Candidate Name Centre Number 2 Candidate Number GCE AS/A level 331/01 CHEMISTRY CH1 A.M. WEDNESDAY, 4 June 2008 1 1 2 hours ADDITIONAL MATERIALS In addition to this examination paper, you will need a: calculator; copy of the Periodic Table supplied by WJEC. Refer to it for any relative atomic masses you require. INSTRUCTIONS TO CANDIDATES Write your name, centre number and candidate number in the spaces at the top of this page. Section A Answer all questions in the spaces provided. Section B Answer all questions in the spaces provided. FOR EXAMINER S USE ONLY Section Question A B 1-7 8 9 10 11 TOTAL MARK Mark Candidates are advised to allocate their time appropriately between Section A (10 marks) and Section B (56 marks). INFORMATION FOR CANDIDATES The number of marks is given in brackets at the end of each question or part-question. The maximum mark for this paper is 66. Your answers must be relevant and must make full use of the information given to be awarded full marks for a question. You are reminded that marking will take into account the Quality of Written Communication used in all written answers. Page 16 may be used for rough work. CJ*(S08-)
2 Examiner SECTION A Answer all the questions in the spaces provided. 1. State the number of protons in a Ca 2+ ion. [1]............................................................................................................. 2. The diagram shows the ionisation energies to successively remove all eleven electrons from a sodium atom. Complete the graph by filling in, with dots, the missing points for removing the second and tenth electrons and connecting them to their neighbouring points. 6 5 lg ionisation energy /kj mol 1 4 3 2 1 2 3 4 5 6 7 8 9 10 11 number of electrons removed [2] 3. State which of the following solids is represented by the diagram below: A caesium chloride; B diamond; C iodine; D silicon dioxide. [1]................................................................................... (331/01)
3 Examiner 4. (a) Define the mole. [1] (b) State which one of the following is the number of moles of aluminium ions, Al 3+, in 0 30 moles of aluminium oxide, Al 2 O 3 : A 0 10; B 0 15; C 0 60; D 0 90. [1]................................................................................... 5. State which one of the following letters represents the weakest type of bonding: A covalent; B hydrogen; C ionic; D metallic. [1]................................................................................... 6. Describe the shape of a p-orbital. [1] Turn over.
4 Examiner 7. (a) Explain the term electronegativity. [1] (b) The table gives some electronegativity values. Atom A1 Be H Mg N S Electronegativity 1 61 1 57 2 20 1 31 3 04 2 59 Select the two atoms from the list which would give the most polar bond when combined. [1] Section A Total [10]
5 BLANK PAGE Turn over.
6 Examiner SECTION B Answer all the questions in the spaces provided. 8. In November 2006 a Russian, Alexander Litvinenko, was killed in London, apparently as a result of poisoning by a radioactive isotope of polonium, 210 Po. (a) (i) 210 Po is manufactured in small amounts by bombarding 209 Bi with neutrons. 209 Bi + 1 n 210 Po + X Identify the product X. [1] (ii) 210 Po decays by α-emission. Give the mass number and symbol of the isotope formed when 210 Po decays by α-emission. [1] Mass number............................................................... Symbol................................................................... (iii) 210 Po decays with a half life of 138 days and the maximum safe level in the body is thought to be 7 picograms. If a sample of water is contaminated with 56 picograms of 210 Po, calculate the minimum time that must elapse before the sample of water reaches the maximum safe level of 210 Po. [2] (iv) It is suspected the 210 Po was smuggled into London in a small glass container carried in luggage. Explain why there is relatively little risk due to radioactivity when the polonium is in luggage but it is lethal once taken into the body in food or drink. [2] (b) Polonium forms a chloride, PoCl 4, which is a yellow solid, volatile above 150 C and soluble in non-polar solvents. State the type of bonding present in PoCl 4. [1]
7 Examiner (c) When a sample of 210 PoCl 4 was passed through a mass spectrometer, the spectrum showed five molecular ion peaks corresponding to masses 350, 352, 354, 356 and 358. (i) State the two isotopes of Cl found in naturally occurring chlorine. [1] (ii) Each of the five molecular ions giving peaks in the mass spectrum of 210 Po chloride, 210 PoCl 4, contains one 210 Po atom and four Cl atoms. Using your answer to (i), state how many atoms of each of the two Cl isotopes are present in each molecular ion. [2] 350 molecular ion................................................................................................................................................... 352 molecular ion................................................................................................................................................... 354 molecular ion................................................................................................................................................... 356 molecular ion................................................................................................................................................... 358 molecular ion................................................................................................................................................... (iii) Explain how the positive ions produced in a mass spectrometer are formed and separated. [3] Total [13] Turn over.
