Shapes of complex ions

Chromium forms the complex ions [Cr(NH₃)₆]³⁺ and [Cr(OH)₆]^3–.

Which statement(s) about the complexes is / are correct?

1 Chromium is in the same oxidation state in each complex ion.

2 The complex ions are different colours.

3 The complex ions have different coordination numbers.

A 1, 2 and 3

B Only 1 and 2

C Only 2 and 3

D Only 1

This question is about reactions of compounds of iron and copper.

Complete the electron configuration of

an Fe atom: 1s²........

a Cu²⁺ ion: 1s²........

Solutions of iron(II) sulfate, FeSO₄, and copper(II) sulfate, CuSO₄, can be distinguished by adding aqueous sodium hydroxide.

Describe what would be observed when NaOH(aq) is added to each solution.

Observation with FeSO₄(aq)........

Observation with CuSO₄(aq)........

The cyclic organic compound pyridine, C₅H₅N, can act as a monodentate ligand.

The structure of pyridine is shown below.

What is meant by a monodentate ligand ?

Aqueous copper(II) sulfate reacts with salicylic acid to form a complex ion which has two stereoisomers.

One isomer of the complex ion is shown:

Draw the other stereoisomer of the complex.

Identify the type of stereoisomerism shown by the complexes.

Type of stereoisomerism........

Calculate the percentage by mass of CuSO₄•5H₂O in Mixture A.

Give your answer to 3 significant figures.

Percentage of CuSO₄•5H₂O in Mixture A =........ %

The student repeats their method, but after carrying out Step 1 they leave the solution exposed to the air for a few days. Some of the iron(II) sulfate is oxidised to iron(III) sulfate.

The student then continues with Step 2, Step 3 and Step 4 of the method.

This mean titre is greater than 31.15 cm³.

Suggest why this mean titre is greater than 31.15 cm³.

This question is about inorganic chemistry.

The flowchart shows reactions involving SO₃^2–(aq) ions.

What is the systematic name of a SO₃^2– ion?

Construct an ionic equation for the reaction of SO₃^2– with H⁺/Cr₂O₇^2–.

The structure of a neutral nickel(II) complex, A, is shown below.

What is the empirical formula of complex A ?

Complete the 3D diagram below to show a stereoisomer of complex A.

This question is about compounds and ions of iron(II) and iron(III) that contain ethanedioate ions, C₂O₄^2–.

The C₂O₄^2– ion, shown below, is an example of a bidentate ligand.

Explain what is meant by the term bidentate ligand.

A complex ion E contains three C₂O₄^2– ions bonded to an iron(III) ion in an octahedral shape.

Complex ion E exists as a mixture of two optical isomers.

Draw 3D diagrams to show the structures of the optical isomers of E.

Include any overall charge.

A student plans an investigation to find the number of waters of crystallisation, x, in a sample of hydrated iron(II) ethanedioate, FeC₂O₄•xH₂O.

The student decides to carry out a redox titration between solutions of iron(II) ethanedioate and potassium manganate(VII) in acidic conditions.

In the titration, both iron(II) ions and ethanedioate, C₂O₄^2–, ions are oxidised.

Construct half-equations for the oxidation of iron(II) and ethanedioate ions.

Oxidation of iron(II) ions

Oxidation of ethanedioate ions

The uncertainty in each burette reading is ±0.05 cm³.

Calculate the percentage uncertainty for the titre in Titration 1.

* In the titration, 5 mol of iron(II) ethanedioate reacts with 3 mol of manganate(VII) ions.

Analyse the student’s results to find the number of waters of crystallisation, x, in the hydrated

iron(II) ethanedioate, FeC₂O₄•xH₂O.

Which statement(s) is/are correct for the anti-cancer complex Pt(NH₃)₂Cl₂?

1 It has bond angles of 90º.

2 The oxidation number of Pt is +4.

3 It forms both optical and cis-trans isomers.

A 1, 2 and 3

B Only 1 and 2

C Only 2 and 3

D Only 1

Your answer

This question is about reactions of transition metal compounds.

Explain why ethane-1,2-diamine can act as a bidentate ligand.

The iron(III) ion, Fe³⁺, forms a complex ion A with two ethane-1,2-diamine ligands and two chloride ligands.

Complex ion A has cis and trans stereoisomers. One of these stereoisomers exists as optical isomers.

Determine the empirical formula, with charge, of complex ion A and draw the 3-D structures of the three stereoisomers.

Empirical formula with charge........

