Edexcel Jun 2012 Paper 1 Q21 (with explained solutions) |

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Edexcel Jun 2012 Paper 1 Q21

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SECTION B Answer ALL the questions. Write your answers in the spaces provided. 21 (a) Define the term relative isotopic mass. (2)(b) Naturally occurring chlorine contains 75.53% of 35Cl and 24.47% of 37Cl. (i) Calculate the relative atomic mass of chlorine to four significant figures. (ii) Two of the peaks in the mass spectrum of chlorine, Cl2, are at m/e 70 and 74. Identify the species giving rise to these peaks. (2) (2) 7074(iii) What is the m/e value of the other peak that you would expect to see in this region of the mass spectrum and the identity of the species giving rise to it? (2) ValueSpecies(Total for Question 21 = 8 marks) *P39306A0924* Turn over<br />

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First mark: Mass of an atom/mass of an isotope (of an element) (1) IGNORE any references to average or (weighted) mean Second mark: relative to 1/12th the mass of a 12C atom (1) NOTE: The second mark is awarded for any mention of 12C IGNORE throughout the candidates answer any references to moles or 1 mol or 12 g Mark the two points independently Acceptable Answers Question Number 21(b)(i) {(35 x 75.53) + (37 x 24.47)}100 (1) = 35.4894 = 35.49 (1) Answer to 4 s.f. only. Correct answer no working (2) IGNORE units of any kind (e.g. g g mol1 amu, etc.) Reject Mark Section B Question Number 21(a) Acceptable Answers Reject Mark Mass of (all the) isotopes /atoms Mass of an element<br />
+/(35Cl 35Cl)+ (1) +/(37Cl 37Cl)+ (1) 35Cl2 37Cl2 ALLOW (35Cl + 35Cl)+ and/or (37Cl + 37Cl)+ OR (35Cl35Cl)+ and/or (37Cl37Cl)+ OR (35Cl and 35Cl)+ and/or (37Cl and 37Cl)+ If the formal charge is omitted on either ion (or both the ions), then award (1) mark only. NOTE: 35Cl+ 35Cl+ and 37Cl+ 37Cl+ scores (1) as each ion has an extra + charge. 235Cl+ and 237Cl+ scores (1) Accept mass number written as superscript to right of symbol. + + 70Cl2 74Cl2 235Cl and/or 237Cl scores (0) Reject Mark Question Number 21(b)(ii) Acceptable Answers Reject Mark Question Number 21(b)(iii) 72 (1) Acceptable Answers 35Cl 37Cl(+) (1) ALLOW (35Cl + 37Cl)(+) and/or (37Cl + 35Cl)(+) OR (37Cl35Cl)(+) and/or (37Cl35Cl)(+) OR (35Cl and 37Cl)(+) and/or (37Cl and 35Cl)(+) NOTE: The + charge is not needed on this ion IGNORE extra + charges, so ALLOW 35Cl+ 37Cl+ and/or 37Cl+ 35Cl+<br />

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