Synthesis of Chloropentaamminecobalt (iii) Chloride

Introduction

Cobalt was discovered by Georg Brandt in 1735 interestingly the name Cobalt originates form the German word “Kobald” which means goblin or evil spirit. The original use of cobalt was value to early civilisation of Egypt for colouring glass blue. Alfred Werner was a pioneer in coordination Chemistry determined the isomer cobalt (III) hexamine chloride.

Experimental

Ammonium chloride (1.306g) was dissolved in concentrate ammonia solution (10.5cm3) forming a colourless solution. Colablt(II)chloride hexahydrate (2.494g) was added in small portions with t stirring producing a muddy liquid with a dark precipitate. 27% Hydrogen peroxide (2.25cm3) was added using a dropping pipette with constant stirring. A small amount of heat and effervescence (bubbling) was visible. Once the reaction has stopped and a dark red solution was formed to which Concentrate Hydrochloric acid (10cm3) was added very slowly with constant stirring. A large amount of heat was released and a white gas was given off forming a dark pink solution. This solution was heated for 18mins before being cooled in ice forming dark pink precipitate. The solution was filtered and washed with dilute hydrochloric acid (5cm3) ethanol (5cm3) and acetone (5.5cm3). Once dry the crystals (1.447g ??%) were transferred to an open sample vial and dried in a desiccator for a week.

A portion of this product (???g) was dissolved in Dilute ammonia (10cm3), water (40cm3) was added. The solution was heated (15 mins) forming a clear red solution. Concentrate Hydrochloric acid ( 10cm3) was added followed by Ammonium chloride (1.00g) forming a orange solution. The resulting solution was heated for a further 25mins. COLOURS ??. Solution was cooled in ice and the product filtered off and washed with hydrochloric acid (5cm3) ethanol (5cm3) and acetone (5.5cm3). Forming 0.??g ??%)

Ammonium chloride(5.02g), Cobalt(II) chloride hexahydrate(1.396g) and Sodium Iodide (0.192g) were dissolved Water (10cm3) producing a deep pink purple colour. Powdered iodine (0.718g) was added forming a ?????? colour. Concentrate Ammonia (5.2cm3) was added with stirring forming a light muddy brown grey then turned greyer on after a further 30mins of stirring. The resulting solution was left to stand for 1 min and then the liquid was decanted off, water (20cm3) was added and decanted off and then Ethanol (20cm3). The resulting precipitate was dried under suction with further Ethanol washings (15cm3) producing (1.404g ??%)

Ammonium Chloride (1.0g) was dissolved in Boling water (3.5cm3). Cobalt(II) chloride hexahydrate (1.548g) was added producing a deep royal blue solution. Charcoal (?0.75g) was added turning the solution grey black. The solution was cooled in an ice bath to 5oC and Concentrate Ammonia (4.5cm3) was added in small portions over 3 mins. Hydrogen peroxide (23% vol) (4cm3) was added in portions over 5 mins. The solution was then heated to 60oC for 1 min. The solution was re cooled to 3oC in an ice bath. The black oily precipitate was filtered under suction before being added to Boiling water (12cm3). Concentrate Hydrochloric acid (0.5cm3) was added and then the solution filtered. Concentrate Hydrochloric acid (2cm3) was added to the filtrate (liquid) and the solution cooled in ice. The resulting orange precipitate was filtered and washed with acetone (10cm3) producing (0.444g ??%)

Results and discussion

Equations

ΔM= Molar Conductivity (S m2 mol L-1)

= Measured conductivity (units S m-1)

c = Concentration (units mol m3)

A mol L-1 = A x100 mol m3

A µS cm-1= (A /10000) S m-1

n=M/Mr

n= Moles

M= Mass (units grams)

Mr = Molecular weight

n= C x V

n = moles

C = Concentration (units mol L-1)

V= Volume (L)

100cm3= 0.1L

Preparation of Chloropentaamminecobalt (III) chloride

Ammonium chloride +Ammonia+ Cobalt (II) chloride hexahydrate à Chloropentaamminecobalt (III) chloride

NH4Cl + CoCl2.6H2O + NH3 à [Co(NH3)5Cl]Cl2

Calculation of Concentration of Chloropentaamminecobalt(III) chloride in 100cm3 volumetric flask

n=M/Mr

M= 0.1100g

Mr Chloropentaaminecobalt(III) chloride = 267.4762

n = 0.1100/267.4762

n= 4.1125431×10-4

n=CV

4.1125431 x10-4= C x 0.1

C= 4.1125 x10-3mol L-1 à 0.41125 mol m3

Conductivity = 1286µS à 0.1286 S m-1

S m2 mol L-1

Preparation of iodopentaaminecobalt(III) chloride

Iodine + Cobalt(II) Chloride hexahydrate + Ammonia+ Ammonium chloride àIodopenaaminecobalt(III) chloride

I2 + CoCl2.6H2O + NH4Cl + NH3 à [Co(NH3)5I]Cl2

n=M/Mr

M= 0.0934g

Mr iodopentaaminecobalt(III) chloride = 341.90

n = 0.0934/341.90

n= 2.73179 x10-4

n=CV

2.73179×10-4= C x 0.1

C= 2.7317929 x10-3mol L-1 à 0.27317929 mol m3

Conductivity = 1137µS à 0.1137 S m-1

S m2 mol L-1

Preparation of hexaaminecobalt(III) chloride

Ammonium chloride + Cobalt(II) chloride hexahydrate +Ammoniaà Hexaamminecobalt(III) chloride.

NH4Cl + CoCl2.6H2O+ NH3 à Co(NH3)6]Cl3

n=M/Mr

M= 0.1010g

Mr Hexaamminecobalt(III) chloride =267.4762

n = 0.1010/267.4762

n= 3.776036896 x10-4

n=CV

3.776036896 x10-4= C x 0.1

C= 3.776036896 x10-3mol L-1 à 0.3776036896 mol m3

Conductivity = 1720µS à 0.1720 S m-1

S m2 mol L-1