8 Examiner 9. (a) The table shows some of the elements in the Periodic Table together with the melting temperature of the most important solid form of the element. I II III IV V VI VII 0 Element C (diamond) Ne Melting temperature / K 3900 25 Element Na Mg Al Si P S Cl Ar Melting temperature / K 371 922 933 1683 317 392 172 84 (i) State which of the elements shown will not be solids at room temperature. [1] (ii) Explain, in terms of bonding and structure, why silicon, Si, and carbon, C, have the highest melting temperatures. [2] (iii) Explain why neon, Ne, and argon, Ar, have the lowest melting temperatures. [2]
9 Examiner (iv) Explain why the melting temperature increases for the sequence Na, Mg, Al, even though all three involve metallic bonding. [2] (v) Explain why the melting temperature for Si is lower than that for C even though they involve the same bonding and structure. [1] (vi) Explain why the melting temperature of argon, Ar, is higher than that for neon, Ne. [1] Turn over.
10 Examiner (b) Another form of carbon is graphite. Describe the bonding and structure of graphite. Your answer should include the different types of bonding present the arrangement of atoms how the bonding affects the electrical conductivity and other physical properties. [4] Total [13]
11 BLANK PAGE Turn over.
12 Examiner 10. Crystalline barium hydroxide exists as a hydrate, Ba(OH) 2.xH 2 O, which dissolves in water. (a) Explain the interactions between ions and water molecules. [3] (b) Name a test, and the expected result, which could be used to show the presence of barium ions in the hydrate crystals. [1] (c) The molar mass of barium hydroxide hydrate, Ba(OH) 2.xH 2 O, is 315 46 g mol 1. (i) After removal of all the water molecules, the molar mass drops to 171 30 g mol 1. Calculate the value of x in the formula Ba(OH) 2.xH 2 O. [2] (ii) Barium hydroxide hydrate has a solubility of 5 60g per 100cm 3 water at room temperature. Calculate, to three significant figures, the solubility of barium hydroxide in mol dm 3. [2] (iii) Giving your reason(s), state whether calcium hydroxide will have a higher or lower solubility than barium hydroxide. [1]
13 Examiner (d) (i) Explain the term oxidising agent. [1] (ii) State, giving a reason, whether chlorine, Cl 2, is a stronger or weaker oxidising agent than bromine, Br 2. [1] (iii) Write an equation for the reaction of chlorine with water and, by allocating oxidation numbers, explain why this reaction is a redox reaction. [3] (iv) Outline a test, and the expected observations, to show the presence of chloride ions, Cl, in an aqueous solution. [2] Total [16] Turn over.
