4 : Bonding and Structure A.L. BOSCO P.1

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1 80.I.B.6.a. 4 : Bonding and Structure A.L. BOSCO P.1 M + (g) + Cl - (g) M + Cl - (s) ( M is a metal ) ΔH O 298 = kj mol 1 (i) What is the term given to the enthalpy change assoicated with this reaction? With reference to the equation, explain the meaning of this term. ( 3 (ii) The experimental value of the above enthalpy change ( kj mol 1 ) is determined indirectly using a Born-Haber cycle. Draw and label the Born-Haber cycle used. ( 2 (iii) Using the principles of electrostatics, the theoretical value of ΔH O 298 for M + Cl (s) is kj mol 1. The corresponding values for silver chloride are also known. The two sets of values are given in the following table : ΔH O 298 / kj mol 1 Compound Theoretical Experimental M + Cl (s) Ag + Cl (s) (I) What basic assumptions are made in determining the theorectical value? (II) Why is there no difference between the theoretical and experimental values in the case of M + Cl (s) and a large difference in the case of Ag + Cl (s)? (III) To which group in the Periodic Table do you think does metal M belong? Explain. ( 5

2 4 : Bonding and Structure A.L. BOSCO P.2 82.I.B.7.b. Determine the enthalpy of formation of magnesium carbonate at room temperature by using the results from the two simple experiments below. Experiment A : The temperature of stirred solution of cm 3 of 2.0 M hydrochloric acid in a polythene beaker was noted at half-minute intervals. At exactly 2.5 minutes, g of magnesium ribbon was added and the temperature readings were continued. The results were as follows : Time / min Temperature / o C Mg added Time / min Temperature / o C (i) Plot a graph to show the change in temperature with time. ( 2 (ii) Write an equation for the reaction in Experiment A and calculate its enthalpy change. You may assume that the density of the solution is 1.0 g cm -3 and that the solution has the same specific heat capacity as water, i.e. 4.2 J g -1 K -1. ( 4

3 Experiment B : 4 : Bonding and Structure A.L. BOSCO P.3 This was similar to Experiment A except that magnesium carbonate was used in the place of the magnesium ribbon. The enthalpy of reaction between magnesium carbonate and hydrochloric acid in Experiment B was found to be 43.5 kj mol -1. You are provided with further information as following : H 2 (g) + ½ O 2 (g) == H 2 O (l) ΔH = kj mol -1 C (s) + O 2 (g) === CO 2 (g) ΔH = kj mol -1 (iii) Construct a Born-Haber cycle and determine the enthalpy of formation of magnesium carbonate. ( 5 (iv) Point out two probable errors which might lead to the results being imprecise, and suggest how these errors could be reduced. ( 4 ( relative atomic mass : Mg = 24.3 ) 82.II.B.6.a. Given that the bond energy ( in kj mol -1 ) of M O is 466, and that of M = O is 643, estimate the heat of reaction per R 2 MO unit for monomer polymer R R 2 n R 2 MO M O M O R R n Which species, monomer or polymer, would you expect to be more stable? Give your reasons. ( 3 83.I.A.2.b.

4 4 : Bonding and Structure A.L. BOSCO P.4 Comment on the variation in the bond dissoication energies for the halogen family : Halogen F F Cl Cl Br Br I I Bond dissociation energy / kj mol -1 at 298 K ( 4 84.I.B.6. (a) The combustion of 0.39 g of benzene produced a temperature rise of 4.85 K in a calorimeter containing water. The same rise in temperature was obtained by heating this calorimeter with an electric current of 1.6 A at 12.5 V for 817 s. (i) Determine the enthalpy of combustion of benzene. (ii) Given that the enthalpies of formation of CO 2 (g) and H 2 O (l) are 393 kj mol - 1 and 286 kj mol -1 respectively, calculate the enthalpy of formation of benzene. relative atomic masses : H = 1.0, C = 12.0 ( 8 (b) Using the information provided below, explain how you can predict the enthalpy of formation of benzene. Compare your result with the value obtained in (a) and comment on the difference, if any. Bond C H C C C = C Bond energy / kj mol Reaction C (s) C (g) ½ H 2 (g) H (g) C 6 H 6 (l) C 6 H 6 (g) Δ H / kj mol ( 9 85.I.C.1.

