Abstract image of a woman sitting on books and studying on a laptop

Transition metal complexes unit 1

Download as PPT, PDF
D
dean dundas

This document provides an introduction to transition metal complexes. It discusses the aqueous chemistry of metal ions, including hydrolysis. Hexaaqua ions form when transition metals dissolve in water and are surrounded by six water molecules in an octahedral structure. Hydrolysis occurs when water molecules attack these complexes, removing protons and forming hydroxide ions. This makes the solution acidic. The document also discusses stability constants, which are equilibrium constants for the formation of complex ions from their constituent parts. Higher stability constants indicate more stable complexes.

Science
1 of 54
Downloaded 90 times
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
Most read
41
42
Most read
43
44
45
46
47
48
49
50
51
52
53
Most read
54
AN INTRODUCTION TOAN INTRODUCTION TO TRANSITION METALTRANSITION METAL COMPLEXESCOMPLEXES KNOCKHARDY PUBLISHINGKNOCKHARDY PUBLISHING 20082008 SPECIFICATIONSSPECIFICATIONS
INTRODUCTION This Powerpoint show is one of several produced to help students understand selected topics at AS and A2 level Chemistry. It is based on the requirements of the AQA and OCR specifications but is suitable for other examination boards. Individual students may use the material at home for revision purposes or it may be used for classroom teaching if an interactive white board is available. Accompanying notes on this, and the full range of AS and A2 topics, are available from the KNOCKHARDY SCIENCE WEBSITE at... www.knockhardy.org.uk/sci.htm Navigation is achieved by... either clicking on the grey arrows at the foot of each page or using the left and right arrow keys on the keyboard KNOCKHARDY PUBLISHINGKNOCKHARDY PUBLISHING TRANSITION METALSTRANSITION METALS
CONTENTS • Aqueous metal ions • Acidity of hexaaqua ions - stability constants • Introduction to the reactions of complexes • Reactions of cobalt • Reactions of copper • Reactions chromium • Reactions on manganese • Reactions of iron(II) • Reactions of iron(III) • Reactions of silver and vanadium • Reactions of aluminium TRANSITION METALSTRANSITION METALS
THE AQUEOUS CHEMISTRY OF IONS - HYDROLYSISTHE AQUEOUS CHEMISTRY OF IONS - HYDROLYSIS when salts dissolve in water the ions are stabilised this is because water molecules are polar hydrolysis can occur and the resulting solution can become acidic the acidity of the resulting solution depends on the cation present the greater the charge density of the cation, the more acidic the solution cation charge ionic radius reaction with water / pH of chloride Na 1+ 0.095 nm Mg 2+ 0.065 nm Al 3+ 0.050 nm the greater charge density of the cation... the greater the polarising power and the more acidic the solution
THE AQUEOUS CHEMISTRY OF IONS - HYDROLYSISTHE AQUEOUS CHEMISTRY OF IONS - HYDROLYSIS when salts dissolve in water the ions are stabilised this is because water molecules are polar hydrolysis can occur and the resulting solution can become acidic the acidity of the resulting solution depends on the cation present the greater the charge density of the cation, the more acidic the solution cation charge ionic radius reaction with water / pH of chloride Na 1+ 0.095 nm dissolves 7 Mg 2+ 0.065 nm slight hydrolysis Al 3+ 0.050 nm vigorous hydrolysis the greater charge density of the cation... the greater the polarising power and the more acidic the solution
THE AQUEOUS CHEMISTRY OF IONSTHE AQUEOUS CHEMISTRY OF IONS Theory aqueous metal ions attract water molecules many have six water molecules surrounding them these are known as hexaaqua ions they are octahedral in shape water acts as a Lewis Base – a lone pair donor water forms a co-ordinate bond to the metal ion metal ions accept the lone pair - Lewis Acids
THE AQUEOUS CHEMISTRY OF IONSTHE AQUEOUS CHEMISTRY OF IONS Theory aqueous metal ions attract water molecules many have six water molecules surrounding them these are known as hexaaqua ions they are octahedral in shape water acts as a Lewis Base – a lone pair donor water forms a co-ordinate bond to the metal ion metal ions accept the lone pair - Lewis Acids Acidity as charge density increases, the cation has a greater attraction for water the attraction extends to the shared pair of electrons in water’s O-H bonds the electron pair is pulled towards the O, making the bond more polar this makes the H more acidic (more δ+) it can then be removed by solvent water molecules to form H3O+ (aq).
HYDROLYSIS -HYDROLYSIS - EQUATIONSEQUATIONS M2+ ions [M(H2O)6]2+ (aq) + H2O(l) [M(H2O)5(OH)]+ (aq) + H3O+ (aq) the resulting solution will now be acidic as there are more protons in the water this reaction is known as hydrolysis - the water causes the substance to split up Stronger bases (e.g. CO3 2- , NH3 and OH¯ ) can remove further protons...
HYDROLYSIS -HYDROLYSIS - EQUATIONSEQUATIONS M3+ ions [M(H2O)6]3+ (aq) + H2O(l) [M(H2O)5(OH)]2+ (aq) + H3O+ (aq) the resulting solution will also be acidic as there are more protons in the water this SOLUTION IS MORE ACIDIC due to the greater charge density of 3+ ions Stronger bases (e.g. CO3 2- , NH3 and OH¯ ) can remove further protons...
HYDROLYSIS OF HEXAAQUA IONSHYDROLYSIS OF HEXAAQUA IONS Lewis bases can attack the co-ordinated water molecules. Theoretically, a proton can be removed from each water molecule turning the water from a neutral molecule to a negatively charged hydroxide ion. This affects the overall charge on the complex ion. [M(H2O)6]2+ (aq) [M(OH)(H2O)5]+ (aq) [M(OH)2(H2O)4](s) [M(OH)2(H2O)4](s) [M(OH)3(H2O)3]¯(aq) [M(OH)4(H2O)2]2- (aq) [M(OH)4(H2O)2]2- (aq) [M(OH)5(H2O)]3- (aq) [M(OH)6]4- (aq) When sufficient protons have been removed the complex becomes neutral and precipitation of a hydroxide or carbonate occurs. e.g. M2+ ions [M(H2O)4(OH)2](s) or M(OH)2 M3+ ions [M(H2O)3(OH)3](s) or M(OH)3 OH¯ H+ OH¯ H+ OH¯ H+ OH¯ H+ OH¯ H+ OH¯ H+
HYDROLYSIS OF HEXAAQUA IONSHYDROLYSIS OF HEXAAQUA IONS Lewis bases can attack the co-ordinated water molecules. Theoretically, a proton can be removed from each water molecule turning the water from a neutral molecule to a negatively charged hydroxide ion. This affects the overall charge on the complex ion. [M(H2O)6]2+ (aq) [M(OH)(H2O)5]+ (aq) [M(OH)2(H2O)4](s) [M(OH)2(H2O)4](s) [M(OH)3(H2O)3]¯(aq) [M(OH)4(H2O)2]2- (aq) [M(OH)4(H2O)2]2- (aq) [M(OH)5(H2O)]3- (aq) [M(OH)6]4- (aq) When sufficient protons have been removed the complex becomes neutral and precipitation of a hydroxide or carbonate occurs. e.g. M2+ ions [M(H2O)4(OH)2](s) or M(OH)2 M3+ ions [M(H2O)3(OH)3](s) or M(OH)3 OH¯ H+ OH¯ H+ OH¯ H+ OH¯ H+ OH¯ H+ OH¯ H+
HYDROLYSIS OF HEXAAQUA IONSHYDROLYSIS OF HEXAAQUA IONS Lewis bases can attack the co-ordinated water molecules. Theoretically, a proton can be removed from each water molecule turning the water from a neutral molecule to a negatively charged hydroxide ion. This affects the overall charge on the complex ion. [M(H2O)6]2+ (aq) [M(OH)(H2O)5]+ (aq) [M(OH)2(H2O)4](s) [M(OH)2(H2O)4](s) [M(OH)3(H2O)3]¯(aq) [M(OH)4(H2O)2]2- (aq) [M(OH)4(H2O)2]2- (aq) [M(OH)5(H2O)]3- (aq) [M(OH)6]4- (aq) In some cases, if the base is strong, further protons are removed and the precipitate dissolves as soluble anionic complexes such as [M(OH)6]3- are formed. Very weak bases H2O remove few protons Weak bases NH3, CO3 2- remove protons until precipitation Strong bases OH¯ can remove all the protons OH¯ H+ OH¯ H+ OH¯ H+ OH¯ H+ OH¯ H+ OH¯ H+ Precipitated
HYDROLYSIS OF HEXAAQUA IONSHYDROLYSIS OF HEXAAQUA IONS Lewis bases can attack the co-ordinated water molecules. Theoretically, a proton can be removed from each water molecule turning the water from a neutral molecule to a negatively charged hydroxide ion. This affects the overall charge on the complex ion. [M(H2O)6]2+ (aq) [M(OH)(H2O)5]+ (aq) [M(OH)2(H2O)4](s) [M(OH)2(H2O)4](s) [M(OH)3(H2O)3]¯(aq) [M(OH)4(H2O)2]2- (aq) [M(OH)4(H2O)2]2- (aq) [M(OH)5(H2O)]3- (aq) [M(OH)6]4- (aq) In some cases, if the base is strong, further protons are removed and the precipitate dissolves as soluble anionic complexes such as [M(OH)6]3- are formed. Very weak bases H2O remove few protons Weak bases NH3, CO3 2- remove protons until precipitation Strong bases OH¯ can remove all the protons OH¯ H+ OH¯ H+ OH¯ H+ OH¯ H+ OH¯ H+ OH¯ H+ Precipitated
HYDROLYSIS OF HEXAAQUA IONSHYDROLYSIS OF HEXAAQUA IONS Lewis bases can attack the co-ordinated water molecules. Theoretically, a proton can be removed from each water molecule turning the water from a neutral molecule to a negatively charged hydroxide ion. This affects the overall charge on the complex ion. [M(H2O)6]2+ (aq) [M(OH)(H2O)5]+ (aq) [M(OH)2(H2O)4](s) [M(OH)2(H2O)4](s) [M(OH)3(H2O)3]¯(aq) [M(OH)4(H2O)2]2- (aq) [M(OH)4(H2O)2]2- (aq) [M(OH)5(H2O)]3- (aq) [M(OH)6]4- (aq) AMPHOTERIC CHARACTER Metal ions of 3+ charge have a high charge density and their hydroxides can dissolve in both acid and alkali. [M(H2O)6]3+ (aq) [M(OH)3(H2O)3](s) [M(OH)6]3- (aq) OH¯ H+ OH¯ H+ OH¯ H+ OH¯ H+ OH¯ H+ OH¯ H+ Precipitated OH¯H+ Insoluble SolubleSoluble
STABILITY CONSTANTSSTABILITY CONSTANTS Definition The stability constant, Kstab, of a complex ion is the equilibrium constant for the formation of the complex ion in a solvent from its constituent ions.
STABILITY CONSTANTSSTABILITY CONSTANTS Definition The stability constant, Kstab, of a complex ion is the equilibrium constant for the formation of the complex ion in a solvent from its constituent ions. In the reaction [M(H2O)6]2+ (aq) + 6X¯(aq) [MX6]4– (aq) + 6H2O(l)
STABILITY CONSTANTSSTABILITY CONSTANTS Definition The stability constant, Kstab, of a complex ion is the equilibrium constant for the formation of the complex ion in a solvent from its constituent ions. In the reaction [M(H2O)6]2+ (aq) + 6X¯(aq) [MX6]4– (aq) + 6H2O(l) the expression for the stability constant is Kstab = [ [MX6 4– ](aq) ] [ [M(H2O)6]2+ (aq) ] [ X¯(aq) ]6
