Chapter 24 - Transition Elements Flashcards
What are the physical properties of d block elements?
Typical physical properties of metals - metallic.
High melting points and boiling points, shiny in appearance and conduct electricity and heat
Which 2 d block elements do not follow typical electron configuration patterns?
Copper - 3d10 4s1
Chromium - 3d5 4s1
This is due to stability (half filled d sub shell and fully filled d sub shell gives additional stability to copper and chromium atoms)
What is the rule for orbital filling 3d/4s?
4s ALWAYS fills before the 3d orbitals
However, the 4s orbital will also empty before the 3d orbital
What is a transition element?
D block elements that form at least one ion with a partially filled d orbital
Which 2 d block elements are not classified as transition elements, and why?
Scandium - only forms ion Sc3+ with loss of 2 4s e- and 1 3d e-
Zinc - only forms ion Zn2+ with loss of 2 4s e-
What are the characteristic properties of transition elements which differentiates them from other metals?
- form compounds with different oxidation states
- form coloured compounds
- elements and their compounds can act as catalysts
Why do transition elements form different coloured compounds?
Due to the partially filled d orbitals in the transition metal ion, the colour of a solution varies with different oxidation states
How do transition metals act as catalysts?
- lower activation energy
- provide alternative reaction pathway
- speeding up the rate of reaction
- and are not used up
What are examples of homogeneous and heterogeneous transition metal catalysts?
Homogeneous = sodium thiosulfate titrations, e.g. Fe2+ as an oxidising agent
Heterogeneous = Ni catalyst in hydrogenation
What is a complex ion?
One or more molecules/negatively charged ions bonded to a single metal ion
What is a coordinate bond?
A dative covalent bond in which both electrons in the shared pair come from the same atom
What is a coordination number?
The number of coordinate bonds attached to the central metal ion
What is a ligand?
An ion or molecule with a lone pair, that forms a coordinate bond with a transition metal by donating an electron pair
What is a monodentate ligand, what are some common examples?
A ligand that is able to donate one pair of electrons to a central metal ion
H2O: :NH3 :Cl- :CN- :OH-
What is a bidentate ligand, what are some common examples?
Ligands which can donate two lone pairs of electrons to the central metal ion, forming 2 coordinate bonds
1,2-diaminoethane (en) and ethanedioate ion
Which atoms donate lone pairs in 1,2-diaminoethane (en) and ethanedioate ion?
en = each nitrogen atom donates a pair of electrons to the central metal ion
ethanedioate ion = each negatively charged oxygen atom donates a lone pair of electrons to the central metal ion
What are the types of shapes for complex ions?
Six co-ordinate complexes (octahedral)
Four co-ordinate complexes (tetrahedral, square planar)
What is the bond angle and coordination number for octahedral complex ions?
90 degrees
6
What is the bond angle and coordination number for tetrahedral and square planar complex ions?
Tetrahedral = 109.5 degrees and 4
Square planar = 90 degrees and 4
What types of stereoisomerism can you get in complex ions?
Cis trans isomerism
Optical isomerism
Which types of complex ions does cis trans isomerism occur in?
Some square planar and octahedral complex ions
How are cis and trans isomers arranged in square planar complex ions?
Cis = two identical groups are adjacent to each other (coordinate bonds between 2 ligands 90 degrees apart)
Trans = two identical groups are opposite to each other (coordinate bonds between 2 ligands 180 degrees apart)
How are cis and trans isomers arranged in octahedral complex ions?
Cis = two identical ligands adjacent to each other with their coordinate bonds separated by 90 degrees
Trans = two identical ligands at opposite corners of the octahedron, with coordinate bonds 180 degrees apart
What type of complex ions does optical isomerism occur in?
Only in OCTAHEDRAL complexes containing 2 or more bidentate ligands (CIS ISOMERS)
Trans isomers cannot form optical isomers as a mirror image is exactly the same and can be superimposed
What is a ligand substitution reaction?
A reaction where one ligand in a complex ion is replaced by another ligand
What does copper sulfate form when dissolved in water (what colour complex)?
[Cu(H2O)6] 2+
Pale blue
What happens when excess ammonia is added to a solution containing [Cu(H2O6]2+?
(reaction, colour change, shape change, qualitative analysis)
[Cu(H2O)6]2+ + 4NH3 → [Cu(NH3)4(H2O)2] 2+ + 4H2O
Pale blue solution to dark blue solution
4 ammonia ligands replace 4 water ligands, so octahedral shape remains the same.
