OCR A Jan 2009 Paper 1 Q1 (with explained solutions) |

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OCR A Jan 2009 Paper 1 Q1

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Answer all the questions. 1 Carbon occurs in a wide range of compounds and is essential to living systems. (a) Two isotopes of carbon are 12C and 13C. (i) State what is meant by the term isotopes.[1] (ii) Isotopes of carbon have the same chemical properties. Explain why.[1] (iii) The 12C isotope is used as the standard measurement of relative masses. Define the term relative isotopic mass.[2]OCR 2009<br />
(b) One form of naturally occurring carbon is graphite. The table below lists some properties of graphite. electrical conductivity good conductor hardness melting point soft very highDescribe the bonding and structure in graphite. Explain, in terms of bonding and structure, the properties of graphite shown above. In your answer, you should use appropriate technical terms, spelt correctly.[5]OCR 2009 Turn over<br />
(c) In the sixteenth century, a large deposit of graphite was discovered in the Lake District. People at the time thought that the graphite was a form of lead. Nowadays, graphite is used in pencils but it is still referred to as pencil lead. A student decided to investigate the number of carbon atoms in a pencil lead. He found that the mass of the pencil lead was 0.321 g. (i) Calculate the amount, in mol, of carbon atoms in the students pencil lead. Assume that the pencil lead is pure graphite. (ii) Using the Avogadro constant, NA, calculate the number of carbon atoms in the students pencil lead. answer =mol [1] number of carbon atoms =[1] [Total: 11]OCR 2009<br />

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$F321 F321 Question 1 a i Expected Answers (atoms of the) same element OR same atomic no. OR no. of protons AND with different numbers of neutrons OR different masses(cid:57) Marks ii same (number of) electrons (in the outer shell) OR same electron configuration OR structure (cid:57) iii mass of the isotope compared to 1/12th OR mass of the atom compared to 1/12th (cid:57) (the mass of a) carbon-12 OR 12C (atom) (cid:57) Mark Scheme January 2009 Additional Guidance IGNORE same number of electrons DO NOT ALLOW different numbers of electrons DO NOT ALLOW different relative atomic masses DO NOT ALLOW elements with different numbers of neutrons without mention of same protons OR same atomic number DO NOT ALLOW different number of protons IGNORE same number of protons IGNORE they are both carbon OR they are both the same element IGNORE reference to average OR weighted mean (i.e. correct definition of relative atomic mass will score both marks) ALLOW mass of a mole of the isotope/atom with 1/12th the mass of a mole OR 12 g of (cid:57) carbon-12 (cid:57) ALLOW 2 marks for: mass of the isotope OR mass of the atom compared to 12C atom given a mass of 12.0 i.e. given a mass of 12 communicates the same idea as 1/12th.<br /> F321 Question Expected Answers Mark Scheme Marks Additional Guidance January 2009 ALLOW 12C OR C12 ALLOW FOR 2 MARKS: isotope the of mass 1/12th of mass of mass carbon 12- giant covalent (lattice) (cid:57) layers (cid:57) Each of the three properties below must be linked to explanation good conductor - because it has mobile electrons OR delocalised electrons OR electrons can move (cid:57) high melting / boiling point - because strong OR covalent bonds have to be broken (cid:57) soft - because there are van der Waals forces OR i.e. fraction is equivalent to compared to ALLOW 1 MARK FOR a mix of mass of atom and mass of mole of atoms, i.e.: mass of the isotope/mass of an atom compared with 1/12th the mass of a mole OR 12 g of carbon-12. Use annotations with ticks, crosses etc. for this part. All five marking points are independent ALLOW giant atomic OR giant molecular OR macromolecular ALLOW planes OR sheets Allow diagram showing at least two layers Electron(s) must be spelt correctly ONCE DO NOT ALLOW strong ionic bonds OR strong metallic bonds.<br /> F321 Question Expected Answers intermolecular forces OR weak bonds OR weak forces between the layers OR soft - because layers can slide (cid:57) i 0.0268 OR 0.027 OR 0.02675 mol (cid:57) Mark Scheme Marks Additional Guidance January 2009 ii 1.61 x 1022 (cid:57) Total 11 NO OTHER ACCEPTABLE ANSWER ALLOW 1.6 x 1022 up to calculator value ALLOW ECF answer to (i)6.02 x 1023 ALLOW any value for NA in the range: 6.0 x 10236.1 x 1023<br />$

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