STABILITY CONSTANTSSTABILITY CONSTANTS Definition The stability constant, Kstab, of a complex ion is the equilibrium constant for the formation of the complex ion in a solvent from its constituent ions. In the reaction [M(H2O)6]2+ (aq) + 6X¯(aq) [MX6]4– (aq) + 6H2O(l) the expression for the stability constant is Kstab = [ [MX6 4– ](aq) ] [ [M(H2O)6]2+ (aq) ] [ X¯(aq) ]6 The concentration of X¯(aq) appears to the power of 6 because there are six of the ions in the equation. Note that the water isn’t included; it is in such overwhelming quantity that its concentration can be regarded as ‘constant’.
STABILITY CONSTANTSSTABILITY CONSTANTS Because ligand exchange involves a series of equilibria, each step in the process has a different stability constant… Kstab / dm3 mol-1 [Co(H2O)6]2+ (aq) + NH3(aq) [Co(NH3)(H2O)5]2+ (aq) + H2O(l) K1 = 1.02 x 10-2 [Co(NH3)(H2O)5]2+ (aq) + NH3(aq) [Co(NH3)2(H2O)4]2+ (aq) + H2O(l) K2 = 3.09 x 10-2 [Co(NH3)2(H2O)4]2+ (aq) + NH3(aq) [Co(NH3)3(H2O)3]2+ (aq) + H2O(l) K3 = 1.17 x 10-1 [Co(NH3)3(H2O)3]2+ (aq) + NH3(aq) [Co(NH3)4(H2O)2]2+ (aq) + H2O(l) K4 = 2.29 x 10-1 [Co(NH3)4(H2O)2]2+ (aq) + NH3(aq) [Co(NH3)5(H2O)]2+ (aq) + H2O(l) K5 = 8.70 x 10-1 etc
STABILITY CONSTANTSSTABILITY CONSTANTS Because ligand exchange involves a series of equilibria, each step in the process has a different stability constant… Kstab / dm3 mol-1 [Co(H2O)6]2+ (aq) + NH3(aq) [Co(NH3)(H2O)5]2+ (aq) + H2O(l) K1 = 1.02 x 10-2 [Co(NH3)(H2O)5]2+ (aq) + NH3(aq) [Co(NH3)2(H2O)4]2+ (aq) + H2O(l) K2 = 3.09 x 10-2 [Co(NH3)2(H2O)4]2+ (aq) + NH3(aq) [Co(NH3)3(H2O)3]2+ (aq) + H2O(l) K3 = 1.17 x 10-1 [Co(NH3)3(H2O)3]2+ (aq) + NH3(aq) [Co(NH3)4(H2O)2]2+ (aq) + H2O(l) K4 = 2.29 x 10-1 [Co(NH3)4(H2O)2]2+ (aq) + NH3(aq) [Co(NH3)5(H2O)]2+ (aq) + H2O(l) K5 = 8.70 x 10-1 etc The overall stability constant is simply the equilibrium constant for the total reaction. It is found by multiplying the individual stability constants... k1 x k2 x k3 x k4 ... etc Kstab or pKstab? For an easier comparison, the expression pKstab is often used… pKstab = -log10Kstab
STABILITY CONSTANTSSTABILITY CONSTANTS Because ligand exchange involves a series of equilibria, each step in the process has a different stability constant… Kstab / dm3 mol-1 [Co(H2O)6]2+ (aq) + NH3(aq) [Co(NH3)(H2O)5]2+ (aq) + H2O(l) K1 = 1.02 x 10-2 [Co(NH3)(H2O)5]2+ (aq) + NH3(aq) [Co(NH3)2(H2O)4]2+ (aq) + H2O(l) K2 = 3.09 x 10-2 [Co(NH3)2(H2O)4]2+ (aq) + NH3(aq) [Co(NH3)3(H2O)3]2+ (aq) + H2O(l) K3 = 1.17 x 10-1 [Co(NH3)3(H2O)3]2+ (aq) + NH3(aq) [Co(NH3)4(H2O)2]2+ (aq) + H2O(l) K4 = 2.29 x 10-1 [Co(NH3)4(H2O)2]2+ (aq) + NH3(aq) [Co(NH3)5(H2O)]2+ (aq) + H2O(l) K5 = 8.70 x 10-1 etc Summary • The larger the stability constant, the further the reaction lies to the right • Complex ions with large stability constants are more stable • Stability constants are often given as pKstab • Complex ions with smaller pKstab values are more stable
REACTION TYPESREACTION TYPES The examples aim to show typical properties of transition metals and their compounds. One typical properties of transition elements is their ability to form complex ions. Complex ions consist of a central metal ion surrounded by co-ordinated ions or molecules known as ligands. This can lead to changes in ... • colour • co-ordination number • shape • stability to oxidation or reduction Reaction types ACID-BASE LIGAND SUBSTITUTION PRECIPITATION REDOX A-B LS OX Ppt RED REDOX
REACTION TYPESREACTION TYPES The examples aim to show typical properties of transition metals and their compounds. LOOK FOR... substitution reactions of complex ions variation in oxidation state of transition metals the effect of ligands on co-ordination number and shape increased acidity of M3+ over M2+ due to the increased charge density differences in reactivity of M3+ and M2+ ions with OH¯ and NH3 the reason why M3+ ions don’t form carbonates amphoteric character in some metal hydroxides (Al3+ and Cr3+ ) the effect a ligand has on the stability of a particular oxidation state
REACTIONS OF COBALT(II)REACTIONS OF COBALT(II) • aqueous solutions contain the pink, octahedral hexaaquacobalt(II) ion • hexaaqua ions can also be present in solid samples of the hydrated salts • as a 2+ ion, the solutions are weakly acidic but protons can be removed by bases... OH¯ [Co(H2O)6]2+ (aq) + 2OH¯(aq) ——> [Co(OH)2(H2O)4](s) + 2H2O(l) pink, octahedral blue / pink ppt. soluble in XS NaOH ALL hexaaqua ions precipitate a hydroxide with OH¯(aq). Some re-dissolve in excess NaOH A-B
REACTIONS OF COBALT(II)REACTIONS OF COBALT(II) NH3 [Co(H2O)6]2+ (aq) + 2NH3(aq) ——> [Co(OH)2(H2O)4](s) + 2NH4 + (aq) ALL hexaaqua ions precipitate a hydroxide with NH3 (aq). It removes protons A-B
REACTIONS OF COBALT(II)REACTIONS OF COBALT(II) NH3 [Co(H2O)6]2+ (aq) + 2NH3(aq) ——> [Co(OH)2(H2O)4](s) + 2NH4 + (aq) ALL hexaaqua ions precipitate a hydroxide with NH3 (aq). It removes protons Some hydroxides redissolve in excess NH3(aq) as ammonia substitutes as a ligand. [Co(OH)2(H2O)4](s) + 6NH3(aq) ——> [Co(NH3)6]2+ (aq) + 4H2O(l) + 2OH¯(aq) A-B LS
REACTIONS OF COBALT(II)REACTIONS OF COBALT(II) NH3 [Co(H2O)6]2+ (aq) + 2NH3(aq) ——> [Co(OH)2(H2O)4](s) + 2NH4 + (aq) ALL hexaaqua ions precipitate a hydroxide with NH3 (aq). It removes protons Some hydroxides redissolve in excess NH3(aq) as ammonia substitutes as a ligand. [Co(OH)2(H2O)4](s) + 6NH3(aq) ——> [Co(NH3)6]2+ (aq) + 4H2O(l) + 2OH¯(aq) but ... ammonia ligands make the Co(II) state unstable. Air oxidises Co(II) to Co(III) [Co(NH3)6]2+ (aq) ——> [Co(NH3)6]3+ (aq) + e¯ yellow / brown octahedral red / brown octahedral A-B LS OX
REACTIONS OF COBALT(II)REACTIONS OF COBALT(II) CO3 2- [Co(H2O)6]2+ (aq) + CO3 2- (aq) ——> CoCO3(s) + 6H2O(l) mauve ppt. Hexaaqua ions of metals with charge 2+ precipitate a carbonate but heaxaaqua ions with a 3+ charge don’t. Ppt
REACTIONS OF COBALT(II)REACTIONS OF COBALT(II) CO3 2- [Co(H2O)6]2+ (aq) + CO3 2- (aq) ——> CoCO3(s) + 6H2O(l) mauve ppt. Hexaaqua ions of metals with charge 2+ precipitate a carbonate but heaxaaqua ions with a 3+ charge don’t. Cl¯ [Co(H2O)6]2+ (aq) + 4Cl¯(aq) ——> [CoCl4]2- (aq) + 6H2O(l) pink, octahedral blue, tetrahedral • Cl¯ ligands are larger than H2O • Cl¯ ligands are negatively charged - H2O ligands are neutral • the complex is more stable if tetrahedral - less repulsion between ligands • adding excess water reverses the reaction LS Ppt
REACTIONS OF COPPER(II)REACTIONS OF COPPER(II) Aqueous solutions of copper(II) contain the blue, octahedral hexaaquacopper(II) ion Most substitution reactions are similar to cobalt(II). OH¯ [Cu(H2O)6]2+ (aq) + 2OH¯(aq) ——> [Cu(OH)2(H2O)4](s) + 2H2O(l) blue, octahedral pale blue ppt. insoluble in XS NaOH A-B
REACTIONS OF COPPER(II)REACTIONS OF COPPER(II) Aqueous solutions of copper(II) contain the blue, octahedral hexaaquacopper(II) ion Most substitution reactions are similar to cobalt(II). OH¯ [Cu(H2O)6]2+ (aq) + 2OH¯(aq) ——> [Cu(OH)2(H2O)4](s) + 2H2O(l) blue, octahedral pale blue ppt. insoluble in XS NaOH NH3 [Cu(H2O)6]2+ (aq) + 2NH3(aq) ——> [Cu(OH)2(H2O)4](s) + 2NH4 + (aq) blue ppt. soluble in excess NH3 then [Cu(OH)2(H2O)4](s) + 4NH3(aq) ——> [Cu(NH3)4(H2O)2]2+ (aq) + 2H2O(l) + 2OH¯(aq) royal blue NOTE THE FORMULA A-B A-B LS
REACTIONS OF COPPER(II)REACTIONS OF COPPER(II) Aqueous solutions of copper(II) contain the blue, octahedral hexaaquacopper(II) ion Most substitution reactions are similar to cobalt(II). OH¯ [Cu(H2O)6]2+ (aq) + 2OH¯(aq) ——> [Cu(OH)2(H2O)4](s) + 2H2O(l) blue, octahedral pale blue ppt. insoluble in XS NaOH NH3 [Cu(H2O)6]2+ (aq) + 2NH3(aq) ——> [Cu(OH)2(H2O)4](s) + 2NH4 + (aq) blue ppt. soluble in excess NH3 then [Cu(OH)2(H2O)4](s) + 4NH3(aq) ——> [Cu(NH3)4(H2O)2]2+ (aq) + 2H2O(l) + 2OH¯(aq) royal blue NOTE THE FORMULA CO3 2- [Cu(H2O)6]2+ (aq) + CO3 2- (aq) ——> CuCO3(s) + 6H2O(l) blue ppt. A-B A-B LS Ppt
REACTIONS OF COPPER(II)REACTIONS OF COPPER(II) Cl¯ [Cu(H2O)6]2+ (aq) + 4Cl¯(aq) ——> [CuCl4]2- (aq) + 6H2O(l) yellow, tetrahedral • Cl¯ ligands are larger than H2O and are charged • the complex is more stable if the shape changes to tetrahedral • adding excess water reverses the reaction I¯ 2Cu2+ (aq) + 4I¯(aq) ——> 2CuI(s) + I2(aq) off - white ppt. • a redox reaction • used in the volumetric analysis of copper using sodium thiosulphate LS REDOX
REACTIONS OF COPPER(I)REACTIONS OF COPPER(I) The aqueous chemistry of copper(I) is unstable compared to copper(0) and copper (II). Cu+ (aq) + e¯ ——> Cu(s) E° = + 0.52 V Cu2+ (aq) + e¯ ——> Cu+ (aq) E° = + 0.15 V subtracting 2Cu+ (aq) ——> Cu(s) + Cu2+ (aq) E° = + 0.37 V This is an example of DISPROPORTIONATION where one species is simultaneously oxidised and reduced to more stable forms. This explains why the aqueous chemistry of copper(I) is very limited. Copper(I) can be stabilised by formation of complexes.
REACTIONS OF CHROMIUM(III)REACTIONS OF CHROMIUM(III) Chromium(III) ions are typical of M3+ ions in this block. Aqueous solutions contain the violet, octahedral hexaaquachromium(III) ion. OH¯ [Cr(H2O)6]3+ (aq) + 3OH¯(aq) ——> [Cr(OH)3(H2O)3](s) + 3H2O(l) violet, octahedral green ppt. soluble in XS NaOH As with all hydroxides the precipitate reacts with acid [Cr(OH)3(H2O)3](s) + 3H+ (aq) ——> [Cr(H2O)6]3+ (aq) being a 3+ hydroxide it is AMPHOTERIC as it dissolves in excess alkali [Cr(OH)3(H2O)3](s) + 3OH¯(aq) ——> [Cr(OH)6]3- (aq) + 3H2O(l) green, octahedral A-B A-B A-B
REACTIONS OF CHROMIUM(III)REACTIONS OF CHROMIUM(III) CO3 2- 2 [Cr(H2O)6]3+ (aq) + 3CO3 2- (aq) ——> 2[Cr(OH)3(H2O)3](s) + 3H2O(l) + 3CO2(g) The carbonate is not precipitated but the hydroxide is. high charge density of M3+ makes the solution too acidic to form the carbonate CARBON DIOXIDE IS EVOLVED. A-B
REACTIONS OF CHROMIUM(III)REACTIONS OF CHROMIUM(III) CO3 2- 2 [Cr(H2O)6]3+ (aq) + 3CO3 2- (aq) ——> 2[Cr(OH)3(H2O)3](s) + 3H2O(l) + 3CO2(g) The carbonate is not precipitated but the hydroxide is. high charge density of M3+ makes the solution too acidic to form the carbonate CARBON DIOXIDE IS EVOLVED. NH3 [Cr(H2O)6]3+ (aq) + 3NH3(aq) ——> [Cr(OH)3(H2O)3](s) + 3NH4 + (aq) green ppt. soluble in XS NH3 With EXCESS AMMONIA, the precipitate redissolves [Cr(OH)3(H2O)3](s) + 6NH3(aq) ——> [Cr(NH3)6]3+ (aq) + 3H2O(l) + 3OH¯(aq) LS A-B A-B
