Transition Elements (OCR A Level Chemistry)

This question is about the transition metal copper.

The chloride ion is a monodentate ligand. When concentrated hydrochloric acid is added to [Cu(H₂O)₆]²⁺(aq) ions the water ligands are replaced.

[Co(NH₃)₄Cl₂]⁺ is an example of an octahedral complex which exhibits cis-trans
isomerism.

Bidentate ligands form two coordinate bonds to a central metal atom or ion in a complex.  1,2-diaminoethane is an example of a compound which is a bidentate ligand. 

When added to [Cu(H₂O)₆]²⁺ all of the other ligands are replaced and two optical isomers are formed.

12.2 g of hydrated iron(II) sulfate, FeSO₄.xH₂O were dissolved in acidic solution and made up to a volume of 500 cm³.  A 25.0 cm³ sample of this solution was titrated against 0.0200 mol dm^-3 potassium manganate(VII) solution.  21.95 cm³ of this solution were required.

Complexes of [Pt(NH₃)₂Cl₂] and [Ni(H₂NCH₂CH₂NH₂)₃]²⁺ exhibit different forms of stereoisomerism.

Vanadium (V) oxide is the catalyst used in the contact process as shown by the reactions:

When iron(II) compounds dissolve in water they form [Fe(H₂O)₆]²⁺, the hexaaquairon(II) complex.

Ligand and coordination number are common terms related to transition metals and their complexes.

The complex [Ni(H₂O)₆]²⁺ reacts with 1,2-diaminoethane according to the equation:

[Ni(H₂O)₆]²⁺ + 3H₂NCH₂CH₂NH₂ → [Ni(H₂NCH₂CH₂NH₂)₃]²⁺ + 6H₂O

State and explain the change in coordination number during this reaction.

People with anaemia are often advised to take iron tablets which contain hydrated iron(II) sulfate, FeSO₄.6H₂O.  The composition of these tablets can be analysed by titration with acidified potassium manganate(VII) solution.  

6 g of tablets were crushed, dissolved in deionised water and made up to a volume of 250 cm³ in a volumetric flask. 25.0 cm³ samples of the iron tablet solution were titrated with 0.0200 mol dm^-3 potassium manganate(VII) solution and the average titre value was 22.4 cm³.

Use this information to calculate the percentage of FeSO₄.6H₂O in the tablets.

In humans, oxygen from the lungs dissolves in the blood and enters red blood cells where it forms a complex with haemoglobin.  A molecule of haemoglobin consists of four subunits, each containing an iron-haem complex, as shown below.

Describe the reactions of aqueous copper(II) ions with:

• aqueous sodium hydroxide
• excess aqueous ammonia
• hydrochloric acid.

In your answer you should link observations with equations

Hydrogen peroxide, H₂O₂, is used as an oxidising agent in the oxidation of Cr(OH)₆^3- to form CrO₄^2-.

CrO₄^2- is formed from Cr³⁺ ions.

The half equations for the redox reaction between H₂O₂ and Cr(OH)₆^3- are:

Tollens’ reagent is used to distinguish between aldehydes and ketones.  It can also be referred to as the diamminesilver(I) complex.

Reactions of aqueous copper ions are shown in Figure.

Use Figure of part (a) to answer the following questions: 

A sample of iron(III) chloride is dissolved in water and a pale yellow solution is formed.

Ferric oxalate, also known as iron(III) oxalate, is a chemical compound composed of ferric ions and oxalate ligands. The anhydrous material is pale yellow; however, it may be hydrated to form several hydrates.  Oxalate ions can also be termed ethanedioate ions, C₂O₄^2-, and are bidentate ligands.

This question is about transition metals and transition metal complexes. 

When chromium(III) sulfate dissolves in water, a violet solution forms.

Explain the initial reaction in terms of Brønsted–Lowry Acids & Base Theory.

Compound I is a complex with the empirical formula CoN₄H₁₂Cl₃.

The formula of compound I contains one chloride ion and a complex ion J, which has two stereoisomers.

Draw and label the three-dimensional structures of the two stereoisomers of complex ion J. Include the charge of the complex ion in your diagrams.

Chromium (III) picolinate, shown in Figure 2, is a neutral complex that can be prepared from the weak acid, picolinic acid.

Figure 2

Chromium(III) picolinate is used in tablets as a nutritional supplement for chromium. 

By considering the relevant half equations, write balanced equations for the following chemical reaction.

Acidified potassium manganate(VI) reacting with a lemon-yellow solution of iron ethanedioate, FeC₂O₄ to produce a pale green solution and bubbles of carbon dioxide.

This question is about chromium and cobalt complexes.

Chromium is in the d-block of the Periodic Table.

Hydrated chromium(II) ions react with ethanedioate ions, C₂O₄^2-, to form geometric isomers.

A complex of cobalt has the following composition by mass:

Co, 22.15%; N, 31.28%; H, 6.79%; Cl, 39.78%

State and draw the number of stereoisomers that [Co(H₂NCH₂CH₂NH₂)₂Cl₂]⁺ can form.

This question is about tests for transition metals and catalytic complexes.

Fe²⁺ ions can be used to test for NO₃⁻.

In this test, aqueous iron(II) sulfate is added to a solution containing NO₃⁻ ions, followed by the slow addition of concentrated sulfuric acid. The sulfuric acid forms a layer below the aqueous solution.

In the presence of NO₃⁻ ions, a brown ring forms between the two layers.

Two reactions take place.

Phosphine, PH₃, has a similar structure to ammonia.

Explain how phosphine can act as a ligand.

Levulinic acid is a chemical used to make pharmaceuticals which can be made from renewable resources. The hydrogenation of levulinic acid offers a green and sustainable route to a variety of chemicals used in perfumes. A catalyst for this hydrogenation is dihydridocarbonyltris(triphenylphosphine)ruthenium(Z), [RuH₂(CO)(PPh₃)₃], where Z is the oxidation state of ruthenium. PPh₃ is a common abbreviation for P(C₆H₅)₃ which has a similar structure to phosphine.

Draw the stereoisomers of the catalyst [RuH₂(CO)(PPh₃)₃] and determine whether each stereoisomer has an enantiomer.

Reinecke’s salt is formed by gradually adding ammonium dichromate(VI) to molten ammonium thiocyanate.

Reinecke’s salt has the formula NH₄[Cr(SCN)_x(NH₃)_y] and the following composition by mass: 

Calculate the values of x and y in the above formula. 

Calculate the oxidation number of chromium in the complex.

Suggest a shape for the complex anion.

Draw two possible structures for the anion and state the type of isomerism it exhibits.

Carboplatin and oxaliplatin are both platinum(II) diamines, similar to cisplatin, which are widely used in chemotherapy to treat a wide variety of cancers. However, their use is often plagued with severe toxicity and the development of resistance, which leads to disease progression. Recently, oxoplatin, iproplatin, ormaplatin and satraplatin are Pt complexes that have been used clinically or in clinical trials. 

The four complexes, as shown in Figure 1 below, all have the same geometry and oxidation number for the Pt central atom

Write the oxidation state of Pt and the geometry of the complexes.

Oxaplatin is an isomer of [Pt(NH₃)₂Cl₂(OH)₂] complex. Draw all stereoisomers and indicate the chiral one(s).

Platinum complexes can be considered prodrugs that are intracellularly activated to kill cancer cells.

Cis- platin can be produced by the reduction of the prodrug cis, trans, cis-[PtCl₂(OCOCH₃)₂(NH₃)₂], which has a similar structure to satraplatin.

Draw the structure of cis, trans, cis-[PtCl₂(OCOCH₃)₂(NH₃)₂].