14 Examiner 11. This question is concerned with some compounds of phosphorus, P, atomic number 15. (a) State the full electron sub-shell configuration for an atom of phosphorus. [1] (b) The molecular formula of phosphorus(v) oxide is P 4 O 10. (i) State the empirical formula of phosphorus(v) oxide. [1] (ii) State the bonding and structural type present in solid P 4 O 10. [1] (c) Phosphorus(V) oxide is used as a desiccating agent to remove water because of the reaction shown below. P 4 O 10 + 6H 2 O 4H 3 PO 4 (i) Calculate the molar mass (g mol 1 ) of phosphorus(v) oxide. [1] (ii) Calculate the maximum mass of water which can be removed by reacting with 28 4g of phosphorus(v) oxide. [2] (d) Phosphoric(V) acid, H 3 PO 4, produced when phosphorus(v) oxide reacts with water, is an important chemical with uses ranging widely from cola drinks to rust remover. Its salts, such as calcium phosphate, are also important. (i) Write the formula for calcium phosphate. [1] (ii) Give one example of the importance of calcium phosphate. [1]
15 Examiner (e) Phosphorus forms two chlorides, phosphorus(v) chloride, PCl 5 and phosphorus(iii) chloride, PCl 3. (i) Draw a dot and cross diagram to show the bonding in phosphorus(iii) chloride, PCl 3, and use this diagram to explain the term lone pair of electrons. [2] Diagram Lone pair of electrons................................................................................................................................................................................................................................................................................................................................................ (ii) Show, either by a diagram or by naming, the shapes of gaseous PCl 5 and PCl 3 molecules. [2] PCl 5 PCl 3 shape shape (iii) PCl 3 reacts with aluminium chloride to form a compound Cl Cl Cl P A1 Cl Cl Cl Explain the significance of the arrow in this structure. [2] Total [14] Section B Total [56] Turn over.
16 Examiner Rough work...................................................................................................................................................................................................................................................................................
CHEMISTRY CH1 Section A 1. 20 protons. [1] 2. 2nd electron in line with other second shell electrons (1) 10 th electron similar value to 11 th electron (1) [2] 3. C iodine [1] 4. (a) The mole is the amount of material which contains the same number of particles as there are atoms in 12 g of 12 C isotope. [1] (b) C 0.60 [1] 5. B hydrogen [1] 1
6. Dumbbell shape or appropriate diagram [1] 7. (a) Electronegativity is the ability of an atom to attract electrons within a (covalent) bond [1] (b) Mg and N [1] Section A Total [10] 2
Section B 8. (a) (i) X is an electron / β particle [1] (ii) Mass number 206 Symbol Pb 2 (½) [1] (iii) 56 28 14 7 picograms so 3 half-lives (1) 3 138 = 414 days (1) [2] (2 marks for correct answer with no working) (iv) α - particles (have low penetrating power and) are stopped by glass / air / luggage. (1) but when ingested they cause damage by direct contact with organs etc. (1) [2] (b) PoCl 4 will involve covalent bonding [1] (c) (i) 35 Cl and 37 Cl 2 (½) [1] (ii) 350 [ 210 Po 35 Cl 4 ] + 352 [ 210 Po 35 Cl 37 3 Cl] + 354 [ 210 Po 35 Cl 37 2 Cl 2 ] + 356 [ 210 Po 35 Cl 37 Cl 3 ] + 358 [ 210 Po 37 Cl 4 ] + All 5 correct - 2 marks 3 correct - (1) (Allow 1 consequential mark if (c)(i) isotopes are wrong but candidate shows correct formulation of the molecular ions.) [2] (iii) Ions formed by electron bombardment (1) Ions accelerated and/or collimated by charged plates/electric field (1) Ions passed through a (curved) (electro)magnetic field (1) Ions deflected according to their mass / charge ratio (1) ((½) if mass mentioned) (any three) (Marks can be obtained by appropriate labelled diagram) [3] Total [13] 3
