Transition Elements (OCR A Level Chemistry A): Flashcards

The coordination number is the total number of coordinate (dative) bonds formed between the central metal atom or ion and its ligands.

A monodentate ligand forms one dative bond to a central metal ion, whereas a bidentate ligand forms two dative bonds.

False.

1,2-diaminoethane is a bidentate ligand because each molecule contains two nitrogen atoms with lone pairs, allowing it to form two dative bonds.

Chloride ions are large ligands, so only four will fit around the central metal ion, and their size favours the tetrahedral arrangement with bond angles of 109.5^o.

True.

Cisplatin has four coordinate bonds arranged in a square planar geometry, with bond angles of 90^o.

Octahedral complexes have bond angles of 90^o and tetrahedral complexes have bond angles of 109.5^o.

Geometric isomers are stereoisomers that differ in the arrangement of groups around a restricted bond or geometry, existing as cis and trans forms.

The restricted geometry means ligands cannot rotate freely, so complexes with two pairs of different ligands can exist with those ligands adjacent (cis) or opposite (trans) to each other.

Optical isomers are non-superimposable mirror images that cannot be superimposed on each other and differ only in the direction they rotate plane-polarised light.

True.

Such complexes have no plane of symmetry, so the two mirror-image forms are non-superimposable and therefore optical isomers.

Cisplatin undergoes ligand exchange inside the cell, replacing its chloride ligands with water, then binds to nitrogen atoms on DNA bases, distorting the DNA and preventing replication.

False.

Only cisplatin has the correct geometry to bind to DNA and inhibit replication; trans-platin cannot be used in cancer treatment.

Cisplatin binds to healthy cells as well as cancer cells, and hair follicle cells replicate rapidly, making them particularly vulnerable to the DNA-distorting action of the drug.

Ligand substitution (ligand exchange) is the process in which one or more ligands in a complex are replaced by other ligands to form a new, more stable complex.

Excess NH₃ causes partial ligand substitution, replacing four water and hydroxide ligands to form [Cu(NH₃)₄(H₂O)₂]²⁺, which absorbs different wavelengths and appears deep blue.

Adding concentrated HCl to [Cu(H₂O)₆]²⁺ replaces all water ligands with four chloride ligands, changing the geometry from octahedral to tetrahedral.

True.

Chloride ions are larger than water molecules, so only four fit around the central Cu²⁺ ion, reducing the coordination number from 6 to 4.

The dark green precipitate dissolves to form a dark green solution of [Cr(OH)₆]^3- (aq) as the remaining water ligands are replaced by hydroxide ligands.

A hexaaqua complex ion is a transition metal ion surrounded by six water ligands, for example [Cu(H₂O)₆]²⁺, which is the form in which transition metal ions exist in aqueous solution.

Larger ligands take up more space around the central metal ion, so fewer can fit, reducing the coordination number and changing the geometry of the complex.

False.

Fe³⁺ (aq) reacts with NaOH (aq) to form an orange-brown precipitate of Fe(H₂O)₃(OH)₃ (s), not dark green.

Haemoglobin is a biological complex containing iron(II) at the centre of the haem molecule, responsible for transporting oxygen around the body in the blood.

Oxygen is a weak ligand that forms a weak dative covalent bond with the Fe(II) ion, so the bond breaks easily to deliver oxygen to cells.

Carbon monoxide binds strongly and irreversibly to the iron(II) ion in haemoglobin, preventing oxygen from being carried to cells.

CO is a better ligand than oxygen and binds irreversibly to the Fe(II) in haemoglobin, forming carboxyhaemoglobin and blocking oxygen transport.

False.

Carboxyhaemoglobin is a darker red colour, which can be a visible sign of carbon monoxide poisoning.

Anaemia is a condition where there is insufficient haemoglobin in the blood; iron-deficiency anaemia can be treated by taking iron sulfate tablets in the diet.

In the haem molecule, oxygen forms a dative covalent bond with the Fe(II) ion at its centre.

A disproportionation is a redox reaction in which the same element is simultaneously oxidised and reduced, resulting in two different oxidation states.

The reaction is self-indicating: MnO₄^- is deep purple and is reduced to near-colourless Mn²⁺, so the endpoint is visible when the purple colour persists.

In the reaction of Fe²⁺ with acidified MnO₄^-, iron is oxidised to Fe³⁺ and manganese is reduced to Mn²⁺.

The solution changes from orange (Cr₂O₇^2-) to green (Cr³⁺) and then to pale blue (Cr²⁺) as zinc reduces chromium further.

True.

This is disproportionation: Cu⁺ in Cu₂O is oxidised to Cu²⁺ (in CuSO₄) and reduced to Cu (s) at the same time.

Alkaline conditions provide hydroxide ions (OH^-) that shift the equilibrium, making transition metals in low oxidation states easier to oxidise.

When excess I^- ions react with Cu²⁺, a white precipitate of CuI forms and brown iodine is produced.

The orange-brown Fe³⁺ solution turns pale green as Fe³⁺ is reduced to Fe²⁺, though the colour may be masked by brown iodine also produced.

True.

Acidification converts chromate(VI) (yellow) to dichromate(VI) (orange) via: 2CrO₄^2- (aq) + 2H⁺ (aq) → Cr₂O₇^2- (aq) + H₂O (l).

A qualitative analysis is a set of chemical tests used to identify the ions present in an unknown solution, producing observable results such as colour changes or precipitates.

AgCl dissolves in dilute ammonia, AgBr dissolves in concentrated ammonia, and AgI is insoluble in concentrated ammonia.

NH₄⁺ ions react with OH^- ions when heated to produce ammonia gas, which turns damp red litmus paper blue.

Carrying out tests in the correct order prevents reagents from one test interfering with the results of subsequent tests.

False.

AgI is insoluble in concentrated ammonia, unlike AgCl (soluble in dilute ammonia) and AgBr (soluble in concentrated ammonia).

Coloured hydroxide precipitates form, with each transition metal ion producing a characteristic colour that can be used to identify it.

The ionic equation for the reaction of ammonium ions with hydroxide ions is: NH₄⁺ (aq) + OH^- (aq) → ammonia, NH₃ (g) + water, H₂O (l).