previously prepared mixed ligand complexes can be determined as before. 

Weigh out accurately about 0.5 g of any of your preparations in a conical flask. Add 20 cm of dil. NaOH and heat on a sand bath in the fume cupboard to distil off the NH3 liberated. A suspension of black C02O3 remains in the flask. Cool under the tap and filter through GF/C filter and wash well with H2O. Transfer the filter quantitatively to a clean conical flask, add 1.5 g Kl and acidify freely with dil. HCl. Cover with a watch glass and allow to stand until all the black particles have dissolved. Titrate the liberated I2 with standardised 0.1 M Na2S203 solution until the colour fades to straw yellow. Dilute with H2O to 200 cm and add 2 cm freshly prepared starch solution. Continue the titration carefully until the dark blue starch/l2 adsorption complex disappears for 1 minute. At the end-point the pale pink colour of Co(Il) remains in solution. Repeat and calculate from each result the % Co in your preparation and hence its % purity. 

When cobalt is simultaneously coordinated to three ammonia ligands and three nitro groups, a neutral complex is formed which would not give an electrically conducting solution and is likely to be more soluble in organic solvents than the other complexes prepared earlier. Such a complex can be prepared from chemicals similar to the ones used in the other mixed ligand complexes but under different conditions. 

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