REACTIONS OF CHROMIUM(III)REACTIONS OF CHROMIUM(III) Oxidation In the presence of alkali, Cr(III) is unstable and can be oxidised to Cr(VI) 2Cr3+ (aq) + 3H2O2(l) + 10OH¯(aq) ——> 2CrO4 2- (aq) + 8H2O(l) green yellow Acidification of the yellow chromate will produce the orange dichromate(VI) ion Reduction Chromium(III) can be reduced to the less stable chromium(II) by zinc in acid 2 [Cr(H2O)6]3+ (aq) + Zn(s) ——> 2 [Cr(H2O)6]2+ (aq) + Zn2+ (aq) green blue OX RED
REACTIONS OF CHROMIUM(VI)REACTIONS OF CHROMIUM(VI) Occurrence dichromate (VI) Cr2O7 2- orange chromate (VI) CrO4 2- yellow Interconversion dichromate is stable in acid solution chromate is stable in alkaline solution in alkali Cr2O7 2- (aq) + 2OH¯(aq) 2CrO4 2- (aq) + H2O(l) in acid 2CrO4 2- (aq) + 2H+ (aq) Cr2O7 2- (aq) + H2O(l)
CONTENTSCONTENTS OXIDATION REACTIONS OF CHROMIUM(VI)OXIDATION REACTIONS OF CHROMIUM(VI) Being in the highest oxidation state (+6), chromium(VI) will be an oxidising agent. In acidic solution, dichromate is widely used in both organic (oxidation of alcohols) and inorganic chemistry. It can also be used as a volumetric reagent but with special indicators as its colour change (orange to green) makes the end point hard to observe. Cr2O7 2- (aq) + 14H+ (aq) + 6e¯ ——> 2Cr3+ (aq) + 7H2O(l) [ E° = +1.33 V ] orange green • Its E° value is lower than that of Cl2 (1.36V) so can be used in the presence of Cl¯ ions • MnO4¯ (E° = 1.52V) oxidises chloride in HCl so must be acidified with sulphuric acid • chromium(VI) can be reduced back to chromium(III) using zinc in acid solution
REACTIONS OF MANGANESE(VII)REACTIONS OF MANGANESE(VII) • in its highest oxidation state therefore Mn(VII) will be an oxidising agent • occurs in the purple, tetraoxomanganate(VII) (permanganate) ion (MnO4¯) • acts as an oxidising agent in acidic or alkaline solution acidic MnO4¯(aq) + 8H+ (aq) + 5e¯ ——> Mn2+ (aq) + 4H2O(l) E° = + 1.52 V N.B. Acidify with dilute H2SO4 NOT dilute HCl alkaline MnO4¯(aq) + 2H2O(l) + 3e¯ ——> MnO2(s) + 4OH¯(aq) E° = + 0.59 V
VOLUMETRIC USE OF MANGANATE(VII)VOLUMETRIC USE OF MANGANATE(VII) Potassium manganate(VII) in acidic (H2SO4) solution is extremely useful for carrying out redox volumetric analysis. MnO4¯(aq) + 8H+ (aq) + 5e¯ ——> Mn2+ (aq) + 4H2O(l) E° = + 1.52 V It must be acidified with dilute sulphuric acid as MnO4¯ is powerful enough to oxidise the chloride ions in hydrochloric acid. It is used to estimate iron(II), hydrogen peroxide, ethanedioic (oxalic) acid and ethanedioate (oxalate) ions. The last two titrations are carried out above 60°C due to the slow rate of reaction. No indicator is required; the end point being the first sign of a permanent pale pink colour. Iron(II) MnO4¯(aq) + 8H+ (aq) + 5Fe2+ (aq) ——> Mn2+ (aq) + 5Fe3+ (aq) + 4H2O(l) this means that moles of Fe2+ = 5 moles of MnO4¯ 1
REACTIONS OF IRON(II)REACTIONS OF IRON(II) When iron reacts with acids it gives rise to iron(II) (ferrous) salts. Aqueous solutions of such salts contain the pale green, octahedral hexaaquairon(II) ion OH¯ [Fe(H2O)6]2+ (aq) + 2OH¯(aq) ——> [Fe(OH)2(H2O)4](s) + 2H2O(l) pale green dirty green ppt. it only re-dissolves in very conc. OH¯ but... it slowly turns a rusty brown colour due to oxidation by air to iron(III) increasing the pH renders iron(II) unstable. Fe(OH)2(s) + OH¯(aq) ——> Fe(OH)3(s) + e¯ dirty green rusty brown NH3 Iron(II) hydroxide precipitated, insoluble in excess ammonia CO3 2- Off-white coloured iron(II) carbonate, FeCO3, precipitated A-B A-B OX Ppt
CONTENTSCONTENTS REACTIONS OF IRON(II)REACTIONS OF IRON(II) Volumetric Iron(II) can be analysed by titration with potassium manganate(VII) in acidic (H2SO4) solution. No indicator is required. MnO4¯(aq) + 8H+ (aq) + 5Fe2+ (aq) ——> Mn2+ (aq) + 5Fe3+ (aq) + 4H2O(l) this means that moles of Fe2+ = 5 moles of MnO4¯ 1
REACTIONS OF IRON(III)REACTIONS OF IRON(III) Aqueous solutions contain the yellow-green, octahedral hexaaquairon(III) ion OH¯ [Fe(H2O)6]3+ (aq) + 3OH¯(aq) ——> [Fe(OH)3(H2O)3](s) + 3H2O(l) yellow rusty-brown ppt. insoluble in XS A-B
REACTIONS OF IRON(III)REACTIONS OF IRON(III) Aqueous solutions contain the yellow-green, octahedral hexaaquairon(III) ion OH¯ [Fe(H2O)6]3+ (aq) + 3OH¯(aq) ——> [Fe(OH)3(H2O)3](s) + 3H2O(l) yellow rusty-brown ppt. insoluble in XS CO3 2- 2[Fe(H2O)6]3+ (aq) + 3CO3 2- (aq) ——> 2[Fe(OH)3(H2O)3](s) + 3H2O(l) + 3CO2(g) rusty-brown ppt. The carbonate is not precipitated but the hydroxide is; the high charge density of M3+ makes the solution too acidic to form a carbonate CARBON DIOXIDE EVOLVED. A-B A-B
REACTIONS OF IRON(III)REACTIONS OF IRON(III) Aqueous solutions contain the yellow-green, octahedral hexaaquairon(III) ion OH¯ [Fe(H2O)6]3+ (aq) + 3OH¯(aq) ——> [Fe(OH)3(H2O)3](s) + 3H2O(l) yellow rusty-brown ppt. insoluble in XS CO3 2- 2[Fe(H2O)6]3+ (aq) + 3CO3 2- (aq) ——> 2[Fe(OH)3(H2O)3](s) + 3H2O(l) + 3CO2(g) rusty-brown ppt. The carbonate is not precipitated but the hydroxide is; the high charge density of M3+ makes the solution too acidic to form a carbonate CARBON DIOXIDE EVOLVED. NH3 [Fe(H2O)6]3+ (aq) + 3NH3(aq) ——> [Fe(OH)3(H2O)3](s) + 3NH4 + (aq) rusty-brown ppt. insoluble in XS A-B A-B A-B
REACTIONS OF IRON(III)REACTIONS OF IRON(III) Aqueous solutions contain the yellow-green, octahedral hexaaquairon(III) ion OH¯ [Fe(H2O)6]3+ (aq) + 3OH¯(aq) ——> [Fe(OH)3(H2O)3](s) + 3H2O(l) yellow rusty-brown ppt. insoluble in XS CO3 2- 2[Fe(H2O)6]3+ (aq) + 3CO3 2- (aq) ——> 2[Fe(OH)3(H2O)3](s) + 3H2O(l) + 3CO2(g) rusty-brown ppt. The carbonate is not precipitated but the hydroxide is; the high charge density of M3+ makes the solution too acidic to form a carbonate CARBON DIOXIDE EVOLVED. NH3 [Fe(H2O)6]3+ (aq) + 3NH3(aq) ——> [Fe(OH)3(H2O)3](s) + 3NH4 + (aq) rusty-brown ppt. insoluble in XS SCN¯ [Fe(H2O)6]3+ (aq) + SCN¯(aq) ——> [Fe(SCN)(H2O)5]2+ (aq) + H2O(l) blood-red colour Very sensitive; BLOOD RED COLOUR confirms Fe(III). No reaction with Fe(II) A-B A-B LS A-B
REACTIONS OF SILVER(I)REACTIONS OF SILVER(I) • aqueous solutions contains the colourless, linear, diammine silver(I) ion • formed when silver halides dissolve in ammonia eg AgCl(s) + 2NH3(aq) ——> [Ag(NH3)2]+ (aq) + Cl¯(aq) [Ag(SO3)2]3- Formed when silver salts are dissolved in sodium thiosulphate "hypo" solution. Important in photographic fixing. Any silver bromide not exposed to light is dissolved away leaving the black image of silver as the negative. AgBr + 2S2O3 2- ——> [Ag(S2O3)2]3- + Br¯ [Ag(CN)2]¯ Formed when silver salts are dissolved in sodium or potassium cyanide the solution used for silver electroplating [Ag(NH3)2]+ Used in Tollen’s reagent (SILVER MIRROR TEST) Tollen’s reagent is used to differentiate between aldehydes and ketones. Aldehydes produce a silver mirror on the inside of the test tube Formed when silver halides dissolve in ammonia - TEST FOR HALIDES
REACTIONS OF VANADIUMREACTIONS OF VANADIUM Reduction using zinc in acidic solution shows the various oxidation states of vanadium. Vanadium(V) VO2+ (aq) + 2H+ (aq) + e¯ ——> VO2+ (aq) + H2O(l) yellow blue Vanadium(IV) VO2+ (aq) + 2H+ (aq) + e¯ ——> V3+ (aq) + H2O(l) blue blue/green Vanadium(III) V3+ (aq) + e¯ ——> V2+ (aq) blue/green lavender
OXIDATION & REDUCTION -OXIDATION & REDUCTION - A SUMMARYA SUMMARY Oxidation • complex transition metal ions are stable in acid solution • complex ions tend to be less stable in alkaline solution • in alkaline conditions they form neutral hydroxides and/or anionic complexes • it is easier to remove electrons from neutral or negatively charged species • alkaline conditions are usually required e.g. Fe(OH)2(s) + OH¯(aq) ——> Fe(OH)3(s) + e¯ Co(OH)2(s) + OH¯(aq) ——> Co(OH)3(s) + e¯ 2Cr3+ (aq) + 3H2O2(l) + 10OH¯(aq) ——> 2CrO4 2- (aq) + 8H2O(l) • Solutions of cobalt(II) can be oxidised by air under ammoniacal conditions [Co(NH3)6]2+ (aq) ——> [Co(NH3)6]3+ (aq) + e¯
OXIDATION & REDUCTION -OXIDATION & REDUCTION - A SUMMARYA SUMMARY Oxidation • complex transition metal ions are stable in acid solution • complex ions tend to be less stable in alkaline solution • in alkaline conditions they form neutral hydroxides and/or anionic complexes • it is easier to remove electrons from neutral or negatively charged species • alkaline conditions are usually required e.g. Fe(OH)2(s) + OH¯(aq) ——> Fe(OH)3(s) + e¯ Co(OH)2(s) + OH¯(aq) ——> Co(OH)3(s) + e¯ 2Cr3+ (aq) + 3H2O2(l) + 10OH¯(aq) ——> 2CrO4 2- (aq) + 8H2O(l) • Solutions of cobalt(II) can be oxidised by air under ammoniacal conditions [Co(NH3)6]2+ (aq) ——> [Co(NH3)6]3+ (aq) + e¯ Reduction • Zinc metal is used to reduce transition metal ions to lower oxidation states • It acts in acid solution as follows... Zn(s) ——> Zn2+ (aq) + 2e¯ e.g. it reduces iron(III) to iron(II) vanadium(V) to vanadium (IV) to vanadium(III)
REACTIONS OF ALUMINIUMREACTIONS OF ALUMINIUM • aluminium is not a transition metal as it doesn’t make use of d orbitals • BUT, due to a high charge density, aluminium ions behave as typical M3+ ions • aqueous solutions contain the colourless, octahedral hexaaquaaluminium(III) ion OH¯ [Al(H2O)6]3+ (aq) + 3OH¯(aq) ——> [Al(OH)3(H2O3](s) + 3H2O(l) colourless, octahedral white ppt. soluble in XS NaOH As with all hydroxides the precipitate reacts with acid [Al(OH)3(H2O)3](s) + 3H+ (aq) ——> [Al(H2O)6]3+ (aq) being a 3+ hydroxide it is AMPHOTERIC and dissolves in excess alkali [Al(OH)3(H2O)3](s) + 3OH¯(aq) ——> [Al(OH)6]3- (aq) + 3H2O(l) colourless, octahedral CO3 2- 2 [Al(H2O)6]3+ (aq) + 3CO3 2- (aq) ——> 2[Al(OH)3(H2O)3](s) + 3H2O(l) + 3CO2(g) As with 3+ ions, the carbonate is not precipitated but the hydroxide is. NH3 [Al(H2O)6]3+ (aq) + 3NH3(aq) ——> [Al(OH)3(H2O)3](s) + 3NH4 + (aq) white ppt. insoluble in XS NH3 A-B A-B A-B A-B A-B
© 2009 JONATHAN HOPTON & KNOCKHARDY PUBLISHING© 2009 JONATHAN HOPTON & KNOCKHARDY PUBLISHING THETHE ENDEND AN INTRODUCTION TOAN INTRODUCTION TO TRANSITION METALTRANSITION METAL COMPLEXESCOMPLEXES

