Transition Element Complexes: Isomers, Reactions & Stability (A Level Only) (CIE A Level Chemistry)

Sketch the shape of a 3d_xy orbital.

[2]

Catalysis can be classified as heterogeneous or homogeneous.
Complete Table 7.1 by placing one tick () in each row to indicate the type of catalysis in each reaction.

Table 7.1

[1]

A solution containing a mixture of Sn²⁺(aq) and Sn⁴⁺(aq) is added to a solution containing a mixture of Fe²⁺(aq) and Fe³⁺(aq).

Table 7.2 lists electrode potentials for some electrode reactions of these ions.

Table 7.2

E^ɵ data from the table can be used to predict the reaction that takes place when the two solutions are mixed.

 [1]

Calculate  for this reaction.

[1]

Hexaaquairon(III) ions are pale violet. They form a colourless complex with fluoride ions, F^–, as shown in equilibrium 1, and a deep-red complex with thiocyanate ions, SCN^–, as shown in equilibrium 2.

                           violet                                deep-red

The following two experiments are carried out.

Experiment 1: A few drops of KSCN(aq) are added to 5 cm³ of Fe³⁺(aq), followed by a few drops of KF(aq).

Experiment 2: A few drops of KF(aq) are added to 5 cm³ of Fe³⁺(aq), followed by a few drops of KSCN(aq).

   [4]

[1]

Solutions of iron(III) salts are acidic due to the equilibrium shown.

Calculate the pH of a 0.25 mol dm^–3 FeCl₃ solution.
Show your working.

pH = ..........................................................

This question is about transition metal complexes.

An aqueous solution of copper(II) contains the [Cu(H₂O)₆]²⁺ complex ion.

Define the term complex ion.

A sample of [Cu(H₂O)₆]²⁺ is reacted with aqueous sodium hydroxide and a separate sample of [Co(H₂O)₆]²⁺ with an excess of aqueous ammonia.

Give the following information about these reactions.

• the reaction of [Cu(H₂O)₆]²⁺ with aqueous sodium hydroxide
   
  colour and state of the copper-containing species
  
  .......................................................................................................
   
  ionic equation ................................................................................
   
  type of reaction ..............................................................................
  
  
• the reaction of [Co(H₂O)₆]²⁺ with an excess of aqueous ammonia
   
  colour and state of the cobalt-containing species
  
  .......................................................................................................
   
  ionic equation ................................................................................
   
  type of reaction ..............................................................................

The [Fe(NH₃)₂CN₄]^– complex shows stereoisomerism.

Complete the three-dimensional diagrams to show the two isomers of  [Fe(NH₃)₂CN₄]^–.

Suggest the type of stereoisomers.

Compound A, C₄H₁₃N₃, is a tridentate ligand. 

Cobalt is a transition element with atomic number 27.

Complete the electronic configurations of a Co atom and a Co²⁺ ion.

Co²⁺ ions form a linear complex with Cl^– ions, which are monodentate ligands.

Draw the structure of this complex and include its overall charge.

structure

charge ......................................

Co²⁺ ions exist as [Co(H₂O)₆]²⁺ complex ions in an aqueous solution.

Complete a three-dimensional diagram to show the shape of this complex.

Name its shape.

Label and state the value of two bond angles.

When NH₃ (aq) is added to Co²⁺ (aq), dropwise at first and then in excess, two chemical reactions occur as shown.

[Co(H₂O)₆]²⁺  A  B

For each reaction, describe what you would see and write an equation.

EDTA^4– is a hexadentate ligand. When a solution of EDTA^4– is added to a solution containing [Co(H₂O)₆]²⁺ a new complex is formed. The formula of this complex is [CoEDTA]^2–.

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

Explain the origin of colour in a transition element complex such as [Co(NH₃)₄Cl₂]⁺.

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.

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. 

Fig. 1.1

Give the following information for the complexes.

oxidation number of the platinum ion ..................................................

shape of the complexes ..................................................

One isomer of the [Pt(NH₃)₂Cl₂(OH)₂] complex oxoplatin is shown in part (a) Fig. 1.1.

Complete three-dimensional diagrams to show the shape of the other oxoplatin 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].

When chromium(III) sulfate dissolves in water, a green solution containing the [Cr(H₂O)₆]³⁺ ion forms.

Ethylenediaminetetraacetate, EDTA⁴⁻, shown in Fig. 2.1. is a polydentate ligand.

Fig. 2.1

When a solution of EDTA⁴⁻ is added to a solution of [Cr(H₂O)₆]³⁺ ions, a new complex ion is formed.

[Cr(H₂O)₆]³⁺ + EDTA^4– ⇌ [Cr(EDTA)]^– + 6H₂O

Compound L is a complex with the empirical formula CrN₄H₁₂Cl₃ 

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

Complete three-dimensional diagrams to show the shape of the stereoisomers of complex ion M.

Chromium (III) picolinate, shown in Fig. 2.2, is a neutral complex that can be prepared from the weak acid, picolinic acid.

Fig. 2.2

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

Iron(II) gluconate, C₁₂H₂₂FeO₁₄, is the active ingredient in some brands of iron supplements.

A student carries out an experiment to determine the mass of iron(II) gluconate in one tablet of an iron supplement, using the method below.

1. The student crushes two tablets and dissolves the powdered tablets in dilute sulfuric acid
2. The student makes up the solution from step 1 to 250.0 cm³ in a volumetric flask.
3. The student then titrated 25.0 cm³ portions of the solution obtained in step 2 with 0.00200 mol dm⁻³ potassium manganate(VII).

The student obtains a mean titre of 13.50 cm³.

In this titration, 1 mole of manganate(VII) ions reacts with 5 moles of iron(II) ions.

Determine the mass, in mg, of iron(II) gluconate in one tablet. Give your answer to 3 significant figures.

The typical concentration of a potassium manganate(VII) solution used in redox titrations is 0.0200 mol dm^-3.

Use the information in part (a) to explain, quantitatively, why the student replaced this with a 0.00200 mol dm^-3 potassium manganate(VII) solution for this titration.

Some iron supplements contain iron(II) sulfate or iron(II) fumarate.

Table 3.1 shows the information taken from the labels of two iron supplements, A and B.

Table 3.1

State which iron supplement, A or B, would provide the greater mass of iron per tablet. Show your workings.

Write an equation for the reaction between ethanedioic acid, H₂C₂O₄, and sodium hydroxide, NaOH.

15.00 cm³ of H₂C₂O₄ (aq) requires 10.30 cm³ of a 0.25 mol dm^-3 solution of NaOH for complete neutralisation using a phenolphthalein indicator for the first permanent colour change. 

15.00 cm³ of the same H₂C₂O₄ (aq) required 12.35 cm³ of potassium permanganate, KMnO₄, solution for complete oxidation to carbon dioxide and water in the presence of dilute sulfuric acid to further acidify the H₂C₂O₄ (aq) for the first permanent
colour change. 

Calculate the moles of H₂C₂O₄ (aq) therefore the concentration of the solution.

Write the full redox equation, including state symbols, for this redox titration.

Calculate the concentration of the potassium permanganate, KMnO₄, solution.