Edexcel Jun 2016 (IAL) Paper 1 Q (with explained solutions) |

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Edexcel Jun 2016 (IAL) Paper 1 Q

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SECTION B Answer ALL the questions. Write your answers in the spaces provided. 17 A mass spectrometer can be used to measure relative isotopic masses. (a) State the meaning of the term isotopes. (1)D O N O T W R I T E I N T H I S A R E A (b) (i) In a mass spectrometer, a sample of the vapour of an element is ionized. State how this ionization is carried out. (1)(ii) Complete the equation showing the simplest ionization of a vaporised element M. M(g) (cid:111) (iii) How are the ions accelerated in the mass spectrometer? (1) (1)(iv) Ions with the same charge and travelling with the same velocity are then passed through a magnetic field. (1) magnetic field path of ions detector The path of one ion is shown. Add a line to the diagram to show the path of a lighter ion as it passes through the magnetic field and travels to the detector. *P46662A0820* D O N O T W R I T E I N T H I S A R E A D O N O T W R I T E I N T H I S A R E A<br />
A E R A S I H T N I E T I R W T O N O D A E R A S I H T N I E T I R W T O N O D A E R A S I H T N I E T I R W T O N O D (c) A sample of silicon is analysed in a mass spectrometer. Relative isotopic mass Relative abundance 28 29 30 9217 471 312 Calculate the relative atomic mass of silicon, showing your working. Give your answer to four significant figures. (d) A high resolution mass spectrometer measures masses to four decimal places. The relative molecular mass of a compound is found to be 84.0581. The relative atomic mass of an oxygen atom, 16O, is 15.9949 The relative atomic mass of a hydrogen atom, 1H, is 1.0079 Use these data to deduce whether the compound is C6H12 or C5H8O. Show your working, and state the assumption you make. (2) (3) Assumption*P46662A0920* Turn over<br />
(e) A helium mass spectrometer is an instrument used to detect leaks in containers. A sealed container filled with helium is placed in a vacuum chamber. Any helium leaking out of the container is detected by the mass spectrometer. Suggest one reason that makes helium suitable for this purpose, other than its lack of reactivity. (1)(Total for Question 17 = 11 marks) 10 *P46662A01020* D O N O T W R I T E I N T H I S A R E A D O N O T W R I T E I N T H I S A R E A D O N O T W R I T E I N T H I S A R E A<br />

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Section B Question Number 17(a) Mark (1) Acceptable Answers Reject Molecule for atom Atomic mass number Atoms of the same element / atomic number / proton number and different mass number / neutron number / nucleon number ALLOW Elements / they / isotopes have the same atomic number etc Atomic mass for mass number IGNORE references to electrons Reject Mark (1) Acceptable Answers Question Number 17(b)(i) High energy/fast moving/high speed electrons hit atoms/molecules/elements/sample (and knock electrons out.) ALLOW (Use) an electron gun/beam/stream Bombard with electrons IGNORE References to ionizing / forming (positive) ions Just an equation, e.g., M(g)M+(g) + e<br />
Reject Mark (1) Mark (1) Reject (Electro)magnetic field Positively charged plates Charged slits Acceptable Answers Question Number 17(b)(ii) M(g) + eM+(g) + 2eM+(g) ALLOW M(g)M+(g) + e M(g)e ALLOW Use of Mg+(g) for M+(g) IGNORE omission of minus sign on electron state symbol on electron Rewritten M(g) on LHS Leading 1 before any charges e.g. M(g)1+ Acceptable Answers Question Number 17(b)(iii) (With an) electric field / (negatively) charged plates (with slits in them) ALLOW Oppositely/alternatively charged plates IGNORE Electric plates<br />
Acceptable Answers Question Number 17(b)(iv) Curved path showing lighter ion deflected more ALLOW dotted line additional parallel path entering the magnet with correct deflection lines that do not reach but would extrapolate to detector on left of original beam Reject Mark (1) Straight line Lines originating from the magnet Lines deflected before passing through the magnet Lines which would not hit the detector Mark (2) Acceptable Answers Reject Answers not to 4sf (second mark) ((28x92.17) + (29x4.71) + (30x3.12)) (1) 100 (= 28.1095) = 28.11 (1) Final answer without working scores (2) IGNORE units Question Number 17(c)<br />
Mark (3) Reject Just use of C = 12 without indicating as an assumption Acceptable Answers MP2 cannot be awarded without any attempt to do a calculation for MP1 MP1 (6x12 + 12x1.0079) = 84.0948 OR (5x12 + 8x1.0079 + 15.9949) = 84.0581 (1) MP2 So mass matches for C5H8O / doesnt match for C6H12 (1) OR MP1 Mass of 12H =12.0948 (1) MP2 Remaining mass = 71.9633, so not exactly equal to 6C (1) OR MP1 Mass of H8O = 24.0581 (1) MP2 Remaining mass = 60.0000 so exactly equal to 5C (1) MP3 Assumption: (one atom of) C=12(.0000) / has mass (exactly) 12 ALLOW Other isotopes of H and/or O are not present (1) IGNORE Any units in calculations Question Number 17(d)<br />
Acceptable Answers Reject Mark Small molecule (1) Small atomic radius / small atom ALLOW Diffuses easily Not (significantly) present in air/ low density / less dense than air Non-toxic IGNORE Low mass / lighter than air / light(weight) / references to inertness or non-flammability / availability / gas at room temperature / monatomic / no isotopes / answers relating to cost (Total for question 17 = 11 marks) Question Number 17(e)<br />

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