Inorganic Chemistry

(12)1, 16

Which reaction will not take place readily under the conditions specified by the state symbols? [Note: H2O(g) = steam]

A. Ba ( s )+2 H 2 O(l)→ Ba ¿

B. CaO ( s )+H 2O(l)→ Ca¿

C. Mg ( s )+H 2O (g )→ MgO (s )+H 2(g)

D. Mg ( s )+2 H 2 O (l ) → Mg (OH )2 (aq )+H 2(g)

(12)1, 31

Which statements correctly describe the graphite lattice?

1. The lattice contains delocalised electrons.2. Each carbon atom in the lattice has three closest neighbours.3. The valency of each carbon atom in the lattice is 3.

(11)1, 14

Which statement concerning only the elements in the third period, sodium to argon, is correct?

A. The element that has exactly four atoms in its molecule is sulfur.B. The element with the highest electrical conductivity is aluminium.C. The element with the highest melting point is aluminium.D. The element with the largest anion is chlorine.

(11)1, 16

Use of the Data Booklet is relevant to this question.

What volume of oxygen, measured under room conditions, can be obtained from the complete thermal decomposition of 8.2g of calcium nitrate (Mr = 164)?

A. 150cm3

B. 300cm3

C. 600cm3

D. 1200cm3

(10)1, 31

Given weighed samples of the same mixture of magnesium carbonate and barium carbonate, how can the mole fraction of magnesium carbonate in the mixture be estimated?

1. Add a known volume of 0.1moldm-3 HCl(aq), in excess, and back titrate the excess of acid.

2. Add an excess of HCl(aq) and measure, at know temperature and pressure, the volume of CO2 liberated.

3. Add an excess of HCl(aq) followed by an excess of H2SO4(aq); filter, dry and weigh the precipitate.

(10)1, 35

Above-ground tests of nuclear explosions in the mid-20th century resulted in pollution by radioactive 90Sr. It is an intense emitter of electrons that can damage body cells.

Three properties of strontium are listed.

Which of these properties help to explain why this pollution caused particular concern?

1. Strontium sulfate has low solubility.2. 90Sr has a half-life of 29 years.3. Strontium is immediately below calcium in Group II.

(09)1, 5

Which feature is present in the ions carbonate, ethanoate, nitrate and phenoxide (phenate)?

A. All bond angles are 120°B. Dative covalent bondsC. Delocalised electronsD. Hydrogen bonds

(09)1, 6

What is a property of a solution of dry hydrogen chloride in dry methylbenzene?

A. It has a pH less than 7.B. It is a non-conductor of electricity.C. It reacts with magnesium to give hydrogen.D. It reacts with anhydrous sodium carbonate to give carbon dioxide.

(09)1, 14

Aluminium hydroxide has a decomposition temperature of 573K. It is mixed with titanium chloride to produce a paint which delays the spread of flames in the event of a fire.

Which statement explains why aluminium hydroxide is used in this way?

A. It is acidic enough to absorb any ammonia produced in a fire.B. Water vapour is produced on decomposition.C. It reacts with acid produced on combustion.D. A large amount of energy is adsorbed when aluminium hydroxide vaporises.

(09)1, 19

Predict the most likely bond angle at each nitrogen atom in di-imine, HN=NH.

A. 107°B. 118°C. 120°D. 180°

(09)1, 32

Which statements concerning the lattice structures of graphite and diamond are correct?

1. The C-C-C bond angle between nearest neighbours is smaller in diamond than in graphite.

2. The shortest carbon-carbon bond occurs in diamond.3. All covalent bonds in diamond are of the same strength but those in graphite are not.

(09)1, 35

Use of the Data Booklet is relevant to this question.

Hydroxyapatite, a basic calcium phosphate, Ca(OH)2.3Ca3(PO4)2, is the mineral found in bone.

Older people may lose calcium ions from the hydroxyapatite, weakening the bond structure. For such cases, strontium salts are administered to strengthen the bone. The strontium ions replace the lost calcium ions in the hydroxyapatite.

Which statements are correct?

1. Strontium ions are nearly the same size as calcium ions and so may easily replace them in the hydroxyapatite.

2. Strontium hydroxide is more soluble than calcium hydroxide and so will precipitate better in the bone structure.

3. There is ionic, covalent and metallic bonding in hydroxyapatite which gives it strength.

(12)3, 1

a) The acid-base behaviour of aluminium oxide, Al2O3, shows similarities to that of magnesium oxide, MgO, on the one hand, and phosphorus(V) oxide, P4O10, on the other.Describe what three similarities are, and explain why aluminium oxide occupies this in-between position.Write equations for all the reactions you choose to illustrate your answer. [5]

b) The following equilibrium exists in a sample of aluminium chloride vapour. [11]

A l2C l6(g)⇌2 AlC l3(g) ΔH = +63 kJmol-1

i. Draw a dot-and-cross diagram of the Al2Cl6 molecule including its co-ordinate (dative covalent) bonds.

ii. Suggest the shape of the AlCl3 molecule.

iii. Predict the effect of increasing the temperature on the above equilibrium. Explain your answer.

