OCR A Jun 2012 Paper 1 Q1

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Answer all the questions. 1 Sulfur, atomic number 16, is found within the Earths crust. Sulfur is released into the atmosphere at times of volcanic activity. A sample of sulfur from a volcano was analysed to give the following composition of isotopes. isotope abundance (%) 32S 33S 34S 95.02 0.76 4.22 (a) Define the term relative atomic mass.[3] (b) Calculate the relative atomic mass of the sample of sulfur. Give your answer to two decimal places. answer =[2] (c) John Dalton, an early 19th century scientist, believed that elements were made up of tiny particles called atoms which could not be divided. Nowadays, chemists know of the existence of sub-atomic particles in atoms and in ions. Complete the table to show the number of sub-atomic particles in the 33S atom and 34S2 ion. protons neutrons electrons 33S2 34S2OCR 2012 [2]<br />
 (d) Solid sulfur exists as a lattice of S8 molecules. Each S8 molecule is a ring of eight atoms. How many atoms of sulfur are there in 0.0120 mol of S8 molecules? answer =atoms [2] (e) The only intermolecular forces in solid sulfur are van der Waals. (i) Describe how van der Waals forces arise.[3] (ii) Suggest why there are no other intermolecular forces in solid sulfur.[1] (f) Sodium thiosulfate is a compound of sulfur used to develop photographs. Hydrated sodium thiosulfate has the formula Na2S2O35H2O. What is the oxidation number of sulfur in Na2S2O35H2O?[1]OCR 2012 Turn over<br />
 (g) A student heats 12.41 g of hydrated sodium thiosulfate, Na2S2O35H2O, to remove the water of crystallisation. A white powder called anhydrous sodium thiosulfate forms. (i) What does the term anhydrous mean?[1] (ii) What is the relative formula mass of Na2S2O35H2O?[1] (iii) Calculate the expected mass of anhydrous sodium thiosulfate that forms. mass =g [2] (h) Sulfur hexafluoride, SF6, exists as non-polar covalent molecules with an octahedral shape. (i) Explain why a molecule of SF6 has an octahedral shape.[2] (ii) Fluorine has a higher electronegativity than sulfur, yet SF6 molecules are non-polar. Explain what is meant by the term electronegativity and suggest why SF6 molecules are non-polar.[3] [Total: 23]OCR 2012<br />

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