More Related Content

PPTX
HYBRIDISATION : Derivation Of Wave Function For The Following Orbital Hybridi...
prasad karekar
 
PPTX
Crystal field stabilization energy
Dr. Krishna Swamy. G
 
PPTX
Organometallic Chemistry
Manju Sebastian
 
PPT
Dioxygen complexes, dioxygen as ligand
Geeta Tewari
 
PPSX
Mossbauer spectroscopy - Principles and applications
SANTHANAM V
 
PPTX
Structure types of crystals
Picasa_10
 
PPTX
Organometallic chemistry
Shivaji Burungale
 
PPTX
Lanthanide contraction
NSSWAMIKARANAM
 
HYBRIDISATION : Derivation Of Wave Function For The Following Orbital Hybridi...
prasad karekar
 
Crystal field stabilization energy
Dr. Krishna Swamy. G
 
Organometallic Chemistry
Manju Sebastian
 
Dioxygen complexes, dioxygen as ligand
Geeta Tewari
 
Mossbauer spectroscopy - Principles and applications
SANTHANAM V
 
Structure types of crystals
Picasa_10
 
Organometallic chemistry
Shivaji Burungale
 
Lanthanide contraction
NSSWAMIKARANAM
 

What's hot (20)

PPTX
Tanabe sugano diagram
Afrina Jasy
 
PPTX
Trans effect And Its Applications
Imaginative Brain Science
 
PPTX
Slater rules
Mithil Fal Desai
 
PPTX
Ligand substitution reactions
BISWAJIT MORAN
 
PPTX
Aromaticity in benzenoid and non-benzenoid compunds
SPCGC AJMER
 
PPTX
Zero field splitting
Naveed Bashir
 
PDF
Ionic Liquids : Green solvents for the future
Mrudang Thakor
 
PDF
Aromaticity
meenalgupta30
 
PPTX
.Electron diffraction for m.sc, student complete unit
shyam sunder pandiya
 
PPTX
Ligand substitution reactions
Pallavi Kumbhar
 
PPTX
Cryptates
Bluescience1
 
PPTX
Bonding in coordination compound(werners theory)
Shri Shankaracharya College, Bhilai,Junwani
 
PPT
Organometallic compounds
Arvind Singh Heer
 
PPT
Dinitrogen complexes
Geeta Tewari
 
PPTX
Mossbauer Spectroscopy
MANISHSAHU106
 
PPTX
Organometallic Reactions and Catalysis
Rajat Ghalta
 
PPTX
Kinetics of Chain reaction
Saiva Bhanu Kshatriya College, Aruppukottai.
 
PPTX
Inner sphere mechanism
Vandita Raj
 
PPTX
Metal carbonyls
satyabrata sendh
 
PPTX
REDOX REACTION : inner & outer sphere Complimentary & non-complimentary reaction
Sachin Kale
 
Tanabe sugano diagram
Afrina Jasy
 
Trans effect And Its Applications
Imaginative Brain Science
 
Slater rules
Mithil Fal Desai
 
Ligand substitution reactions
BISWAJIT MORAN
 
Aromaticity in benzenoid and non-benzenoid compunds
SPCGC AJMER
 
Zero field splitting
Naveed Bashir
 
Ionic Liquids : Green solvents for the future
Mrudang Thakor
 
Aromaticity
meenalgupta30
 
.Electron diffraction for m.sc, student complete unit
shyam sunder pandiya
 
Ligand substitution reactions
Pallavi Kumbhar
 
Cryptates
Bluescience1
 
Bonding in coordination compound(werners theory)
Shri Shankaracharya College, Bhilai,Junwani
 
Organometallic compounds
Arvind Singh Heer
 
Dinitrogen complexes
Geeta Tewari
 
Mossbauer Spectroscopy
MANISHSAHU106
 
Organometallic Reactions and Catalysis
Rajat Ghalta
 
Kinetics of Chain reaction
Saiva Bhanu Kshatriya College, Aruppukottai.
 
Inner sphere mechanism
Vandita Raj
 
Metal carbonyls
satyabrata sendh
 
REDOX REACTION : inner & outer sphere Complimentary & non-complimentary reaction
Sachin Kale
 
Ad

Similar to Transition metal complexes unit 1 (20)

PPT
Elektrolit dan Nonelek
Annik Qurniawati
 
PPTX
Reactions in aqueous solution; solubility rules, molecular and ionic equation...
esperansashitumbulen
 
PPTX
Acids bases and salts
Chakri Pani
 
PPTX
C4-Chemical-changes- (1).pptx
Priya282836
 
PPT
15saltspp.ppt
ThinhTranKhang
 
PPT
Chapter 16
ewalenta
 
PPT
CHAPTER 16 Slide Deck Acis & Bases Inorganic chemistry
lesterbernardino5
 
PPTX
Acids and Bses
armindaortiz
 
PDF
Ch4 Reactions in Aqueous Solution
Sa'ib J. Khouri
 
PPTX
Y13 acids & bases lta 2017
lyndena
 
PPTX
sch3u_u4_lesson_5_acids_bases_and_ph.pptx
seok81
 
PPTX
(01)Acid and Base for biochemistry .pptx
seunnnade12
 
PPT
Chemistry - Chp 19 - Acids, Bases, and Salt - PowerPoints
Mel Anthony Pepito
 
PDF
Chemistry of Water_unique properties of water
ChimwemweGladysBanda
 
PPT
Diploma_I_Applied science(chemistry)U-III Acid & bases
Rai University
 
PPT
Chap 12 Acids and Bases (3) defintions s
fuat8
 
PPTX
lectures 17-20, Trimester 2, AY 22-23.pptx
ayeshafozan1
 
PPT
Chapter 8: Reactions in Aqueous Solution
Melissa McDonald
 
PPT
Acids-Bases-pH-PPT-2018.ppt.organic-chemistry
YvaMargaretRomanBala
 
PPT
Chapter 19
Malcolm Harrison
 
Elektrolit dan Nonelek
Annik Qurniawati
 
Reactions in aqueous solution; solubility rules, molecular and ionic equation...
esperansashitumbulen
 
Acids bases and salts
Chakri Pani
 
C4-Chemical-changes- (1).pptx
Priya282836
 
15saltspp.ppt
ThinhTranKhang
 
Chapter 16
ewalenta
 
CHAPTER 16 Slide Deck Acis & Bases Inorganic chemistry
lesterbernardino5
 
Acids and Bses
armindaortiz
 
Ch4 Reactions in Aqueous Solution
Sa'ib J. Khouri
 
Y13 acids & bases lta 2017
lyndena
 
sch3u_u4_lesson_5_acids_bases_and_ph.pptx
seok81
 
(01)Acid and Base for biochemistry .pptx
seunnnade12
 
Chemistry - Chp 19 - Acids, Bases, and Salt - PowerPoints
Mel Anthony Pepito
 
Chemistry of Water_unique properties of water
ChimwemweGladysBanda
 
Diploma_I_Applied science(chemistry)U-III Acid & bases
Rai University
 
Chap 12 Acids and Bases (3) defintions s
fuat8
 
lectures 17-20, Trimester 2, AY 22-23.pptx
ayeshafozan1
 
Chapter 8: Reactions in Aqueous Solution
Melissa McDonald
 
Acids-Bases-pH-PPT-2018.ppt.organic-chemistry
YvaMargaretRomanBala
 
Chapter 19
Malcolm Harrison
 
Ad

More from dean dundas (20)

