OCR A Jan 2013 Paper 1 Q1 (with explained solutions) |

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OCR A Jan 2013 Paper 1 Q1

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Answer all the questions. Tungsten metal is used in the manufacture of some types of steel. Tungsten has an atomic number of 74. (a) Tungsten has many isotopes. (i) Explain what is meant by isotopes.[1] (ii) The mass number of one isotope of tungsten is 184. Complete the table below to show the atomic structure of this tungsten isotope. Protons Neutrons Electrons [1] (iii) What is used as the standard measurement of relative isotopic mass?[1] (b) In the manufacture of tungsten metal, an oxide of tungsten, WO3, is reacted with hydrogen gas. WO3(s) + 3H2(g) W(s) + 3H2O(g) (i) Using oxidation numbers, show what has been oxidised and what has been reduced in this reaction. oxidisedreduced[2]OCR 2013<br />
(ii) A chemist reacts 11.59 g of WO3 with hydrogen gas. Calculate the volume of hydrogen gas, in dm3, required to completely react with this mass of WO3 at room temperature and pressure. volume of hydrogen gas =dm3 [3] [Total: 8]OCR 2013 Turn over<br />

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F321 Question 1 (a) Answer (i) Atom(s) of an element AND with different numbers of neutrons (and with different masses) (cid:57) Mark Scheme January 2013 Marks Guidance ALLOW for atoms of an element: Atoms of the same element OR atoms with the same number of protons OR atoms with the same atomic number IGNORE different relative atomic masses IGNORE different mass number IGNORE same number of electrons DO NOT ALLOW different numbers of electrons DO NOT ALLOW atoms of elements for atoms of an element DO NOT ALLOW an element with different numbers of neutrons (ie atom(s) is essential) (ii) Protons 74 Neutrons 110 Electrons 74 (cid:57) (iii) 12C OR C-12 OR carbon 12 OR carbon-12 (cid:57) (b) (i) (Oxidised): H (oxidation number has increased) from H = 0 to H = +1 (cid:57) (Reduced): W (oxidation number has decreased) from W = +6 to W = 0 (cid:57) 1 1 2 IGNORE 1/12th AND amu ALLOW 6+ OR 6 OR 1+ OR 1 ALLOW one mark for correct oxidation number changes H = 0 to H = +1 AND W = +6 to W = 0 ALLOW oxidation states written above the equation if not seen in the text BUT IGNORE oxidation states written above the equation if seen in the text ALLOW for one mark: (Oxidised) H has increased by 1 AND (Reduced) W has decreased by 6 IGNORE WO3 is reduced IGNORE references to electron loss / gain if correct DO NOT ALLOW incorrect references to electron loss / gain DO NOT ALLOW H oxidised and W reduced without reference to oxidation number changes<br />
(ii) FIRST CHECK THE ANSWER ON ANSWER LINE Marks Guidance Mark Scheme January 2013 If there is an alternative answer, check to see if there is any ECF credit possible using working below ALLOW calculator value or rounding to 2 significant figures or more BUT IGNORE trailing zeroes, eg 0.200 allowed as 0.2 if wrong Mr produces such numbers throughout. IF answer = 1.2(0) dm3 award 2 marks (not multiplying by 3) ALLOW use of inexact Mr (eg 232)if it still gives 0.05 ALLOW amount of WO3 x 3 correctly calculated for 2nd mark ALLOW amount of H2 x 24.0 correctly calculated for 3rd mark ALLOW 1 mark for incorrect amount of WO3 x 24.0 (not multiplied by 3 ie scores third mark only) F321 Question 1 (b) Answer IF answer = 3.6(0) (dm3) award 3 marks Amount of WO3 = (11.59 / 231.8 = ) 0.05(00) (mol) (cid:57) Amount of H2 = 0.0500 x 3 = 0.15(0) (mol) (cid:57) Volume of H2 = 0.150 x 24.0 = 3.6(0) (dm3) (cid:57) Total<br />

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