3 marks total 7 marks 13 chem exam 2 section b

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3 marks Total 7 marks
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13 CHEM EXAM 2 SECTION B – continued TURN OVER Question 6 a. A natural gas-fired power station generates electricity by reacting gaseous methane (CH 4 ) with oxygen. List, in order, the energy conversions that take place in the power station during this process. 2 marks b. Less electricity is generated by burning methane in a gas power station than if the same amount of methane were used in a fuel cell. i. Give one reason for this difference. ii. State one factor that limits the widespread applications of fuel cells to generate electricity. 2 marks Total 4 marks
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CHEM EXAM 2 14 Question 7 The element antimony (Sb) has at least 29 known isotopes. Only two of these are stable isotopes that occur naturally; the other 27 isotopes are radioactive and have been made artificially. The stable isotopes are Sb (relative isotopic mass = 120.9038) and Sb (relative isotopic mass = 122.9041). The relative atomic mass of naturally occurring antimony of 121.75 has been determined using mass spectrometry. a. The flow chart below represents the sequence of operations in a mass spectrometer. Three of the stages are labelled. 1 2 ionisation 3 4 deflection 5 collection and detection i. What operations occur in stages 1 and 3? stage 1 stage 3 ii. How is ionisation achieved in stage 2? iii. How is deflection achieved in stage 4? 2 + 1 + 1 = 4 marks b. What information can be obtained from a mass spectrometer about naturally occurring antimony? 2 marks c. From the data given, calculate the percentage abundance of each of the stable isotopes of naturally occurring antimony. 3 marks SECTION B – Question 7 – continued
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15 CHEM EXAM 2 SECTION B – continued TURN OVER d. Give the symbol and charge of the most common antimony ion that would be detected using mass spectrometry.
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