PDF
Prezi test
dean dundas
 
PDF
Panel Discussion Guildeline
dean dundas
 
PPT
Point of view Grade 5
dean dundas
 
PPTX
Apresentar dados na forma de distribuição de frequências
dean dundas
 
PPTX
Apresentar dados na forma de distribuição de frequências
dean dundas
 
PPTX
Determinar frequências absoluta, relativa e relativa percentual
dean dundas
 
PPTX
O surgimento das zonas libertadas
dean dundas
 
PPTX
Cad program account
dean dundas
 
PPT
2a. structures, compression, torsion, shear, bending, tension, stress & ...
dean dundas
 
PPTX
Notesmaster Support Network Introduction
dean dundas
 
PDF
Notes on the Picaresque Novel
dean dundas
 
PPT
Brazilian independence
dean dundas
 
PPTX
Caribbean freedom peasantry- w. k. marshall
dean dundas
 
PPTX
Cams
dean dundas
 
PPT
10003553
dean dundas
 
PDF
Dimensions in engineering_drawings
dean dundas
 
PDF
17 surface roughness-and_machining_symbols_full
dean dundas
 
PDF
Instruction Verbs in Essay Questions
dean dundas
 
PDF
Siegfried Sassoon, Wilfred Owen & WWI
dean dundas
 
PDF
The Mother's Sons: Katharine Tynan's War Poetry
dean dundas
 
Prezi test
dean dundas
 
Panel Discussion Guildeline
dean dundas
 
Point of view Grade 5
dean dundas
 
Apresentar dados na forma de distribuição de frequências
dean dundas
 
Apresentar dados na forma de distribuição de frequências
dean dundas
 
Determinar frequências absoluta, relativa e relativa percentual
dean dundas
 
O surgimento das zonas libertadas
dean dundas
 
Cad program account
dean dundas
 
2a. structures, compression, torsion, shear, bending, tension, stress & ...
dean dundas
 
Notesmaster Support Network Introduction
dean dundas
 
Notes on the Picaresque Novel
dean dundas
 
Brazilian independence
dean dundas
 
Caribbean freedom peasantry- w. k. marshall
dean dundas
 
Cams
dean dundas
 
10003553
dean dundas
 
Dimensions in engineering_drawings
dean dundas
 
17 surface roughness-and_machining_symbols_full
dean dundas
 
Instruction Verbs in Essay Questions
dean dundas
 
Siegfried Sassoon, Wilfred Owen & WWI
dean dundas
 
The Mother's Sons: Katharine Tynan's War Poetry
dean dundas
 

Recently uploaded (20)

PDF
The Future of Telehealth: Engineering New Platforms for Care (www.kiu.ac.ug)
publication11
 
PDF
Is Earendel a Star Cluster?: Metal-poor Globular Cluster Progenitors at z ∼ 6
Sérgio Sacani
 
PPTX
gene cloning powerpoint for general biology 2
G17RodriguezJanelleA
 
PDF
Science Form five needed shit SCIENEce so
ArielLucifer1
 
PDF
From Molecular Interactions to Solubility in Deep Eutectic Solvents: Explorin...
Maciej Przybyłek
 
PPTX
Platelet disorders - thrombocytopenia.pptx
AnnaMarie531858
 
PDF
7.Physics_8_WBS_Electricity.pdfXFGXFDHFHG
LynetteGaniron1
 
PDF
Chapter 3 - Human Development Poweroint presentation
GOOGLE
 
PPTX
gene cloning powerpoint for general biology 2
G17RodriguezJanelleA
 
PDF
Cosmology using numerical relativity - what hapenned before big bang?
Sérgio Sacani
 
PPTX
ELISA(Enzyme linked immunosorbent assay)
asmithaasmitha376
 
PPTX
PMR- PPT.pptx for students and doctors tt
DiyaSajid2
 
PDF
Communicating Health Policies to Diverse Populations (www.kiu.ac.ug)
publication11
 
PPT
1. INTRODUCTION TO EPIDEMIOLOGY.pptx for community medicine
olawooreteslim
 
PPTX
congenital heart diseases of burao university.pptx
eapdiaziz
 
PPTX
Cells and Organs of the Immune System (Unit-2) - Majesh Sir.pptx
tkgauri1
 
PDF
5.Physics 8-WBS_Light.pdfFHDGJDJHFGHJHFTY
LynetteGaniron1
 
PPTX
GREEN FIELDS SCHOOL PPT ON HOLIDAY HOMEWORK
GandharvaVerma
 
PPTX
Presentation1 INTRODUCTION TO ENZYMES.pptx
JIBY2
 
PPTX
Substance Disorders- part different drugs change body
NizaAnne
 
The Future of Telehealth: Engineering New Platforms for Care (www.kiu.ac.ug)
publication11
 
Is Earendel a Star Cluster?: Metal-poor Globular Cluster Progenitors at z ∼ 6
Sérgio Sacani
 
gene cloning powerpoint for general biology 2
G17RodriguezJanelleA
 
Science Form five needed shit SCIENEce so
ArielLucifer1
 
From Molecular Interactions to Solubility in Deep Eutectic Solvents: Explorin...
Maciej Przybyłek
 
Platelet disorders - thrombocytopenia.pptx
AnnaMarie531858
 
7.Physics_8_WBS_Electricity.pdfXFGXFDHFHG
LynetteGaniron1
 
Chapter 3 - Human Development Poweroint presentation
GOOGLE
 
gene cloning powerpoint for general biology 2
G17RodriguezJanelleA
 
Cosmology using numerical relativity - what hapenned before big bang?
Sérgio Sacani
 
ELISA(Enzyme linked immunosorbent assay)
asmithaasmitha376
 
PMR- PPT.pptx for students and doctors tt
DiyaSajid2
 
Communicating Health Policies to Diverse Populations (www.kiu.ac.ug)
publication11
 