Structures

Aqueous sodium hydroxide is added to an aqueous solution of iron(II) sulfate. A pale green precipitate forms which turns brown when left to stand in air.

Write an ionic equation for the formation of the pale green precipitate.

* This question is about copper and copper compounds.

Experiment 1 Hydrochloric acid, HCl (aq), is added to an aqueous solution containing [Cu(H₂O)₆]²⁺ complex ions. A yellow-green solution forms containing complex ion B.

Experiment 2 A piece of copper metal is heated with concentrated sulfuric acid. A reaction takes place forming a pale blue solution C and 45 cm³ of a gas D, measured at RTP. The mass of gas D is 0.12 g.

Experiment 3 An excess of copper(II) oxide is heated with dilute nitric acid. The resulting mixture is filtered. The filtrate is a blue solution E. Aqueous potassium iodide, K I (aq), is added to the blue solution E. A white precipitate F and a brown solution G form.

Determine the formulae of B – G. Construct equations for the reactions taking place, include any changes in oxidation number,

and show your working where appropriate.

These questions are from different areas of chemistry.

Ammonia, NH₃, and ammonium nitrate, NH₄NO₃, are compounds of nitrogen.

The boiling point of NH₃ is –33 °C.

The boiling point of NH₄NO₃ is 210 °C.

Explain why there is a large difference in boiling points.

Two students discuss the oxidation numbers in ammonium nitrate, NH₄NO₃.

One student claims that the two nitrogen atoms have the same oxidation number. The other student disagrees and claims that the nitrogen atoms have different oxidation numbers.

Explain with reasons which student is correct.

What are the percentage compositions of copper and zinc in the brass sample?

Calculate the relative atomic mass of zinc in the sample of brass.

Give your answer to 2 decimal places.

Fill in the table to predict the splitting patterns in the proton NMR spectrum of the

The table shows the chemical shifts for the peaks in the proton NMR spectrum at proton environments 2 and 3.

Proton environment	2	3
Chemical shift,	2.5 ppm	3.6 ppm

Suggest why the peaks for proton environments 2 and 3 have the chemical shifts which are shown in the table.

Glycine, H₂NCH₂COOH, is an -amino acid.

Glycine reacts with NaOH to form the salt H₂NCH₂COONa.

Glycine reacts with HCl to form the salt HOOCCH₂NH₃Cl.

The salts have different H–N–H bond angles.

State the different H–N–H bond angles and explain why they are different.

H₂NCH₂COONa H–N–H bond angle =........ °

HOOCCH₂NH₃Cl H–N–H bond angle =........ °

Glycine reacts with aqueous copper(II) ethanoate to form copper(II) glycinate, Cu(H₂NCH₂COO)₂, and ethanoic acid. Copper(II) glycinate is a complex which exists as two square planar isomers.

Write an equation for this reaction and draw the structures of the two square planar isomers of the complex Cu(H₂NCH₂COO)₂.

equation

This question is about d-block elements.

Most d-block elements are also classified as transition elements.

Explain why scandium and zinc are classified as d-block elements but are not also transition elements.

Your explanations should include full electron configurations.

What is meant by a bidentate ligand ?

* Determine the formulae of A and B. Write the ionic equation for the ligand substitution and show 3D structures for the three stereoisomers of B.

What is the number of stereoisomers that Ni(H₂NCH₂CH₂NH₂)₂Cl₂ can form?

A 2

B 3

C 4

D 6

Your answer

This question is about reactions of ions and compounds of transition elements.

A student carries out two experiments on a solution containing [Cr(H₂O)₆]³⁺(aq).

Experiment 1 The student adds an excess of aqueous ammonia to a solution containing [Cr(H₂O)₆]³⁺ until a purple solution is formed.

Experiment 2 The student carries out the following reaction sequence.

Step 1 NaOH(aq) is added slowly to a solution containing [Cr(H₂O)₆]³⁺(aq) in a boiling tube. A grey–green precipitate forms.

Step 2 An excess of NaOH(aq) is added to the boiling tube. The precipitate dissolves and a green solution forms containing a 6 coordinate complex ion.

Step 3 H₂O₂ is added to the mixture and the boiling tube is heated. A yellow solution forms.

Step 4 The solution in the boiling tube is acidified. The solution now contains Cr₂O₇²⁻(aq).

What is the formula of the complex ion in the purple solution that forms in Experiment 1

Suggest an equation for the reaction in Experiment 2, Step 1. Include state symbols.

Draw a 3-D diagram for the shape of the complex ion that forms in Experiment 2, Step 2 Include the charge of the ion.