9. (a) (i) Cl, Ne, Ar (1) for three, (½) for two. Treat more than three answers as "right wrong" [1] (ii) (Only) covalent (½) giant lattice / macromolecular structures (½). Must break strong bonds, requiring considerable energy for melting (1) [2] (iii) (Monatomic) species with van der Waals forces between atoms (1) Weak interatomic forces require little energy to break (1) [2] (iv) Na, Mg, Al have respectively 1, 2 and 3 outer electrons (1) so more electrons involved in the electron sea / delocalised electrons resulting in stronger bonds. (1) [2] (v) Covalent bonds become weaker going down a group / C-C bonds stronger than Si-Si [1] (vi) Atoms become larger/have more electrons going down a group so there are more/stronger van der Waals forces. [1] (b) Q9(b) is to be assessed for Quality of Written Communication. [L] [4] Candidates must satisfy the following criteria Selection of a form and style of writing appropriate to the question Organisation of the relevant information clearly and coherently Use of legible text with adequate spelling, punctuation and grammar. Any 8 (½) layered structure / macromolecular stucture covalent bonding within layers interlinked / fused hexagons within layers delocalised electrons within layers sideways overlap of p-orbitals produces delocalisation van der Waals forces between layers / weak forces between layers bonding within layers much stronger than bonding between layers electrical conductivity (within layers) due to delocalized electrons no / negligible electrical conductivity from one layer to another crystals weak along the layer planes / layers easily slip over one another crystals strong at right angles to the layers high melting temperature due to strong covalent bonds low solubility due to strong covalent bonds (Marks can be obtained by appropriate labeled diagrams) Total [13] 4
10. (a) Large difference in electronegativities between O and H / water has bond dipoles / is a polar molecule (½) H δ+ O δ on both covalent bonds in water (½) O δ attracted to (Ba 2+ ) cation (1) H δ+ attracted to (OH ) anion (1) [3] (b) Flame test (½) (Apple / light ) green flame produced (½ ) or Dissolve in water and add dilute sulphuric acid (½) White precipitate formed (½) [1] (c) (i) 315.46 171.30 = 144.16 (1) 144.16 / 18.02 = 8 so x = 8 (1) (2 marks for correct answer with no working) [2] (ii) 5.60 / 315.36 = 0.0177(6) mol (1) so concentration = 0.0177(6) 1000 / 100 = 0.178 mol dm -3 (1) [2] (iii) Calcium hydroxide will have a lower solubility than barium hydroxide as the Group II hydroxides increase in solubility down the group. [1] (d) (i) An oxidizing agent accepts electrons (hence oxidizing another species). [1] (ii) Chlorine, Cl 2, is a stronger oxidizing agent than bromine, Br 2, as it has a stronger attraction for electrons / greater electronegativity / oxidising power decreases down Group VII. [1] (iii) 2Cl 2 + 2H 2 O = 4HCl + O 2 (1) 0 +1-2 +1-1 0 Cl is reduced / accepts electron as Ox No decreases (1) O is oxidized as Ox No increases. (1) (must have before and after ox. nos correct) [3] or Cl 2 + H 2 O = HCl + HClO (1) 0 +1-2 +1-1 +1 +1-2 One Cl atom reduced (1) The other Cl atom oxidized (1) (must have before and after Cl ox. nos correct) [3] (iv) 2 (1) Add silver nitrate (solution) white precipitate formed / ppt soluble in dilute ammonia [2] Total [16] 5
11. (a) 1s 2 2s 2 2p 6 3s 2 3p 3. [1] (b) (i) P 2 O 5 [1] (ii) Covalent (½) discrete molecules (½) [1] (c) (i) 284 g mol-1 [1] (ii) No moles P 4 O 10 = 28.4 / 284 = 0.100 (½) No moles water = 0.100 6 = 0.600 (½) Mass water = 0.600 18.02 = 10.8 g (1) [2] (d) (i) Ca 3 (PO 4 ) 2 [1] (ii) (Main constituent of) skeletons / bones. [1] (e) (i) o o o o o o xx P o o oo oo oo o o oo (1) Lone pair: 2 electrons in the outer shell not involved in bonding (1) [2] (ii) PCl5 trigonal bipyramid (1) PCl3 pyramidal (1) [2] (Allow unambiguous diagrams) (iii) Dative covalent / co-ordinate bond (1) Lone pair on P used to form a bond to Al (1) [2] Total [14] Section B Total [56] 6