1. INTRODUCTION TO EPIDEMIOLOGY.pptx for community medicine
olawooreteslim
 
congenital heart diseases of burao university.pptx
eapdiaziz
 
Cells and Organs of the Immune System (Unit-2) - Majesh Sir.pptx
tkgauri1
 
5.Physics 8-WBS_Light.pdfFHDGJDJHFGHJHFTY
LynetteGaniron1
 
GREEN FIELDS SCHOOL PPT ON HOLIDAY HOMEWORK
GandharvaVerma
 
Presentation1 INTRODUCTION TO ENZYMES.pptx
JIBY2
 
Substance Disorders- part different drugs change body
NizaAnne
 

Transition metal complexes unit 1

  • 1. AN INTRODUCTION TOAN INTRODUCTION TO TRANSITION METALTRANSITION METAL COMPLEXESCOMPLEXES KNOCKHARDY PUBLISHINGKNOCKHARDY PUBLISHING 20082008 SPECIFICATIONSSPECIFICATIONS
  • 2. INTRODUCTION This Powerpoint show is one of several produced to help students understand selected topics at AS and A2 level Chemistry. It is based on the requirements of the AQA and OCR specifications but is suitable for other examination boards. Individual students may use the material at home for revision purposes or it may be used for classroom teaching if an interactive white board is available. Accompanying notes on this, and the full range of AS and A2 topics, are available from the KNOCKHARDY SCIENCE WEBSITE at... www.knockhardy.org.uk/sci.htm Navigation is achieved by... either clicking on the grey arrows at the foot of each page or using the left and right arrow keys on the keyboard KNOCKHARDY PUBLISHINGKNOCKHARDY PUBLISHING TRANSITION METALSTRANSITION METALS
  • 3. CONTENTS • Aqueous metal ions • Acidity of hexaaqua ions - stability constants • Introduction to the reactions of complexes • Reactions of cobalt • Reactions of copper • Reactions chromium • Reactions on manganese • Reactions of iron(II) • Reactions of iron(III) • Reactions of silver and vanadium • Reactions of aluminium TRANSITION METALSTRANSITION METALS
  • 4. THE AQUEOUS CHEMISTRY OF IONS - HYDROLYSISTHE AQUEOUS CHEMISTRY OF IONS - HYDROLYSIS when salts dissolve in water the ions are stabilised this is because water molecules are polar hydrolysis can occur and the resulting solution can become acidic the acidity of the resulting solution depends on the cation present the greater the charge density of the cation, the more acidic the solution cation charge ionic radius reaction with water / pH of chloride Na 1+ 0.095 nm Mg 2+ 0.065 nm Al 3+ 0.050 nm the greater charge density of the cation... the greater the polarising power and the more acidic the solution
  • 5. THE AQUEOUS CHEMISTRY OF IONS - HYDROLYSISTHE AQUEOUS CHEMISTRY OF IONS - HYDROLYSIS when salts dissolve in water the ions are stabilised this is because water molecules are polar hydrolysis can occur and the resulting solution can become acidic the acidity of the resulting solution depends on the cation present the greater the charge density of the cation, the more acidic the solution cation charge ionic radius reaction with water / pH of chloride Na 1+ 0.095 nm dissolves 7 Mg 2+ 0.065 nm slight hydrolysis Al 3+ 0.050 nm vigorous hydrolysis the greater charge density of the cation... the greater the polarising power and the more acidic the solution
  • 6. THE AQUEOUS CHEMISTRY OF IONSTHE AQUEOUS CHEMISTRY OF IONS Theory aqueous metal ions attract water molecules many have six water molecules surrounding them these are known as hexaaqua ions they are octahedral in shape water acts as a Lewis Base – a lone pair donor water forms a co-ordinate bond to the metal ion metal ions accept the lone pair - Lewis Acids
  • 7. THE AQUEOUS CHEMISTRY OF IONSTHE AQUEOUS CHEMISTRY OF IONS Theory aqueous metal ions attract water molecules many have six water molecules surrounding them these are known as hexaaqua ions they are octahedral in shape water acts as a Lewis Base – a lone pair donor water forms a co-ordinate bond to the metal ion metal ions accept the lone pair - Lewis Acids Acidity as charge density increases, the cation has a greater attraction for water the attraction extends to the shared pair of electrons in water’s O-H bonds the electron pair is pulled towards the O, making the bond more polar this makes the H more acidic (more δ+) it can then be removed by solvent water molecules to form H3O+ (aq).
  • 8. HYDROLYSIS -HYDROLYSIS - EQUATIONSEQUATIONS M2+ ions [M(H2O)6]2+ (aq) + H2O(l) [M(H2O)5(OH)]+ (aq) + H3O+ (aq) the resulting solution will now be acidic as there are more protons in the water this reaction is known as hydrolysis - the water causes the substance to split up Stronger bases (e.g. CO3 2- , NH3 and OH¯ ) can remove further protons...
  • 9. HYDROLYSIS -HYDROLYSIS - EQUATIONSEQUATIONS M3+ ions [M(H2O)6]3+ (aq) + H2O(l) [M(H2O)5(OH)]2+ (aq) + H3O+ (aq) the resulting solution will also be acidic as there are more protons in the water this SOLUTION IS MORE ACIDIC due to the greater charge density of 3+ ions Stronger bases (e.g. CO3 2- , NH3 and OH¯ ) can remove further protons...
  • 10. HYDROLYSIS OF HEXAAQUA IONSHYDROLYSIS OF HEXAAQUA IONS Lewis bases can attack the co-ordinated water molecules. Theoretically, a proton can be removed from each water molecule turning the water from a neutral molecule to a negatively charged hydroxide ion. This affects the overall charge on the complex ion. [M(H2O)6]2+ (aq) [M(OH)(H2O)5]+ (aq) [M(OH)2(H2O)4](s) [M(OH)2(H2O)4](s) [M(OH)3(H2O)3]¯(aq) [M(OH)4(H2O)2]2- (aq) [M(OH)4(H2O)2]2- (aq) [M(OH)5(H2O)]3- (aq) [M(OH)6]4- (aq) When sufficient protons have been removed the complex becomes neutral and precipitation of a hydroxide or carbonate occurs. e.g. M2+ ions [M(H2O)4(OH)2](s) or M(OH)2 M3+ ions [M(H2O)3(OH)3](s) or M(OH)3 OH¯ H+ OH¯ H+ OH¯ H+ OH¯ H+ OH¯ H+ OH¯ H+
  • 11. HYDROLYSIS OF HEXAAQUA IONSHYDROLYSIS OF HEXAAQUA IONS Lewis bases can attack the co-ordinated water molecules. Theoretically, a proton can be removed from each water molecule turning the water from a neutral molecule to a negatively charged hydroxide ion. This affects the overall charge on the complex ion. [M(H2O)6]2+ (aq) [M(OH)(H2O)5]+ (aq) [M(OH)2(H2O)4](s) [M(OH)2(H2O)4](s) [M(OH)3(H2O)3]¯(aq) [M(OH)4(H2O)2]2- (aq) [M(OH)4(H2O)2]2- (aq) [M(OH)5(H2O)]3- (aq) [M(OH)6]4- (aq) When sufficient protons have been removed the complex becomes neutral and precipitation of a hydroxide or carbonate occurs. e.g. M2+ ions [M(H2O)4(OH)2](s) or M(OH)2 M3+ ions [M(H2O)3(OH)3](s) or M(OH)3 OH¯ H+ OH¯ H+ OH¯ H+ OH¯ H+ OH¯ H+ OH¯ H+
  • 12. HYDROLYSIS OF HEXAAQUA IONSHYDROLYSIS OF HEXAAQUA IONS Lewis bases can attack the co-ordinated water molecules. Theoretically, a proton can be removed from each water molecule turning the water from a neutral molecule to a negatively charged hydroxide ion. This affects the overall charge on the complex ion. [M(H2O)6]2+ (aq) [M(OH)(H2O)5]+ (aq) [M(OH)2(H2O)4](s) [M(OH)2(H2O)4](s) [M(OH)3(H2O)3]¯(aq) [M(OH)4(H2O)2]2- (aq) [M(OH)4(H2O)2]2- (aq) [M(OH)5(H2O)]3- (aq) [M(OH)6]4- (aq) In some cases, if the base is strong, further protons are removed and the precipitate dissolves as soluble anionic complexes such as [M(OH)6]3- are formed. Very weak bases H2O remove few protons Weak bases NH3, CO3 2- remove protons until precipitation Strong bases OH¯ can remove all the protons OH¯ H+ OH¯ H+ OH¯ H+ OH¯ H+ OH¯ H+ OH¯ H+ Precipitated
  • 13. HYDROLYSIS OF HEXAAQUA IONSHYDROLYSIS OF HEXAAQUA IONS Lewis bases can attack the co-ordinated water molecules. Theoretically, a proton can be removed from each water molecule turning the water from a neutral molecule to a negatively charged hydroxide ion. This affects the overall charge on the complex ion. [M(H2O)6]2+ (aq) [M(OH)(H2O)5]+ (aq) [M(OH)2(H2O)4](s) [M(OH)2(H2O)4](s) [M(OH)3(H2O)3]¯(aq) [M(OH)4(H2O)2]2- (aq) [M(OH)4(H2O)2]2- (aq) [M(OH)5(H2O)]3- (aq) [M(OH)6]4- (aq) In some cases, if the base is strong, further protons are removed and the precipitate dissolves as soluble anionic complexes such as [M(OH)6]3- are formed. Very weak bases H2O remove few protons Weak bases NH3, CO3 2- remove protons until precipitation Strong bases OH¯ can remove all the protons OH¯ H+ OH¯ H+ OH¯ H+ OH¯ H+ OH¯ H+ OH¯ H+ Precipitated
  • 14. HYDROLYSIS OF HEXAAQUA IONSHYDROLYSIS OF HEXAAQUA IONS Lewis bases can attack the co-ordinated water molecules. Theoretically, a proton can be removed from each water molecule turning the water from a neutral molecule to a negatively charged hydroxide ion. This affects the overall charge on the complex ion. [M(H2O)6]2+ (aq) [M(OH)(H2O)5]+ (aq) [M(OH)2(H2O)4](s) [M(OH)2(H2O)4](s) [M(OH)3(H2O)3]¯(aq) [M(OH)4(H2O)2]2- (aq) [M(OH)4(H2O)2]2- (aq) [M(OH)5(H2O)]3- (aq) [M(OH)6]4- (aq) AMPHOTERIC CHARACTER Metal ions of 3+ charge have a high charge density and their hydroxides can dissolve in both acid and alkali. [M(H2O)6]3+ (aq) [M(OH)3(H2O)3](s) [M(OH)6]3- (aq) OH¯ H+ OH¯ H+ OH¯ H+ OH¯ H+ OH¯ H+ OH¯ H+ Precipitated OH¯H+ Insoluble SolubleSoluble
  • 15. STABILITY CONSTANTSSTABILITY CONSTANTS Definition The stability constant, Kstab, of a complex ion is the equilibrium constant for the formation of the complex ion in a solvent from its constituent ions.
  • 16. STABILITY CONSTANTSSTABILITY CONSTANTS Definition The stability constant, Kstab, of a complex ion is the equilibrium constant for the formation of the complex ion in a solvent from its constituent ions. In the reaction [M(H2O)6]2+ (aq) + 6X¯(aq) [MX6]4– (aq) + 6H2O(l)
  • 17. STABILITY CONSTANTSSTABILITY CONSTANTS Definition The stability constant, Kstab, of a complex ion is the equilibrium constant for the formation of the complex ion in a solvent from its constituent ions. In the reaction [M(H2O)6]2+ (aq) + 6X¯(aq) [MX6]4– (aq) + 6H2O(l) the expression for the stability constant is Kstab = [ [MX6 4– ](aq) ] [ [M(H2O)6]2+ (aq) ] [ X¯(aq) ]6
  • 18. STABILITY CONSTANTSSTABILITY CONSTANTS Definition The stability constant, Kstab, of a complex ion is the equilibrium constant for the formation of the complex ion in a solvent from its constituent ions. In the reaction [M(H2O)6]2+ (aq) + 6X¯(aq) [MX6]4– (aq) + 6H2O(l) the expression for the stability constant is Kstab = [ [MX6 4– ](aq) ] [ [M(H2O)6]2+ (aq) ] [ X¯(aq) ]6 The concentration of X¯(aq) appears to the power of 6 because there are six of the ions in the equation. Note that the water isn’t included; it is in such overwhelming quantity that its concentration can be regarded as ‘constant’.