5 4 : Bonding and Structure A.L. BOSCO P.5 Explain how values of lattice energy may be derived from suitable thermochemical data ; comment on any differences between experimentally derived and theoretical values. Show how lattice energies may be used to obtain values for the enthalpy of solvation of ions. Note : You may make use of the following information : lattice energy / kj mol -1 NaBr AgBr theoretical experimental ( II.A.2.a. A Form 6 student carried out the following experiments to determine the standard enthalpy of dissociation of RCO 2 H. Experiment (I) Experiment (II) 50 cm 3 of 2.0 M NaOH solution were added to 50 cm 3 of 2.0 M HCl solution in a polystyrene cup. The maximum temperature rise was found to be 13.0 o C. equation : H + (aq) + OH - (aq) = H 2 O (l) 50 cm 3 of 2.0 M NaOH solution were added to 50 cm 3 of 2.0 M RCO 2 H solution in a polystyrene cup. The maximum temperature rise was found to be 10.5 o C. equation : RCO 2 H (aq) + OH - (aq) = RCO - 2 (aq) + H 2 O (l) Given at 298 K and 1 atmosphere pressure : specific heat capacity of the solution = 4.2 J g -1 K -1. Density of the soluion = 1.0 g cm -3. (i) Calculate the standard enthalpy of neutralization for experiment (I) and experiment (II) respectively. Explain the difference in values obtained. (ii) Calculate the standard enthalpy of dissociation of RCO 2 H. ( 8 86.II.A.2.b.

6 4 : Bonding and Structure A.L. BOSCO P.6 Define the lattice energy of an ionic crystal. What information can be obtained from a comparison of the theoretical value with the experimentally determined Born-Haber value? ( 4 86.II.A.2.c. Draw an energy diagram and calculate the lattice energy of calcium fluoride using the following data : standard enthalpy of formation of calcium fluoride 1203 kj mol 1 standard enthalpy of sublimation of calcium metal 193 kj mol 1 first ionization energy of calcium 590 kj mol 1 second ionization energy of calcium 1145 kj mol 1 standard enthalpy of dissociation of flouride molecules 158 kj mol 1 electron affinity of fluorine atoms 333 kj mol 1 ( 6 89.II.A.1.a. For the reaction : H 2 (g) + C 2 H 4 (g) C 2 H 6 (g), (i) calculate the enthalpy of the above reaction by two different methods using (I) the enthalpy of formation at 298 K ΔH O f of C 2 H 4 (g) = kj mol -1 ; ΔH O f of C 2 H 6 (g) = 84.6 kj mol -1 (II) the average bond energies at 298 K H H kj mol -1 ; C H kj mol -1 ; C=C kj mol -1 and C C kj mol -1. (ii) Comment on the difference between the enthalpy of reaction obtained by 2 methods. ( 7 91.II.A.1.b.

7 4 : Bonding and Structure A.L. BOSCO P.7 (i) Calculate the enthalpy of formation of NaCl (s) from the following data : Reaction ΔH O / kj mol -1 (ii) (iii) NaOH (aq) + HCl (aq) NaCl (aq) + H 2 O (l) 57.3 H 2 (g) + ½ O 2 (g) H 2 O (l) ½ H 2 (g) + ½ Cl 2 (g) HCl (g) 92.3 HCl (g) + aq HCl (aq) 71.9 Na (s) + ½ O 2 (g) + ½ H 2 (g) + aq NaOH (aq) NaCl (s) + aq NaCl (aq) 3.9 The enthalpy of neutralization of ethanoic acid with aqueous sodium hydroxide is 55.2 kj mol -1 while that of hydrochloric acid is 57.3 kj mol -1. Account for the difference in these two values. When solid sodium hydroxide is dissolved in water, the process is endothermic. Explain this observation. ( 8 80.I.B.7.d. Diffraction studies on gaseous nitric (V) acid show that it contains two different N O bonds with lengths of nm and nm, respectively. (i) Draw the structure of a nitric (V) acid molecule, indicating the values of bond length and giving approximate bond angles. ( 2 (ii) Why are there two different bond lengths in nitric (V) acid? ( 2 (iii) What would you expect the bond lengths of the N O bonds to be in a nitrate ion? ( 1 81.I.A.4.d.ii. What is the hybridisation in the bonding of nitrogen in the NH 4 + ion? ( 1

8 4 : Bonding and Structure A.L. BOSCO P.8 81.I.B.7.a. & b. (a) (b) Discuss the difference in the carbon-carbon distances in diamond and graphite. ( 5 It has been said that pure ionic and pure covalent bonds only represent extreme bond types. Do you agree with this statement? Justify your answer. ( 7 82.I.A.2.b. Complete the following table on the classification of crystalline solids : Ionic Covalent Molecular Metallic Units constituting the crystal lattice Binding force holding the constituent units Example ( one each ) 82.I.A.4.c. + ve and ve ions sodium chloride ( 5 Describe and draw the structures of : (i) CO 2 (ii) SO 2 ( 2

