8303128-046-Transition-Metals-2 - Chem Factsheet January...

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Transition Metals 2 - Compounds and Reactions C hem F actsheet January 2003 Number 46 1 To succeed in this topic you need to: Understand the principle of oxidation numbers. Understand types of bonding and molecular shapes. Understand the basics of Transition Metals (covered in Factsheet 38) After working through this Factsheet you will: Have more experience of transition metal compounds; Recall the reactions of transition metal ions with hydroxides and ammonia; Recall the oxidation states of vanadium, and how they can be interconverted. The following simple test tube reactions illustrate the behaviour of transition metal ions. Addition of aqueous alkali to transition metal ions Practical 1 – Addition of sodium hydroxide solution Dilute sodium hydroxide solution is added dropwise to aqueous transition metal ions. Initially a precipitate is looked for, then the sodium hydroxide is added to excess to find out if the precipitate will eventually re-dissolve. Ion Addition of NaOH (aq) Excess NaOH (aq) Cr 3+ Green ppt Green solution Mn 2+ Buff ppt, darkens in air Precipitate does not dissolve Fe 2+ Pale green ppt, browns on surface Precipitate does not dissolve Fe 3+ Red brown ppt Precipitate does not dissolve Co 2+ Blue ppt, turns brown in air Precipitate does not dissolve Ni 2+ Pale green Precipitate does not dissolve Cu 2+ Pale blue ppt Precipitate does not dissolve Zn 2+ White ppt Colourless solution The equations for these reactions are similar; each of the transition metal ions should be written as the hexa-aqua ion, except for zinc which forms a tetra-aqua ion. In each case the precipitates formed are the simple hydroxide compounds. For example: [Mn(H 2 O) 6 ] 2+ (aq) + 2OH (aq) Mn(OH) 2 (s) + 6H 2 O (l) [Fe(H 2 O) 6 ] 3+ (aq) + 3OH (aq) Fe(OH) 3 (s) + 6H 2 O (l) and for zinc, [Zn(H 2 O) 4 ] 2+ (aq) + 2OH (aq) Zn(OH)
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This note was uploaded on 03/08/2011 for the course CHEM 101 taught by Professor Hard during the Spring '11 term at UT Arlington.

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8303128-046-Transition-Metals-2 - Chem Factsheet January...

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