[SOLVED] CHEMISTRY 9620 Unit 3 Inorganic 2 and Physical 2

INTERNATIONAL A-LEVEL

CHEMISTRY (9620)

Unit 3: Inorganic 2 and Physical 2

One of the characteristics of transition metals is that they form. complexes.

A solution contains aqueous copper(II) ions.

When an excess of chloride ions is added to this solution, a reaction occurs in which there is a change in the co-ordination number of the copper ion.

• Write an equation for the reaction.

• State the type of reaction occurring.

• State the name of the shape of the complex ion formed.

• Give a reason for the change in co-ordination number.

[4 marks]

Equation

Type of reaction

Name of the shape of the complex ion

Reason for change in co-ordination number

Explain why transition metal complexes are coloured.

[3 marks]

State why there is often a colour change when there is a change in ligand in a reaction involving a complex.

[1 mark]

Figure 1 shows the structure of a complex ion of copper.

Figure 1

State the co-ordination number of copper in the complex ion shown in Figure 1.

[1 mark]

Name the species that acts as a bidentate ligand in the complex ion shown in Figure 1.

State how this species can act as a bidentate ligand.

[2 marks]

Name

How species acts as a bidentate ligand

Identify a reagent that could be used in a test to show that [Fe(H2O)6]
3+ is a better proton donor than [Fe(H2O)6]
2+

Describe the expected result of your test.

[2 marks]

Reagent

Observations

This question is about some Period 3 oxides and chlorides.

Suggest why silicon dioxide can be described as an acidic oxide even though it is insoluble in water.

[1 mark]

Table 1 shows the melting points of some Period 3 oxides.

Table 1

Explain, in terms of structure and bonding, why sodium oxide has a high melting point.

[3 marks]

Explain why sulfur trioxide has a higher melting point than sulfur dioxide.

[2 marks]

A small amount of each of the Period 3 chlorides NaCl, MgCl2, AlCl3 and PCl5 is added to separate samples of deionised water.

The pH values of the resulting solutions are measured.

State why NaCl forms a neutral solution.

[1 mark]

Both AlCl3 and PCl5 form. acidic solutions.

The equation for the reaction of AlCl3 with water is

Explain why the solution formed is acidic. Use an equation in your answer.

[2 marks]

Identify the two acids formed when PCl5 reacts with water.

[1 mark]

Born–Haber cycles can be used to show the enthalpy changes involved in the formation of an ionic compound.

Figure 2 shows an incomplete Born–Haber cycle for the formation of potassium oxide (K2O).

The Born–Haber cycle is not to scale.

Figure 2

Complete Figure 2 by writing the formulae, including state symbols, of the appropriate species on each of the two blank lines.

[2 marks]

Table 2 shows the enthalpy changes involved in the formation of potassium oxide.

Table 2

Give the meaning of the term enthalpy of atomisation.

[2 marks]

Suggest why the second electron affinity of oxygen is endothermic.

[1 mark]

Use the data in Table 2 to calculate the enthalpy of lattice dissociation of potassium oxide.

[3 marks]

enthalpy of lattice dissociation = kJ mol–1

A theoretical value for the enthalpy of lattice dissociation can be calculated using a perfect ionic model.

The theoretical enthalpy of lattice dissociation for silver fluoride is +870 kJ mol–1

Explain why the theoretical enthalpy of lattice dissociation for silver fluoride is different from the experimental value calculated using a Born–Haber cycle.

[2 marks]

The theoretical enthalpy of lattice dissociation for silver chloride is +770 kJ mol–1

Explain why this value is less than the value for silver fluoride.

[2 marks]

Ethyne gas (C2H2) is manufactured from methane in a reversible reaction.

What is the effect of increasing the pressure on the equilibrium yield of ethyne and on the equilibrium constant (Kp) for this reaction?

[1 mark]

Tick () one box.

Write an expression for Kp for the manufacture of ethyne from methane.

[1 mark]

Kp

At a given temperature a sealed flask contains an equilibrium mixture of 0.10 mol of methane, 0.18 mol of ethyne and 0.52 mol of hydrogen. The pressure in the flask at equilibrium is 500 kPa

Calculate the value of Kp under these conditions.

Give your answer to three significant figures.

State the units of Kp

[4 marks]

Figure 3 represents an alkaline fuel cell.

Figure 3

Give two reasons why it is not correct to describe the cell in Figure 3 as a rechargeable cell.

[2 marks]

1

2

Gas B is oxygen.

Identify Gas A and Liquid C.

[2 marks]

Gas A

Liquid C

It would be cheaper to use air instead of pure oxygen. One disadvantage of using air is that the carbon dioxide in the air would react with the electrolyte and decrease the life of the cell.

Complete the equation for the reaction between carbon dioxide and the electrolyte, KOH

[1 mark]

An equation for the reaction at the positive electrode is

Write an equation for the reaction at the negative electrode.

[1 mark]

Use the two equations in Question 05.4 to deduce an overall equation for the fuel cell.

[1 mark]