9 4 : Bonding and Structure A.L. BOSCO P.9 82.I.b.6.a. Benzene is a planar molecule where the density of electrons is greatest above and below the molecular plane. Discuss the above statement in the light of the types of hybridization involved. You should illustrate your answer with sketches. ( 8 82.II.B.10.c. Decide whether the following statements are true or false and give reasons : (i) Covalent bonding in oxygen is stronger that that in nitrogen because the boiling points of O 2 and N 2 are 85 K and 77 K, respectively. ( 3 (ii) The bond formed in sodium chloride is purely ionic. ( 2 83.I.A.2.a. Consider the three species : NO 2, NO - 2, and NO + 2. (i) Draw the structure of each species. ( 3 (ii) Why does NO 2 have a larger bond angle than NO - 2? ( 1 83.I.B.6.b. Compare the shape and bond angles of the following molecules : H 2 S, NH 3, SiH 4 on the basis of electron-pair repulsion theory. ( 6 83.I.B.6.d.

10 4 : Bonding and Structure A.L. BOSCO P.10 Graphite and diamond are both pure carbon. Why does graphite conduct electricity, whereas diamond does not? ( 3 84.I.A.2. (a) The figure below shows the electron density map of a hydrocarbon, C 14 H 10 : (b) (i) Name the technique used to obtaine this map. (ii) Draw the molecular structure of the hydrocarbon. (iii) Comment on the clarity of this map in showing the position of all the atoms. ( 4 Comment on the relative carbon-oxygen bond lengths in CH 3 COOH molecules and CH 3 COO ions. ( 2 84.I.B.6.c. Account for the presence or absence of a dipole moment in a 1, 2-dichlorobenzene molecule and a 1, 4-dichlorobenzene molecule. ( 3

11 4 : Bonding and Structure A.L. BOSCO P I.A.1.a. Define the term dative covalent bond. Give one example to illustrate your answer. ( 2 85.I.A.3.a. Describe, with the aid of labelled diagrams, the bonding in benzene in terms of the overlap of the different types of orbitals. ( 5 86.I.A.1.b. (i) Account for the fact that both CH 4 and NH 3 have shapes based on the tetrahedron. (ii) Deduce the shape of BF 3. ( 4 86.I.A.2.b. Using dot and cross diagrams, show the bonding involved in the three species : O 2, O 2 2-, O 2 -. Arrange the three species in order of increasing bond energy. ( 4 87.I.A.2.a.i. Draw the structure of the aluminium chloride dimer and comment briefly on its bonding. ( 2

12 4 : Bonding and Structure A.L. BOSCO P II.A.3.b. (i) (ii) (iii) Define the covalent radius of an atom. State and explain the trends in the covalent radius on going down any group and going across a short period of the periodic table. The covalent radius of carbon is nm. The measured carbon-carbon bond length in benzene is nm. Estimate the carbon-carbon bond length in ethane. Explain why difference in the carbon-carbon bond lengths in these two molecules. ( 6 81.I.A.2.a. At room temperature, both oxygen and butane may be stored under pressure in steel cylinders. Under these conditions, oxygen is in the gaseous state, whereas butane is a liquid. Suggest an explanation for this difference. ( 2 81.I.B.5.c. Wet knitting wood stretches more than dry knitting wool. Suggest an explanation for this in terms of the changes in bonding which occur when knitting wool becomes wet. ( 2

13 4 : Bonding and Structure A.L. BOSCO P I.A.2.c. & d. (c) Fine jets of water and tetrachloromethane are separately run from a burette into a beaker, as shown in the diagram below : What would you expect to observe when a positively charged glass rod is brought near to each liquid jet in turn? (i) (ii) water tetrachloromethane charged rod liquid jet ( 2 (d) Give reasons for your predictions in (c) ( 2 83.II.B.10.b. Briefly explain the anomalous behaviour of the first compound in the following figures : ( 6