  • 19. STABILITY CONSTANTSSTABILITY CONSTANTS Because ligand exchange involves a series of equilibria, each step in the process has a different stability constant… Kstab / dm3 mol-1 [Co(H2O)6]2+ (aq) + NH3(aq) [Co(NH3)(H2O)5]2+ (aq) + H2O(l) K1 = 1.02 x 10-2 [Co(NH3)(H2O)5]2+ (aq) + NH3(aq) [Co(NH3)2(H2O)4]2+ (aq) + H2O(l) K2 = 3.09 x 10-2 [Co(NH3)2(H2O)4]2+ (aq) + NH3(aq) [Co(NH3)3(H2O)3]2+ (aq) + H2O(l) K3 = 1.17 x 10-1 [Co(NH3)3(H2O)3]2+ (aq) + NH3(aq) [Co(NH3)4(H2O)2]2+ (aq) + H2O(l) K4 = 2.29 x 10-1 [Co(NH3)4(H2O)2]2+ (aq) + NH3(aq) [Co(NH3)5(H2O)]2+ (aq) + H2O(l) K5 = 8.70 x 10-1 etc
  • 20. STABILITY CONSTANTSSTABILITY CONSTANTS Because ligand exchange involves a series of equilibria, each step in the process has a different stability constant… Kstab / dm3 mol-1 [Co(H2O)6]2+ (aq) + NH3(aq) [Co(NH3)(H2O)5]2+ (aq) + H2O(l) K1 = 1.02 x 10-2 [Co(NH3)(H2O)5]2+ (aq) + NH3(aq) [Co(NH3)2(H2O)4]2+ (aq) + H2O(l) K2 = 3.09 x 10-2 [Co(NH3)2(H2O)4]2+ (aq) + NH3(aq) [Co(NH3)3(H2O)3]2+ (aq) + H2O(l) K3 = 1.17 x 10-1 [Co(NH3)3(H2O)3]2+ (aq) + NH3(aq) [Co(NH3)4(H2O)2]2+ (aq) + H2O(l) K4 = 2.29 x 10-1 [Co(NH3)4(H2O)2]2+ (aq) + NH3(aq) [Co(NH3)5(H2O)]2+ (aq) + H2O(l) K5 = 8.70 x 10-1 etc The overall stability constant is simply the equilibrium constant for the total reaction. It is found by multiplying the individual stability constants... k1 x k2 x k3 x k4 ... etc Kstab or pKstab? For an easier comparison, the expression pKstab is often used… pKstab = -log10Kstab
  • 21. STABILITY CONSTANTSSTABILITY CONSTANTS Because ligand exchange involves a series of equilibria, each step in the process has a different stability constant… Kstab / dm3 mol-1 [Co(H2O)6]2+ (aq) + NH3(aq) [Co(NH3)(H2O)5]2+ (aq) + H2O(l) K1 = 1.02 x 10-2 [Co(NH3)(H2O)5]2+ (aq) + NH3(aq) [Co(NH3)2(H2O)4]2+ (aq) + H2O(l) K2 = 3.09 x 10-2 [Co(NH3)2(H2O)4]2+ (aq) + NH3(aq) [Co(NH3)3(H2O)3]2+ (aq) + H2O(l) K3 = 1.17 x 10-1 [Co(NH3)3(H2O)3]2+ (aq) + NH3(aq) [Co(NH3)4(H2O)2]2+ (aq) + H2O(l) K4 = 2.29 x 10-1 [Co(NH3)4(H2O)2]2+ (aq) + NH3(aq) [Co(NH3)5(H2O)]2+ (aq) + H2O(l) K5 = 8.70 x 10-1 etc Summary • The larger the stability constant, the further the reaction lies to the right • Complex ions with large stability constants are more stable • Stability constants are often given as pKstab • Complex ions with smaller pKstab values are more stable
  • 22. REACTION TYPESREACTION TYPES The examples aim to show typical properties of transition metals and their compounds. One typical properties of transition elements is their ability to form complex ions. Complex ions consist of a central metal ion surrounded by co-ordinated ions or molecules known as ligands. This can lead to changes in ... • colour • co-ordination number • shape • stability to oxidation or reduction Reaction types ACID-BASE LIGAND SUBSTITUTION PRECIPITATION REDOX A-B LS OX Ppt RED REDOX
  • 23. REACTION TYPESREACTION TYPES The examples aim to show typical properties of transition metals and their compounds. LOOK FOR... substitution reactions of complex ions variation in oxidation state of transition metals the effect of ligands on co-ordination number and shape increased acidity of M3+ over M2+ due to the increased charge density differences in reactivity of M3+ and M2+ ions with OH¯ and NH3 the reason why M3+ ions don’t form carbonates amphoteric character in some metal hydroxides (Al3+ and Cr3+ ) the effect a ligand has on the stability of a particular oxidation state
  • 24. REACTIONS OF COBALT(II)REACTIONS OF COBALT(II) • aqueous solutions contain the pink, octahedral hexaaquacobalt(II) ion • hexaaqua ions can also be present in solid samples of the hydrated salts • as a 2+ ion, the solutions are weakly acidic but protons can be removed by bases... OH¯ [Co(H2O)6]2+ (aq) + 2OH¯(aq) ——> [Co(OH)2(H2O)4](s) + 2H2O(l) pink, octahedral blue / pink ppt. soluble in XS NaOH ALL hexaaqua ions precipitate a hydroxide with OH¯(aq). Some re-dissolve in excess NaOH A-B
  • 25. REACTIONS OF COBALT(II)REACTIONS OF COBALT(II) NH3 [Co(H2O)6]2+ (aq) + 2NH3(aq) ——> [Co(OH)2(H2O)4](s) + 2NH4 + (aq) ALL hexaaqua ions precipitate a hydroxide with NH3 (aq). It removes protons A-B
  • 26. REACTIONS OF COBALT(II)REACTIONS OF COBALT(II) NH3 [Co(H2O)6]2+ (aq) + 2NH3(aq) ——> [Co(OH)2(H2O)4](s) + 2NH4 + (aq) ALL hexaaqua ions precipitate a hydroxide with NH3 (aq). It removes protons Some hydroxides redissolve in excess NH3(aq) as ammonia substitutes as a ligand. [Co(OH)2(H2O)4](s) + 6NH3(aq) ——> [Co(NH3)6]2+ (aq) + 4H2O(l) + 2OH¯(aq) A-B LS
  • 27. REACTIONS OF COBALT(II)REACTIONS OF COBALT(II) NH3 [Co(H2O)6]2+ (aq) + 2NH3(aq) ——> [Co(OH)2(H2O)4](s) + 2NH4 + (aq) ALL hexaaqua ions precipitate a hydroxide with NH3 (aq). It removes protons Some hydroxides redissolve in excess NH3(aq) as ammonia substitutes as a ligand. [Co(OH)2(H2O)4](s) + 6NH3(aq) ——> [Co(NH3)6]2+ (aq) + 4H2O(l) + 2OH¯(aq) but ... ammonia ligands make the Co(II) state unstable. Air oxidises Co(II) to Co(III) [Co(NH3)6]2+ (aq) ——> [Co(NH3)6]3+ (aq) + e¯ yellow / brown octahedral red / brown octahedral A-B LS OX
  • 28. REACTIONS OF COBALT(II)REACTIONS OF COBALT(II) CO3 2- [Co(H2O)6]2+ (aq) + CO3 2- (aq) ——> CoCO3(s) + 6H2O(l) mauve ppt. Hexaaqua ions of metals with charge 2+ precipitate a carbonate but heaxaaqua ions with a 3+ charge don’t. Ppt
  • 29. REACTIONS OF COBALT(II)REACTIONS OF COBALT(II) CO3 2- [Co(H2O)6]2+ (aq) + CO3 2- (aq) ——> CoCO3(s) + 6H2O(l) mauve ppt. Hexaaqua ions of metals with charge 2+ precipitate a carbonate but heaxaaqua ions with a 3+ charge don’t. Cl¯ [Co(H2O)6]2+ (aq) + 4Cl¯(aq) ——> [CoCl4]2- (aq) + 6H2O(l) pink, octahedral blue, tetrahedral • Cl¯ ligands are larger than H2O • Cl¯ ligands are negatively charged - H2O ligands are neutral • the complex is more stable if tetrahedral - less repulsion between ligands • adding excess water reverses the reaction LS Ppt
  • 30. REACTIONS OF COPPER(II)REACTIONS OF COPPER(II) Aqueous solutions of copper(II) contain the blue, octahedral hexaaquacopper(II) ion Most substitution reactions are similar to cobalt(II). OH¯ [Cu(H2O)6]2+ (aq) + 2OH¯(aq) ——> [Cu(OH)2(H2O)4](s) + 2H2O(l) blue, octahedral pale blue ppt. insoluble in XS NaOH A-B
  • 31. REACTIONS OF COPPER(II)REACTIONS OF COPPER(II) Aqueous solutions of copper(II) contain the blue, octahedral hexaaquacopper(II) ion Most substitution reactions are similar to cobalt(II). OH¯ [Cu(H2O)6]2+ (aq) + 2OH¯(aq) ——> [Cu(OH)2(H2O)4](s) + 2H2O(l) blue, octahedral pale blue ppt. insoluble in XS NaOH NH3 [Cu(H2O)6]2+ (aq) + 2NH3(aq) ——> [Cu(OH)2(H2O)4](s) + 2NH4 + (aq) blue ppt. soluble in excess NH3 then [Cu(OH)2(H2O)4](s) + 4NH3(aq) ——> [Cu(NH3)4(H2O)2]2+ (aq) + 2H2O(l) + 2OH¯(aq) royal blue NOTE THE FORMULA A-B A-B LS
  • 32. REACTIONS OF COPPER(II)REACTIONS OF COPPER(II) Aqueous solutions of copper(II) contain the blue, octahedral hexaaquacopper(II) ion Most substitution reactions are similar to cobalt(II). OH¯ [Cu(H2O)6]2+ (aq) + 2OH¯(aq) ——> [Cu(OH)2(H2O)4](s) + 2H2O(l) blue, octahedral pale blue ppt. insoluble in XS NaOH NH3 [Cu(H2O)6]2+ (aq) + 2NH3(aq) ——> [Cu(OH)2(H2O)4](s) + 2NH4 + (aq) blue ppt. soluble in excess NH3 then [Cu(OH)2(H2O)4](s) + 4NH3(aq) ——> [Cu(NH3)4(H2O)2]2+ (aq) + 2H2O(l) + 2OH¯(aq) royal blue NOTE THE FORMULA CO3 2- [Cu(H2O)6]2+ (aq) + CO3 2- (aq) ——> CuCO3(s) + 6H2O(l) blue ppt. A-B A-B LS Ppt
  • 33. REACTIONS OF COPPER(II)REACTIONS OF COPPER(II) Cl¯ [Cu(H2O)6]2+ (aq) + 4Cl¯(aq) ——> [CuCl4]2- (aq) + 6H2O(l) yellow, tetrahedral • Cl¯ ligands are larger than H2O and are charged • the complex is more stable if the shape changes to tetrahedral • adding excess water reverses the reaction I¯ 2Cu2+ (aq) + 4I¯(aq) ——> 2CuI(s) + I2(aq) off - white ppt. • a redox reaction • used in the volumetric analysis of copper using sodium thiosulphate LS REDOX
  • 34. REACTIONS OF COPPER(I)REACTIONS OF COPPER(I) The aqueous chemistry of copper(I) is unstable compared to copper(0) and copper (II). Cu+ (aq) + e¯ ——> Cu(s) E° = + 0.52 V Cu2+ (aq) + e¯ ——> Cu+ (aq) E° = + 0.15 V subtracting 2Cu+ (aq) ——> Cu(s) + Cu2+ (aq) E° = + 0.37 V This is an example of DISPROPORTIONATION where one species is simultaneously oxidised and reduced to more stable forms. This explains why the aqueous chemistry of copper(I) is very limited. Copper(I) can be stabilised by formation of complexes.
  • 35. REACTIONS OF CHROMIUM(III)REACTIONS OF CHROMIUM(III) Chromium(III) ions are typical of M3+ ions in this block. Aqueous solutions contain the violet, octahedral hexaaquachromium(III) ion. OH¯ [Cr(H2O)6]3+ (aq) + 3OH¯(aq) ——> [Cr(OH)3(H2O)3](s) + 3H2O(l) violet, octahedral green ppt. soluble in XS NaOH As with all hydroxides the precipitate reacts with acid [Cr(OH)3(H2O)3](s) + 3H+ (aq) ——> [Cr(H2O)6]3+ (aq) being a 3+ hydroxide it is AMPHOTERIC as it dissolves in excess alkali [Cr(OH)3(H2O)3](s) + 3OH¯(aq) ——> [Cr(OH)6]3- (aq) + 3H2O(l) green, octahedral A-B A-B A-B
  • 36. REACTIONS OF CHROMIUM(III)REACTIONS OF CHROMIUM(III) CO3 2- 2 [Cr(H2O)6]3+ (aq) + 3CO3 2- (aq) ——> 2[Cr(OH)3(H2O)3](s) + 3H2O(l) + 3CO2(g) The carbonate is not precipitated but the hydroxide is. high charge density of M3+ makes the solution too acidic to form the carbonate CARBON DIOXIDE IS EVOLVED. A-B
  • 37. REACTIONS OF CHROMIUM(III)REACTIONS OF CHROMIUM(III) CO3 2- 2 [Cr(H2O)6]3+ (aq) + 3CO3 2- (aq) ——> 2[Cr(OH)3(H2O)3](s) + 3H2O(l) + 3CO2(g) The carbonate is not precipitated but the hydroxide is. high charge density of M3+ makes the solution too acidic to form the carbonate CARBON DIOXIDE IS EVOLVED. NH3 [Cr(H2O)6]3+ (aq) + 3NH3(aq) ——> [Cr(OH)3(H2O)3](s) + 3NH4 + (aq) green ppt. soluble in XS NH3 With EXCESS AMMONIA, the precipitate redissolves [Cr(OH)3(H2O)3](s) + 6NH3(aq) ——> [Cr(NH3)6]3+ (aq) + 3H2O(l) + 3OH¯(aq) LS A-B A-B
