METALS: COBALT Cobalt, usually found in the Earth's crust as a sulfide (e.g., in the ore cobaltite), is the second rarest (0.003%) of the four elements that can be magnetized; the other three are iron (5.6%), nickel (0.008%), and gadolinium (0.0005%). This relative rarity means that cobalt is not used for structural purposes but for the formation of specialized alloys (e.g., Alnico, which is used to manufacture permanent magnets). This transition metal, which has a high melting point (1495°C) and a high density (8.89 g cm-³), forms compounds in several oxidation states [e.g., (blue) cobalt(II) chloride and (brown) cobalt(III) chloride]. [.. K > Ca > Na > Mg > Al > Zn > Fe > Co > Sn > (H) > Cu > Hg > Ag ..]
1. The extraction of cobalt from its ores is complex, but the final process usually involves chemical reduction of cobalt(II) dicobalt(III) oxide (Co3O4). Construct the symbol equation for the reduction of this tetroxide with each of these reducing agents used in industry: Aluminium _____________________________________________________________ Carbon ________________________________________________________________ Dihydrogen ____________________________________________________________  Cobalt can be electrolytically purified, using impure cobalt as the anode, pure cobalt as the cathode, and aqueous cobalt(II) chloride as the electrolyte. Explain why solid cobalt(II) chloride would not be suitable as an electrolyte. ___________________________________________ _______________________________________________________________________ _______________________________________________________________________  2. Vitamin-B12, which is synthesized exclusively by bacteria (e.g., Methanobacteria), has a structure similar to both chlorophyll-a and haemoglobin.
This compound is involved in the bacterial biosynthesis of methane and organometallic compounds of heavy metals (e.g., dimethylmercury).
Vitamin-B12 is also a vital cofactor in the synthesis of mammalian red blood cells; it is acquired from dietary sources and from symbiotic bacteria residing in the alimentary canal. Name the human deficiency disease caused by a lack of this vitamin. _____________________________ 
3. Cobalt(II) chloride is used as an indicator of water; thus, in the presence of this compound, blue 'cobalt(II) chloride paper' turns pink:
State and explain, using Le Chatelier's Principle, the effect of an increase in temperature on this reaction. _____________________________ _______________________________________________________________________ _______________________________________________________________________  4. Anhydrous cobalt(II) chloride is an effective catalyst for the synthesis of alkanes (in non-aqueous solvents); a typical scheme is:
(a) Construct a similar scheme for the synthesis of pentane (C5H12). _______________________________________________________________________ _______________________________________________________________________  (b) Complete and label the energy level diagram for this synthesis of pentane. Energy ___ ___ ___________________ _ _ _ _ _ _ _ _ _ _ _ _ ___________________ _______________ _______________ ___________________________________________ Path of reaction  (c) Compounds with the same molecular formula but different structural formulae are known as isomers. Complete these structural formulae to show the three alkane isomers which have a molecular formula of C5H12. C C C C C C C C C C C C C C C pentane 2-methylbutane 2,2-dimethylpropane  (d) Suggest one physical method which could be used to distinguish between these three isomers. __________________________________________  5. One radioactive isotope of cobalt, Co-60, has been used in the treatment of cancer; it has a half-life of 5.3 years; and spontaneously emits both b-particles and g-rays (i.e., high speed electrons and high frequency photons, respectively). Determine how many protons, neutrons, and electrons there are in each of the following. Co-59 _________________________________________________________________ Co-60 _________________________________________________________________ Co(III)-60 ____________________________________________________________ 
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