14 4 : Bonding and Structure A.L. BOSCO P I.B.6.c. (i) What do you understand by the term hydrogen bond? (ii) Ammonia can act both as a donor and as an acceptor of hydrogen bonds. Indicate by a stetch the interaction of two ammonia molecules to illustrate this fact. (iii) Water and hydrogen fluoride both form hydrogen bonds. Explain why ice floats on water while solid hydrogen fluoride does not float on its own liquid. ( 7 84.I.B.8.c. n-butane ( m.p. 138 o C ; b.p. 0.5 C ) can be readily liquefied. Liquid n-butane, supplied in steel cylinders, is used as a household fuel under the trade name LPG. (i) Why is liquid n-butane stored in steel cylinders? (ii) Explain why n-butane can be liquefied at room temperature. (iii) How are n-butane molecules arranged in the liquid state? (iv) What forces are acting between the n-butane molecules in the liquid state? ( 5 85.I.A.2.a. The boiling point of CH 4 is less than that of SiH 4. However the boiling points of NH 3 and H 2 O are greater than those of PH 3 and H 2 S respectively. Account for both of these observations. ( 4 87.I.C.1. Discuss the origin of different forces of attraction between molecules ( intermolecular forces ) and also comment on the relative strength of these forces. ( 20

15 4 : Bonding and Structure A.L. BOSCO P II.A.3.c. Arrange the following substances in order of increasing melting point : NaF, F 2, HF. Explain your order in terms of the bonding involved. ( 4 91.II.A.2.a. Arrange the following substances in order of increasing boiling points : C 2 H 5 Cl, CH 4 and C 2 H 6. Explain your order by comparing the relative magnitudes and nature of the intermolecular forces. ( 4 92.II.A.3.a. (i) Describe the bonding and intermolecular forces in ice and in SiO 2 solid. (ii) What type of interactions must be overcome to melt these solids? ( 4 94.II.A.2.b.i Account for the fact that concentrated H 3 PO 4 has a high viscosity. ( 2 88.II.A.2.c. Graphite is a macromolecular crystal. (i) Discuss the physical properties of graphite with respect to its structure. (ii) Discuss the hybridization of the electron configuration of carbon in graphite. ( 4

16 4 : Bonding and Structure A.L. BOSCO P I.A.2.b. A sulphide ion ( open circle ) has been omitted in the diagram on the right, which represents a unit-cell of zinc sulphide ( the zinc blende structure ). (i) (ii) On the diagram, add the missing sulphide ion and draw lines to show to which zinc ions ( solid circles ) this sulphide ion would be bonded. If all the zinc and sulphide ions were replaced by carbon atoms, what structure would this represent? ( 2

17 4 : Bonding and Structure A.L. BOSCO P I.B.7.c. Figure I Figure II Figure I above represents an exploded view of a model of three layers of spheres on top of one another. Layer a is in contact with layer b, and layer b is in contact with layer c. If a fourth layer is placed on layer c so that the centres of the spheres are directly above the centres of the spheres in the first layer and the model is repeated, the sequence of the layers become abcabc... (i) What type of packing does this model represent? (ii) If the sequence is changed to abab..., what type of packing would the model represent? (iii) What is the coordination number in both (i) and (ii)? A unit cell for the abcabc... arrangement is shown in Figure II. (iv) How many equivalent complete spheres can be considered to belong to the unit cell? ( 4 83.I.B.7.c.i

18 4 : Bonding and Structure A.L. BOSCO P.18 Copper is shown by X-ray analysis to crystallize in the face-centred cubic structure. How many copper atoms are present in the unit cell of this structure? ( 2 85.II.A.3.b. The following is a unit cell of an oxide of titanium : (i) What is the co-ordination number of titanium? (ii) State the number of titanium ions and oxygen ions per unit cell. Explain your answer. (iii) Write the formula of the compound. ( 5 86.II.A.2.a.

19 4 : Bonding and Structure A.L. BOSCO P.19 The figure below shows the unit cell of calcium fluoride : (i) What is the co-ordination number of calcium? (ii) Work out the unit cell contents and hence deduce the empirical formula of calcium fluroide. ( 4 87.I.A.1.c. Outline the different typical close-packing of atoms in the space lattices of metals. ( 4 88.I.A.1.c. Sodium and caesium are both group I metals in the Periodic Table. They both form ionic chlorides with the formula MCl ( where M is the metal ), with different crystal structures. (i) Describe the interactions within the crystals of the two compounds. (ii) Why do these two compounds have different crystal structures? ( 4 89.II.A.3.b. The figure below can be used to represent the unit cell of either zinc blende or diamond : Making use of this figure, describe the similarities and differences of the crystal lattice present in zinc blende and diamond. State a physical property which is common to both crystals, and explain why this is so. ( 6 95.I.A.1.c.