When 1.50g of aluminium chloride was introduced into an evacuated flask of 250cm3 capacity and heated to 500K, the pressure inside the flask rose to 1.16 x 105Pa.

iv. Assuming the gaseous mixture behaves ideally, use the general gas equation to calculate the average Mr of the mixture.

v. Using the following relationships, calculate the mole fraction of Al2Cl6, x, and the mole fraction of AlCl3, y, in the mixture.

x+ y=1M r (average )=267 x+133.5 y

vi. Hence calculate the partial pressures of Al2Cl6 and AlCl3 in the mixture.

vii. Write an expression for Kp for the reaction, and calculate its value. Include units in your answer.

(12)3, 4

Beams of charged particles are deflected by an electric field. If the particles are all travelling at the same speed, through an electric field of constant strength, the angle of deflection is proportional to their charge/mass ratio.

In a particular experimental set-up, protons are deflected through an angle of +15°.

a) Assuming an identical set of experimental conditions, by what angles will the following particles be deflected? (D is deuterium, 2H, and T is tritium, 3H) [3]D-

T+

He2+

b) Under identical conditions, a beam of particles, R, each having 12 times the mass of a proton, was deflected by an angle of +5°. [3]

i. Suggest the overall charge on a particle of R.

ii. Given that a particle of R contains 6 protons, deduce the number of neutrons and electrons in a particle of R.

c) [6]i. Some ionic radii are listed in the Data Booklet.

State and explain the differences between the ionic radii of Na, Si, P and Cl.

ii. These four elements also differ greatly in their melting points. Describe how their melting points differ, and explain this variation.

(11)3, 2

a) The calcium salt E has the formula CaCxOy. When 1.00g of E was heated strongly, 386cm3 of a mixture of two gases (measured at 298K and 1.00 x 105Pa) was produced, and 0.438g of a white solid remained. The addition of an excess of NaOH(aq) to the gaseous mixture caused its volume to decrease by 193cm3. [5]

i. Calculate the average Mr of the gaseous mixture.

ii. Suggest the identity of the gas that reacted with NaOH(aq).

iii. Hence calculate the Mr of the other gas in the gaseous mixture, and suggest its identity.

iv. Suggest the formula of E and write a balanced equation for its thermal decomposition.

Dicarboxylic acids can ionise in stages.

HO2C-(CH2)n-CO2H HO2C-(CH2)n-CO2- -O2C-(CH2)n-CO2

-

b) The following table compares the pKa values of one of these dicarboxylic acids with that of ethanoic acid. [7]

Acid Formula pK1 pK2

Ethanoic CH3CO2H 4.76 -Malonic HO2CCH2CO2H 2.85 5.70

i. Suggest a reason why the pK1 value of malonic acid is so much less than the pK1 of ethanoic acid.

ii. Suggest a reason why the pK2 value of malonic acid is higher than the pK1 of ethanoic acid.

iii. Calculate the pH of a 0.10moldm-3 solution of malonic acid (ignore the effect of pK2 on the pH).

iv. Sketch the pH-volume added curve you would expect to obtain when 30cm3 of 0.10moldm-3 NaOH is added to 10cm3 of 0.10moldm-3 malonic acid.Briefly describe how you have calculated the various key points on the curve.

-H+

pK1

-H+

pK2

(09)2, 1

Sodium chloride, sodium bromide, sodium iodide and magnesium oxide are ionic compounds which all have the same crystal structure.

Lattice energies can be used as a measure of the energetic stability of ionic compounds.

a) Define, with the aid of an equation, the lattice energy of magnesium oxide. [2]

Lattice energies are not measured directly. By using Hess’ Law and the Born-Haber cycle, they can be obtained from experimental data. From knowledge of the distances between the cations and anions in the crystal structure, and the charge on each ion, it is also possible to calculate theoretical values for lattice energies.The table below shows numerical values of lattice energies for the sodium halides, magnesium oxide and two silver halides. These have been determined from experimental data or theoretically calculated.

Compound Experimental value /kJmol-1 Theoretical value /kJmol-1

NaCl -781 -766NaBr -743 -730NaI -699 -685

MgO -3933 -AgF -967 -953AgI -889 -808

b) By quoting approximate appropriate data from the Data Booklet, [6]i. Explain why the lattice energies of the sodium halides decrease from NaCl to

NaI,

ii. Suggest why the lattice energy of MgO is considerably larger than those of sodium halides.

c) Silver fluoride and silver iodide have the same crystal structure. Like the sodium halides, there is close agreement between the experimental and theoretical values of lattice energy for AgF but not for AgI.Suggest a reason for this. [1]

d) In the crystal lattice of sodium and potassium chlorides, the co-ordination number of each ion is 6. In the crystal lattice of caesium chloride, CsCl, the co-ordination number has a different value. [3]

i. Suggest what is meant by the term co-ordination number when used to refer to a crystal lattice.

ii. Suggest an explanation for the co-ordination number in the CsCl lattice being different from those in NaCl and KCl.