QA: pale blue Cu(OH)2 precip forms first, then dissolves in excess ammonia to form dark blue solution
What happens when excess hydrochloric acid is added to a solution containing [Cu(H2O6]2+?
(reaction, colour change, shape change, oxidation number change)
[Cu(H2O)6] 2+ + 4Cl- ⇌ [CuCl4] 2- + 6H2O
Pale blue solution to yellow solution
Six water ligands replaced by 4 larger chloride ligands so change from octahedral to tetrahedral
Copper remains as +2
What does chromium (III) potassium sulfate, KCr(SO4)2.2(H2O) form when dissolved in water? (what colour is the solution?)
Forms [Cr(H2O)6] 3+
Violet solution
What does chromium (III) sulfate, KCr(SO4)2.2(H2O) form when dissolved in water? (what colour is the solution?)
[Cr(H2O)5SO4]+
Green solution
What happens when [Cr(H2O)6] 3+ reacts with excess aqueous ammonia? (reaction, qualitative analysis, colour change)
[Cr(H2O)6]3+ + 6NH3 → [Cr(NH3)6] 3+ + 6H2O
Ligand substitution of all of the H2O for NH3
QA: initially grey-green precip of Cr(OH)3 formed, which then dissolves in excess ammonia
Violet to purple
What is the structure of hameoglobin?
Four protein chains held together by weak intermolecular forces.
Each chain has a haem group where the central metal ion is Fe2+ bonded to ligand O2 gas
What happens when to haemoglobin when blood passes through the lungs?
Haemoglobin binds to oxygen due to increased oxygen pressure forming oxyhaemoglobin. This releases O2 to body cells as and when required.
Haemoglobin in red blood cells also bonds to CO2 which is carried back to lungs, and then released and exhaled.
What happens when carbon monoxide binds to Fe2+ in haemoglobin?
Forms carboxyhaemoglobin due to ligand substitution of oxygen for carbon monoxide.
CO binds more strongly than oxygen (and the bond is so strong the process is irreversible), so a small conc of CO in the lungs prevents large proportion of haemoglobin from carrying oxygen. If carboxyhaemoglobin conc becomes too high, O2 transport is prevented, leading to death.
What is a precipitation reaction?
When two aqueous solutions containing ions react together to form an insoluble ionic solid called a precipitate
Reaction of copper (ii) with NaOH, NH3
(reactions, overall, colour change, precipitate solubility)
NaOH: [Cu(H2O)6]2+ (aq) + 2OH- (aq) → [Cu(OH)2(H2O)4] (s) + 2H2O (l)
NH3: [Cu(H2O)6]2+ (aq) + 2NH3 (aq) → [Cu(OH)2(H2O)4] (s) + 2NH4+ (aq)
Overall: Cu 2+ (aq) + 2OH- (aq) → Cu(OH)2 (s)
Colour: blue solution to blue precipitate
Precipitate insoluble in excess NaOH, but undergoes ligand sub in excess NH3 to form a dark blue solution
Reaction of iron (ii) with NaOH, NH3
(reactions, overall, colour change, precipitate solubility)
NaOH: [Fe(H2O)6]2+ (aq) + 2OH- (aq) → [Fe(OH)2(H2O)4] (s) + 2H2O (l)
NH3: [Fe(H2O)6]2+ (aq) + 2NH3 (aq) → [Fe(OH)2(H2O)4] (s) + 2NH4+ (aq)
Overall: Fe 2+ (aq) + 2OH- (aq) → Fe(OH)2 (s)
Colour change: pale green solution to green precipitate, which changes to brown on standing in air
Precipitate insoluble in excess NaOH/NH3
Why does iron (ii) precipitate change colour in air?