20 4 : Bonding and Structure A.L. BOSCO P.20 Account for the fact that the carbon-oxygen bond lengths in CO, CO 2 and CO 3 2- are 0.113, and nm respectively. ( 3 95.I.C.5. Write an essay on hydrogen bonding. ( I.C.5. Write an essay on the structures of diffferent types of solid, and the relationship between structure and physical properties of solids. ( II.A.1.a. For the hydrogenation of buta-1, 3-diene, H 2 C=CH CH=CH 2 (g) + 2 H 2 (g) CH 3 CH 2 CH 2 CH 3 (g) the expermental molar enthalpy change is 239 kj mol -1. (i) Estimate the molar enthalpy change for the above hydrogenation using the bond energy terms below : Bond Bond energy term / kj mol -1 H H 436 C H 413 C C 346 C = C 611 (ii) Explain why the estimated value differs from the experimental value. ( 4 96.II.A.2.b.

21 4 : Bonding and Structure A.L. BOSCO P.21 Briefly describe each of the following intermolecular forces and illustrate your answer with an appropriate example in each case. dipole-dipole interactions hydrogen bonding van der Waals forces ( 4 92.I.A.2.d. The arrangement of atoms in metals can be described by the close-packing of spheres. (i) Which close-packed structure does abcabcabc... describe? Indicate on the diagram below one tetrahedral hole ( marking it T ) and one octahedral hole ( marking it O ). (ii) Describe the bonding in metallic crystals. (iii) Of the three energy ranges in kj mol 1 given below : 5 to to to 1500 which is the most likely energy range for the change M (s) M (g), where M is a metal? ( 4 93.I.A.1.b.

22 4 : Bonding and Structure A.L. BOSCO P.22 For each of the following molecules, draw a three-dimensional structure and state the molecular geometry. (i) SiF 4. (ii) OF 2, ( 4 94.I.A.1.a. (i) Write an equation to represent the change related to the second electron affinity of oxygen. (ii) The first second electron affinities of oxygen are 142 kj mol 1 and kj mol 1 respectively. Explain why they have opposite signs. (iii) Explain why all the inert gases have positive first electron affinities. ( 4 94.I.A.1.b. The crystal structure of a compound A x B y can be described as a simple cubic lattice of A atoms with B atoms at the middle of all edges. (i) What is the empirical formula of this compound? (ii) What are the coordination numbers of an A atom and a B atom respectively? ( 2 94.I.A.1.c. For each of the following molecules, draw a three-dimensional structure showing the positions of the bond electron pairs and lone electron pairs ( if any ). In each case, state the molecular geometry and whether the molecule possesses a non-zero dipole moment. (i) BF 3. (ii) ClF 3 ( 4

23 4 : Bonding and Structure A.L. BOSCO P I.A.2.d. (i) Explain the term hydrogen bonding. (ii) Draw a diagram of the structure of a compound which has hydrogen bonds. Indicate the hydrogen bond(s) clearly. (iii) Explain why (I) the boiling point of CH 4 is lower than that of SiH 4, and (II) the boiling point of NH 3 is higher than that of PH 3. ( 5 95.I.A.1.c. Account for the fact that the carbon-oxygen bond lengths in CO, CO 2 and CO 2 3 are 0.113, and nm respectively. ( 3 95.I.A.2.a. Explain why phosphorus can form PCl 3 and PCl 5, while nitrogen can form only NCl 3. ( 2 95.I.A.2.d. (i) State whether the following hydrides would react with water under room temperature and atmospheric pressure. If there is a reaction, give the balanced equation. CH 4, SiH 4, H 2 S and HCl. (ii) Explain the difference in reactivity with water between CH 4 and SiH 4. (iii) Explain the difference in reactivity with water between SiH 4 and H 2 S. ( 6

24 4 : Bonding and Structure A.L. BOSCO P I.A.2.e. For each of the following species, draw a three-dimensional structure showing the bond electron pairs and lone electron pairs of the central atom. State the shape of the species in each case. (i) ICl 4. (ii) SCl 2. ( 3 95.I.c.5. Write an essay on hydrogen bonding. ( 20

Q1. The table below shows the boiling points of some hydrogen compounds formed by Group 6 elements. S H 2 O H 2. Boiling point / K

Q1. The table below shows the boiling points of some hydrogen compounds formed by Group 6 elements. H O H S H Se H Te Boiling point / K 373 1 3 71 (a) State the strongest type of intermolecular force in