  • 38. REACTIONS OF CHROMIUM(III)REACTIONS OF CHROMIUM(III) Oxidation In the presence of alkali, Cr(III) is unstable and can be oxidised to Cr(VI) 2Cr3+ (aq) + 3H2O2(l) + 10OH¯(aq) ——> 2CrO4 2- (aq) + 8H2O(l) green yellow Acidification of the yellow chromate will produce the orange dichromate(VI) ion Reduction Chromium(III) can be reduced to the less stable chromium(II) by zinc in acid 2 [Cr(H2O)6]3+ (aq) + Zn(s) ——> 2 [Cr(H2O)6]2+ (aq) + Zn2+ (aq) green blue OX RED
  • 39. REACTIONS OF CHROMIUM(VI)REACTIONS OF CHROMIUM(VI) Occurrence dichromate (VI) Cr2O7 2- orange chromate (VI) CrO4 2- yellow Interconversion dichromate is stable in acid solution chromate is stable in alkaline solution in alkali Cr2O7 2- (aq) + 2OH¯(aq) 2CrO4 2- (aq) + H2O(l) in acid 2CrO4 2- (aq) + 2H+ (aq) Cr2O7 2- (aq) + H2O(l)
  • 40. CONTENTSCONTENTS OXIDATION REACTIONS OF CHROMIUM(VI)OXIDATION REACTIONS OF CHROMIUM(VI) Being in the highest oxidation state (+6), chromium(VI) will be an oxidising agent. In acidic solution, dichromate is widely used in both organic (oxidation of alcohols) and inorganic chemistry. It can also be used as a volumetric reagent but with special indicators as its colour change (orange to green) makes the end point hard to observe. Cr2O7 2- (aq) + 14H+ (aq) + 6e¯ ——> 2Cr3+ (aq) + 7H2O(l) [ E° = +1.33 V ] orange green • Its E° value is lower than that of Cl2 (1.36V) so can be used in the presence of Cl¯ ions • MnO4¯ (E° = 1.52V) oxidises chloride in HCl so must be acidified with sulphuric acid • chromium(VI) can be reduced back to chromium(III) using zinc in acid solution
  • 41. REACTIONS OF MANGANESE(VII)REACTIONS OF MANGANESE(VII) • in its highest oxidation state therefore Mn(VII) will be an oxidising agent • occurs in the purple, tetraoxomanganate(VII) (permanganate) ion (MnO4¯) • acts as an oxidising agent in acidic or alkaline solution acidic MnO4¯(aq) + 8H+ (aq) + 5e¯ ——> Mn2+ (aq) + 4H2O(l) E° = + 1.52 V N.B. Acidify with dilute H2SO4 NOT dilute HCl alkaline MnO4¯(aq) + 2H2O(l) + 3e¯ ——> MnO2(s) + 4OH¯(aq) E° = + 0.59 V
  • 42. VOLUMETRIC USE OF MANGANATE(VII)VOLUMETRIC USE OF MANGANATE(VII) Potassium manganate(VII) in acidic (H2SO4) solution is extremely useful for carrying out redox volumetric analysis. MnO4¯(aq) + 8H+ (aq) + 5e¯ ——> Mn2+ (aq) + 4H2O(l) E° = + 1.52 V It must be acidified with dilute sulphuric acid as MnO4¯ is powerful enough to oxidise the chloride ions in hydrochloric acid. It is used to estimate iron(II), hydrogen peroxide, ethanedioic (oxalic) acid and ethanedioate (oxalate) ions. The last two titrations are carried out above 60°C due to the slow rate of reaction. No indicator is required; the end point being the first sign of a permanent pale pink colour. Iron(II) MnO4¯(aq) + 8H+ (aq) + 5Fe2+ (aq) ——> Mn2+ (aq) + 5Fe3+ (aq) + 4H2O(l) this means that moles of Fe2+ = 5 moles of MnO4¯ 1
  • 43. REACTIONS OF IRON(II)REACTIONS OF IRON(II) When iron reacts with acids it gives rise to iron(II) (ferrous) salts. Aqueous solutions of such salts contain the pale green, octahedral hexaaquairon(II) ion OH¯ [Fe(H2O)6]2+ (aq) + 2OH¯(aq) ——> [Fe(OH)2(H2O)4](s) + 2H2O(l) pale green dirty green ppt. it only re-dissolves in very conc. OH¯ but... it slowly turns a rusty brown colour due to oxidation by air to iron(III) increasing the pH renders iron(II) unstable. Fe(OH)2(s) + OH¯(aq) ——> Fe(OH)3(s) + e¯ dirty green rusty brown NH3 Iron(II) hydroxide precipitated, insoluble in excess ammonia CO3 2- Off-white coloured iron(II) carbonate, FeCO3, precipitated A-B A-B OX Ppt
  • 44. CONTENTSCONTENTS REACTIONS OF IRON(II)REACTIONS OF IRON(II) Volumetric Iron(II) can be analysed by titration with potassium manganate(VII) in acidic (H2SO4) solution. No indicator is required. MnO4¯(aq) + 8H+ (aq) + 5Fe2+ (aq) ——> Mn2+ (aq) + 5Fe3+ (aq) + 4H2O(l) this means that moles of Fe2+ = 5 moles of MnO4¯ 1
  • 45. REACTIONS OF IRON(III)REACTIONS OF IRON(III) Aqueous solutions contain the yellow-green, octahedral hexaaquairon(III) ion OH¯ [Fe(H2O)6]3+ (aq) + 3OH¯(aq) ——> [Fe(OH)3(H2O)3](s) + 3H2O(l) yellow rusty-brown ppt. insoluble in XS A-B
  • 46. REACTIONS OF IRON(III)REACTIONS OF IRON(III) Aqueous solutions contain the yellow-green, octahedral hexaaquairon(III) ion OH¯ [Fe(H2O)6]3+ (aq) + 3OH¯(aq) ——> [Fe(OH)3(H2O)3](s) + 3H2O(l) yellow rusty-brown ppt. insoluble in XS CO3 2- 2[Fe(H2O)6]3+ (aq) + 3CO3 2- (aq) ——> 2[Fe(OH)3(H2O)3](s) + 3H2O(l) + 3CO2(g) rusty-brown ppt. The carbonate is not precipitated but the hydroxide is; the high charge density of M3+ makes the solution too acidic to form a carbonate CARBON DIOXIDE EVOLVED. A-B A-B
  • 47. REACTIONS OF IRON(III)REACTIONS OF IRON(III) Aqueous solutions contain the yellow-green, octahedral hexaaquairon(III) ion OH¯ [Fe(H2O)6]3+ (aq) + 3OH¯(aq) ——> [Fe(OH)3(H2O)3](s) + 3H2O(l) yellow rusty-brown ppt. insoluble in XS CO3 2- 2[Fe(H2O)6]3+ (aq) + 3CO3 2- (aq) ——> 2[Fe(OH)3(H2O)3](s) + 3H2O(l) + 3CO2(g) rusty-brown ppt. The carbonate is not precipitated but the hydroxide is; the high charge density of M3+ makes the solution too acidic to form a carbonate CARBON DIOXIDE EVOLVED. NH3 [Fe(H2O)6]3+ (aq) + 3NH3(aq) ——> [Fe(OH)3(H2O)3](s) + 3NH4 + (aq) rusty-brown ppt. insoluble in XS A-B A-B A-B
  • 48. REACTIONS OF IRON(III)REACTIONS OF IRON(III) Aqueous solutions contain the yellow-green, octahedral hexaaquairon(III) ion OH¯ [Fe(H2O)6]3+ (aq) + 3OH¯(aq) ——> [Fe(OH)3(H2O)3](s) + 3H2O(l) yellow rusty-brown ppt. insoluble in XS CO3 2- 2[Fe(H2O)6]3+ (aq) + 3CO3 2- (aq) ——> 2[Fe(OH)3(H2O)3](s) + 3H2O(l) + 3CO2(g) rusty-brown ppt. The carbonate is not precipitated but the hydroxide is; the high charge density of M3+ makes the solution too acidic to form a carbonate CARBON DIOXIDE EVOLVED. NH3 [Fe(H2O)6]3+ (aq) + 3NH3(aq) ——> [Fe(OH)3(H2O)3](s) + 3NH4 + (aq) rusty-brown ppt. insoluble in XS SCN¯ [Fe(H2O)6]3+ (aq) + SCN¯(aq) ——> [Fe(SCN)(H2O)5]2+ (aq) + H2O(l) blood-red colour Very sensitive; BLOOD RED COLOUR confirms Fe(III). No reaction with Fe(II) A-B A-B LS A-B
  • 49. REACTIONS OF SILVER(I)REACTIONS OF SILVER(I) • aqueous solutions contains the colourless, linear, diammine silver(I) ion • formed when silver halides dissolve in ammonia eg AgCl(s) + 2NH3(aq) ——> [Ag(NH3)2]+ (aq) + Cl¯(aq) [Ag(SO3)2]3- Formed when silver salts are dissolved in sodium thiosulphate "hypo" solution. Important in photographic fixing. Any silver bromide not exposed to light is dissolved away leaving the black image of silver as the negative. AgBr + 2S2O3 2- ——> [Ag(S2O3)2]3- + Br¯ [Ag(CN)2]¯ Formed when silver salts are dissolved in sodium or potassium cyanide the solution used for silver electroplating [Ag(NH3)2]+ Used in Tollen’s reagent (SILVER MIRROR TEST) Tollen’s reagent is used to differentiate between aldehydes and ketones. Aldehydes produce a silver mirror on the inside of the test tube Formed when silver halides dissolve in ammonia - TEST FOR HALIDES
  • 50. REACTIONS OF VANADIUMREACTIONS OF VANADIUM Reduction using zinc in acidic solution shows the various oxidation states of vanadium. Vanadium(V) VO2+ (aq) + 2H+ (aq) + e¯ ——> VO2+ (aq) + H2O(l) yellow blue Vanadium(IV) VO2+ (aq) + 2H+ (aq) + e¯ ——> V3+ (aq) + H2O(l) blue blue/green Vanadium(III) V3+ (aq) + e¯ ——> V2+ (aq) blue/green lavender
  • 51. OXIDATION & REDUCTION -OXIDATION & REDUCTION - A SUMMARYA SUMMARY Oxidation • complex transition metal ions are stable in acid solution • complex ions tend to be less stable in alkaline solution • in alkaline conditions they form neutral hydroxides and/or anionic complexes • it is easier to remove electrons from neutral or negatively charged species • alkaline conditions are usually required e.g. Fe(OH)2(s) + OH¯(aq) ——> Fe(OH)3(s) + e¯ Co(OH)2(s) + OH¯(aq) ——> Co(OH)3(s) + e¯ 2Cr3+ (aq) + 3H2O2(l) + 10OH¯(aq) ——> 2CrO4 2- (aq) + 8H2O(l) • Solutions of cobalt(II) can be oxidised by air under ammoniacal conditions [Co(NH3)6]2+ (aq) ——> [Co(NH3)6]3+ (aq) + e¯
  • 52. OXIDATION & REDUCTION -OXIDATION & REDUCTION - A SUMMARYA SUMMARY Oxidation • complex transition metal ions are stable in acid solution • complex ions tend to be less stable in alkaline solution • in alkaline conditions they form neutral hydroxides and/or anionic complexes • it is easier to remove electrons from neutral or negatively charged species • alkaline conditions are usually required e.g. Fe(OH)2(s) + OH¯(aq) ——> Fe(OH)3(s) + e¯ Co(OH)2(s) + OH¯(aq) ——> Co(OH)3(s) + e¯ 2Cr3+ (aq) + 3H2O2(l) + 10OH¯(aq) ——> 2CrO4 2- (aq) + 8H2O(l) • Solutions of cobalt(II) can be oxidised by air under ammoniacal conditions [Co(NH3)6]2+ (aq) ——> [Co(NH3)6]3+ (aq) + e¯ Reduction • Zinc metal is used to reduce transition metal ions to lower oxidation states • It acts in acid solution as follows... Zn(s) ——> Zn2+ (aq) + 2e¯ e.g. it reduces iron(III) to iron(II) vanadium(V) to vanadium (IV) to vanadium(III)
  • 53. REACTIONS OF ALUMINIUMREACTIONS OF ALUMINIUM • aluminium is not a transition metal as it doesn’t make use of d orbitals • BUT, due to a high charge density, aluminium ions behave as typical M3+ ions • aqueous solutions contain the colourless, octahedral hexaaquaaluminium(III) ion OH¯ [Al(H2O)6]3+ (aq) + 3OH¯(aq) ——> [Al(OH)3(H2O3](s) + 3H2O(l) colourless, octahedral white ppt. soluble in XS NaOH As with all hydroxides the precipitate reacts with acid [Al(OH)3(H2O)3](s) + 3H+ (aq) ——> [Al(H2O)6]3+ (aq) being a 3+ hydroxide it is AMPHOTERIC and dissolves in excess alkali [Al(OH)3(H2O)3](s) + 3OH¯(aq) ——> [Al(OH)6]3- (aq) + 3H2O(l) colourless, octahedral CO3 2- 2 [Al(H2O)6]3+ (aq) + 3CO3 2- (aq) ——> 2[Al(OH)3(H2O)3](s) + 3H2O(l) + 3CO2(g) As with 3+ ions, the carbonate is not precipitated but the hydroxide is. NH3 [Al(H2O)6]3+ (aq) + 3NH3(aq) ——> [Al(OH)3(H2O)3](s) + 3NH4 + (aq) white ppt. insoluble in XS NH3 A-B A-B A-B A-B A-B
  • 54. © 2009 JONATHAN HOPTON & KNOCKHARDY PUBLISHING© 2009 JONATHAN HOPTON & KNOCKHARDY PUBLISHING THETHE ENDEND AN INTRODUCTION TOAN INTRODUCTION TO TRANSITION METALTRANSITION METAL COMPLEXESCOMPLEXES