Iron (II) is oxidised to Iron (III)
Fe(OH)2 (s) → Fe(OH)3 (s) which is orange/brown
Reaction of iron (iii) with NaOH, NH3
(reactions, overall, colour change, precipitate solubility)
NaOH: [Fe(H2O)6]3+ (aq) + 3OH- (aq) → [Fe(OH)3(H2O)3] (s) + 3H2O (l)
NH3: [Fe(H2O)6]3+ (aq) + 3NH3 (aq) → [Fe(OH)3(H2O)3] (s) + 3NH4+ (aq)
Overall: Fe 3+ (aq) + 3OH- (aq) → Fe(OH)3 (s)
Colour change: pale yellow solution to orange brown precipitate
Precipitate insoluble in excess NaOH/NH3
Reaction of manganese (ii) with NaOH, NH3
(reactions, overall, colour change, precipitate solubility)
NaOH: [Mn(H2O)6]2+ (aq) + 2OH- (aq) → [Mn(OH)2(H2O)4] (s) + 2H2O (l)
NH3: [Mn(H2O)6]2+ (aq) + 2NH3 (aq) → [Mn(OH)2(H2O)4] (s) + 2NH4+ (aq)
Overall: Mn 2+ (aq) + 2OH- (aq) → Mn(OH)2 (s)
Colour change: pale pink solution to light brown precipitate which darkens on standing in air
Precipitate insoluble in excess NaOH/NH3
Reaction of chromium (iii) with NaOH, NH3
(reactions, overall, colour change)
NaOH: [Cr(H2O)6]3+ (aq) + 3OH- (aq) → [Cr(OH)3(H2O)3] (s) + 3H2O (l)
NH3: [Cr(H2O)6]3+ (aq) + 3NH3 (aq) → [Cr(OH)3(H2O)3] (s) + 3NH4+ (aq)
Overall: Cr 3+ (aq) + 3OH- (aq) → Cr(OH)3 (s)
Colour change: violet solution to grey/green precipitate
What happens when precipitate Cr(OH)3 dissolved in excess NH3? (reaction, overall and colour change)
Soluble in excess NH3
[Cr(OH)3(H2O)3] s + 6NH3 aq → [Cr(NH3)6]3+ aq + 3H2O l + 3OH- aq
Grey green precipitate to purple solution
What happens when precipitate Cr(OH)3 dissolved in excess NaOH? (reaction and colour change)
Soluble in excess NaOH
[Cr(OH)3(H2O)3] s + 3OH- aq → [Cr(OH)6] 3- aq + 3H2O (l)
Grey green precipitate to dark green solution
Which transition metal precipitates are soluble in excess NaOH/NH3?
Cu(OH)2 soluble in ammonia only
Cr(OH)3 soluble in sodium hydroxide and ammonia
What is cisplatin, how does it work?
An isomer used as an anticancer drug
Prevents DNA double helix from unwinding by forming coordinate bonds with DNA bases - removes chlorine ligands and cisplatin binds to guanine. Therefore prevents replication
What are the side effects of cisplatin?
- prevents normal non cancerous cells in the body from replicating
- patients can become resistant
- may experience side effects e.g. nausea or kidney damage
What is the equation and colour change for the redox reaction between Fe 2+ and MnO4- in acid conditions? What is oxidised and what is reduced?
OXIDATION OF Fe2+, REDUCTION OF MnO4-
MnO4- + 8H+ + 5Fe 2+ → Mn 2+ + 5Fe 3+ + 4H2O
Purple to colourless
What is the equation and colour change for the redox reaction between Fe 3+ and I-? What is oxidised and what is reduced?
REDUCTION OF Fe 3+, OXIDATION OF I-
2Fe 3+ + 2I- → 2Fe 2+ + I2
Orange brown Fe 3+ to pale green Fe3+ (but obscured by oxidation of iodide ions which also have a brown colour as iodine)
What is the equation and colour change for the redox reaction between Cr2O7 2- and Zn? What is oxidised and what is reduced?
REDUCTION OF Cr2O7 2-, OXIDATION OF Zn
Cr2O7 2- + 14H+ + 3Zn → 2Cr3+ + 7H2O + 3Zn 2+
Orange to green
What happens when excess zinc is added to Cr 3+ ions?
Chromium (III) ions are reduced further to chromium (II) which is a pale blue colour
(Green to blue)
What is the equation for the redox reaction between H2O2/OH- and Cr3+? What is oxidised, what is reduced?
OXIDATION OF Cr 3+, REDUCTION OF O IN H2O2
3H2O2 + 2Cr3+ +10OH- → 2CrO4 2- + 8H2O
What is the equation and colour change for the redox reaction between Cu2+ and iodide ions? What is oxidised, what is reduced?
REDUCTION OF Cu2+, OXIDATION OF I-
2Cu 2+ + 4I- → 2CuI + I2
Pale blue solution to brown solution with white CuI precipitate
What is the equation for the disproportionation of Cu+ ions when copper (I) oxide reacts with hot dilute sulfuric acid? Where has reduction and oxidation taken place?
Cu2O + H2SO4 → Cu + CuSO4 + H2O
Reduction of Cu2O to Cu
Oxidation of Cu2O to CuSO4
How can you identify transition metal cations?
Aqueous sodium hydroxide producing precipitates
How can you identify ammonium ions?
Heat with hydroxide ions
NH4+ + OH- → NH3 + H2O
Releases ammonia gas which turns damp red pH paper blue
