Oxidation states

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 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 energy changes.

Hydrogen peroxide decomposes as shown in Reaction 16.1.

The table shows enthalpy changes of formation and entropies.

	Hf / kJ mol–1	S / J K–1 mol–1
H2O2(l)	–188	110
H2O(l)	–286	70.0
O2(g)	0	205

Calculate the free-energy change, G, in kJ mol^–1, of Reaction 16.1 at 25 C.

Give your answer to 3 significant figures.

G =........ kJ mol^–1

The decomposition of hydrogen peroxide shown in Reaction 16.1 is feasible.

Suggest why Reaction 16.1 does not take place at 25 C despite being feasible.

The rate of decomposition of hydrogen peroxide shown in Reaction 16.1 can be increased by adding a small amount of powdered manganese(IV) oxide, MnO₂.

The MnO₂ acts as a catalyst.

Complete the enthalpy profile diagram for Reaction 16.1 using formulae for the reactants and products.

• Use E_a to label the activation energy without MnO₂.

• Use E_c to label the activation energy with MnO₂.

• Use H to label the enthalpy change of reaction.

Explain why MnO₂ is described as a heterogeneous catalyst for this reaction.

Mn₃O₄ is a compound in which Mn has two different oxidation states. The two oxidation states are different from the Mn in MnO₂.

Suggest the two oxidation states of manganese in Mn₃O₄.

Define the term lattice enthalpy.

Calculate the lattice enthalpy of MnO.

lattice enthalpy =........ kJ mol^–1

This question is about the chemistry of compounds containing phosphorus.

Phosphorus forms several acids including H₃PO₄ and H₃PO₃.

H₃PO₄ is a tribasic acid. The equilibria for the dissociations are shown below.

During the equilibria, H₂PO₄^– behaves both as an acid and as a base.

Explain this statement, using the equilibria 1, 2 and 3, as required.

In a H₃PO₃ molecule, the O atoms are covalently bonded to the P atom. The H atoms are bonded to the O atoms.

Draw the structure of a H₃PO₃ molecule, showing all the bonds.

On your diagram, add the values for the O–P–O and P–O–H bond angles.

The systematic name of H₃PO₄ is phosphoric(V) acid.

What is the systematic name of H₃PO₃?

Phosphine, PH₃, is a poisonous gas.

Phosphine reacts with oxygen gas to form phosphorus(V) oxide and water.

Write the equation for this reaction.

Aqueous silver nitrate, AgNO₃, is reduced by PH₃. The unbalanced equation is shown below.

Balance the equation and use oxidation numbers to explain why this is a redox reaction.

Explanation........

When phosphorus(V) chloride, PCl₅, and ammonium chloride are heated together, the compound P₃N₃Cl₆ is formed, together with HCl gas.

P₃N₃Cl₆ has a cyclic structure, like the Kekulé structure of benzene.

Write an equation for the reaction of PCl₅ and ammonium chloride to form P₃N₃Cl₆.

Calculate the percentage by mass of P in P₃N₃Cl₆.

Give your answer to 2 decimal places.

Suggest one example of evidence that could show that P₃N₃Cl₆ has a Kekulé structure rather than a delocalised structure.

In a molecule of P₃N₃Cl₆ all the N and Cl atoms are bonded to P atoms.

Suggest a possible structure for a molecule of P₃N₃Cl₆.

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

These questions are from different areas of chemistry.

This question is about two salts of rubidium (atomic number 37): RbClO₃ and RbClO₄.

The oxidation number of chlorine is different in the two rubidium salts, RbClO₃ and RbClO₄.

What is the name of RbClO₄?

A student carries out an experiment to determine the enthalpy change of solution of RbClO₃ using the method below.

• A 2.00 g sample of solid RbClO₃ is added to water in a well-insulated container. The initial temperature is 23.0 °C.

• The mixture is stirred until all the RbClO₃ has dissolved. The final temperature is 21.5 °C. The final solution has a mass of 102 g.

Determine the enthalpy change of solution, _solH, of RbClO₃ in kJ mol^–1.

Assume that the specific heat capacity of the solution is the same as that of pure water.

_solH (RbClO₃) =........ kJ mol^–1

A student investigates the rate of a reaction that is 1st order with respect to hydrochloric acid, HC l (aq).

• The student carries out a reaction using 0.680 mol dm^–3 HCl(aq). The initial rate is

• The student dilutes a different sample of 0.680 mol dm^–3 HCl(aq) with water. The pH of this diluted acid is 1.50.

• The student repeats the reaction using the same volume of this diluted acid.

Determine the initial rate using this diluted acid.

initial rate =........ mol dm^–3 s^–1

Prussian blue, C₁₈Fe₇N₁₈, is a deep blue pigment containing Fe²⁺, Fe³⁺ and CN⁻ ions.

What are the numbers of Fe²⁺ and Fe³⁺ ions in one formula unit of C₁₈Fe₇N₁₈?

A 2 Fe²⁺ and 5 Fe³⁺

B 3 Fe²⁺ and 4 Fe³⁺

C 4 Fe²⁺ and 3 Fe³⁺

D 5 Fe²⁺ and 2 Fe³⁺

Your answer

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

A chlorate(VII) ion has a 1– charge.

What is the formula for sodium chlorate(VII)?

A NaCl O₃

B NaCl O₄

C NaCl O₇

D NaCl O₈

Your answer

What is the oxidation number of N in Mg(NO₂)₂•3H₂O?

A +2

B +3

C +4

D +5

Your answer

In the compound [ICl₂]⁺ [SbCl₆]^–, the oxidation number of chlorine is –1.

What are the oxidation numbers of I and Sb in the compound?

Your answer

Select an element from the first three periods that fits each of the following descriptions.

The element that forms a 1– ion with the same electron configuration as helium.

The element with the highest first ionisation energy.

The element in Period 3 which has the successive ionisation energies shown below.

The element which forms a compound with fluorine that has octahedral molecules.

An element which reacts with water to form an acidic solution.

The element X, which forms a compound with hydrogen, XH₃, with a molar mass of 34.0 g mol^–1.

An element which forms a compound with hydrogen in which the element has an oxidation number of –4.

The element which has a density of 1.33 × 10^–3 g cm^–3 at room temperature and pressure.

Table 1.1 shows some properties of Period 3 chlorides.

Explain the properties shown in Table 1.1 in terms of bonding and structure.

This question is about two compounds used in medicine.

Cis-platin, PtCl₂(NH₃)₂, is a complex of platinum which is used in cancer treatment.

What is the oxidation number of platinum in cis-platin?

Cis-platin is prepared in a ligand substitution reaction which takes place in multiple steps.

The equation for the final step forming cis-platin is shown below.

cis-platin

In the box, outline the mechanism for the formation of cis-platin from [PtCl₃(NH₃)]^–. Use curly arrows and lone pairs where appropriate.

cis-platin

Paracetamol is a solid organic compound used in tablets as a painkiller.

Name the functional groups present in paracetamol.