What is the formula of the ion that causes the yellow colour in Experiment 2, Step 3

State the colour of the solution that forms in Experiment 2, Step 4.

Vanadium ions have four common oxidation states. Table 18.1 shows the colours of the ions in aqueous solution.

Complete the electron configuration of a V³⁺ ion.

The student adds excess iron to a solution containing VO²⁺(aq) ions, and observes that the colour of the solution changes from blue to green and then to violet.

Use the relevant standard electrode potentials shown in Table 18.2 to explain these observations.

Construct an equation for the first colour change from blue to green.

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.

Stage 1 The student crushes two tablets and dissolves the powdered tablets in dilute sulfuric acid.

Stage 2 The student makes up the solution from Stage 1 to 250.0 cm³ in a volumetric flask.

Stage 3 The student then titrates 25.0 cm³ portions of the solution obtained in Stage 2 with 0.00200 mol dm⁻³ potassium manganate(VII).

The student obtains a mean titre of 13.50 cm³.

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

Explain why the student used 0.00200 mol dm⁻³ potassium manganate(VII) solution for this titration, rather than the more usual concentration of 0.0200 mol dm⁻³ used in manganate(VII) titrations.

Use the student’s results to determine the mass, in mg, of iron(II) gluconate in one tablet.

Give your answer to 3 significant figures.

Which statement(s) is/are correct for the complex Pt(NH₃)₂Cl₂?

1 One of its stereoisomers is used as an anti-cancer drug.

2 It has bond angles of 109.5°.

3 It has optical isomers.

A 1, 2 and 3

B Only 1 and 2

C Only 2 and 3

D Only 1

Your answer

This question is about some reactions of d block elements and their ions.

Table 21.1 shows standard electrode potentials which will be needed within this question.

Complete the electron configuration of

a Ni atom: 1s²........

a Ni²⁺ ion: 1s²........

A standard cell is set up in the laboratory with the cell reaction shown below.

Draw a labelled diagram to show how this cell could be set up to measure its standard cell potential.

Include details of apparatus, solutions and the standard conditions required.

Standard conditions........

Predict the standard cell potential of this cell.

Use the information in Table 21.1 to help you answer both parts of this question.

Write the overall equation for the oxidation of Fe²⁺ by acidified H₂O₂.

Zinc reacts with acidified Cr₂O₇^2– ions to form Cr²⁺ ions in two stages.

Explain why this happens in terms of electrode potentials and equilibria.

Include overall equations for the reactions which occur.

* Three different reactions of copper compounds are described below.

Reaction 1: Aqueous copper(II) sulfate reacts with excess aqueous ammonia in a ligand substitution reaction. A deep-blue solution is formed, containing an octahedral complex ion, C, which is a trans isomer.

Reaction 2: Copper(I) oxide reacts with hot dilute sulfuric acid in a disproportionation reaction. A blue solution, D, and a brown solid, E are formed.

Reaction 3: Copper(II) oxide reacts with warm dilute nitric acid in a neutralisation reaction, to form a blue solution. Unreacted copper(II) oxide is filtered off, and the solution is left overnight in an evaporating basin. A hydrated salt, F, crystallises, with the percentage composition by mass: Cu, 26.29%; H, 2.48%; N, 11.59%; O, 59.63%.

Identify C – F by formulae or structures, as appropriate.

Include equations, any changes in oxidation number, and working.

Ethanedioic acid, (COOH)₂, is present in rhubarb leaves.

A student carries out a redox titration using aqueous cerium(IV) sulfate, Ce(SO₄)₂(aq), to determine the percentage, by mass, of ethanedioic acid in rhubarb leaves.

In the titration, Ce⁴⁺(aq) ions oxidise ethanedioic acid in hot acid conditions:

Ce⁴⁺(aq) ions have a yellow colour. Ce³⁺(aq) ions are colourless.

The student weighs 82.68 g of rhubarb leaves and extracts ethanedioic acid from the leaves.

The ethanedioic acid is added to dilute sulfuric acid to form a colourless solution which is made up to 250.0 cm³ with distilled water.

The student heats 25.00 cm³ of this solution to 70 °C and titrates this volume with 0.0500 mol dm^–3 Ce(SO₄)₂ from the burette.

The student repeats the titration to obtain concordant (consistent) titres.

Titration results The trial titre has been omitted.

This titration is self-indicating and the student does not need to add an indicator.

What colour change would the student observe at the end point?

Colour change from........ to........

Calculate the percentage, by mass, of ethanedioic acid in the rhubarb leaves.

Give your answer to an appropriate number of significant figures.