OCR A AS Jun 2016 Paper 2 Q2 (with explained solutions) |

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OCR A AS Jun 2016 Paper 2 Q2

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The graph shows the melting points of the elements in Period 3 of the periodic table. Si 1800 1600 1400 1200 melting point 1000 / K Mg Al 800 600 400 200 Na Cl Ar 0 10 11 12 14 13 15 atomic number 16 17 18 19 (a) Phosphorus and chlorine have simple molecular structures. More information about phosphorus and chlorine is given in the table below. Element phosphorus chlorine Molecular formula P4 Cl2 Explain the differences in the melting points of phosphorus and chlorine.[3]OCR 2016<br />
(b) Magnesium and silicon have different types of giant structures. Describe the bonding in magnesium and in silicon. Include the names of the particles and describe the forces between the particles in the structures.[4] (c) Aluminium forms a sulfide, Al2S3. Al2S3 reacts with water to form aluminium hydroxide and hydrogen sulfide, H2S. Write an equation for the reaction of Al2S3 with water.[1]OCR 2016 Turn over<br />

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H032/02 Mark scheme June 2016 Question 2 (a) Phosphorus has more electronsAnswer Stronger London forces OR Stronger induced dipole(-dipole) interactionsMore energy required to break the intermolecular forces/bonds OR London forces(b) Magnesium metallic (bonds) cations/positive ions/Mg2+ AND delocalised electronsSilicon covalentbetween atoms(c) Al2S3 + 6H2O2Al(OH)3 + 3H2STotal Guidance ALLOW ORA but comparison should be used for the all marks DO NOT ALLOW Phosphorus has more electrons in the outer shell or larger electron cloud. IGNORE Phosphorus molecules are bigger or have greater Mr. ALLOW more for stronger ALLOW stronger van der Waals/vdW forces DO NOT ALLOW attraction between atoms or that covalent bonds are broken ALLOW the (electrostatic) attraction between cations/positive ions and delocalised electrons for both Mg marksDO NOT ALLOW molecules for second mark IGNORE sea of electrons ALLOW the attraction between a shared pair of electrons and the nuclei of the (bonded) atoms for both marksDO NOT ALLOW any intermolecular forces in marking points 2 and 4 or silicon molecules IGNORE state symbols ALLOW correct multiples AO element AO1.12 AO2.1 AO1.14 AO2.5 Marks 1 1 1<br />

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