OCR A Jun 2014 Paper 1 Q1 (with explained solutions) |

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OCR A Jun 2014 Paper 1 Q1

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Answer all the questions. 1 Antimony, Sb, has atomic number 51. (a) Complete the table below to show where antimony is found in the Periodic Table. Period Block PMT [1] (b) Antimony exists as a mixture of isotopes. (i) What is meant by the term isotopes?[1] (ii) Different isotopes of antimony have the same chemical properties. Explain why.[1] (iii) Complete the table below to show the atomic structure of 121Sb. Protons Neutrons Electrons [1] (c) The relative atomic mass of antimony is 121.8. (i) Define the term relative atomic mass.[3]OCR 2014<br />
(ii) A sample of antimony, Ar = 121.8, was analysed and was found to consist of 60% 121Sb and one other isotope. Determine the mass number of the other isotope in the sample of antimony. PMT mass number of the other antimony isotope =[1] (d) Antimony chloride, SbCl3, exists as simple covalent molecules. A dot-and-cross diagram of SbCl3 is shown below. Cl Sb Cl Cl (i) Predict the shape of a molecule of SbCl3. Explain your answer. name of shape:explanation:[3] (ii) SbCl3 molecules are polar. Explain why.[2] [Total: 13]OCR 2014 Turn over<br />

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Answer period = 5 AND block = p (cid:57) (i) Atom(s) of an element AND with different numbers of neutrons (and with different masses) (cid:57) (ii) same number of electrons in outer shell OR same electron configuration OR electron structure (cid:57) (iii) 51p 70n 51e (cid:57) F321 Question 1 (a) (b) (b) (b) Mark Scheme June 2014 Mark 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 number 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) IGNORE same number of protons IGNORE same number of electrons IGNORE they are the same element<br />
F321 Mark Scheme June 2014 Question 1 (c) (i) Answer The (weighted) mean mass of an atom (of an element) OR The (weighted) average mass of an atom (of an element) (cid:57) compared with 1/12th (the mass) (cid:57) of (one atom of) carbon-12 (cid:57) (c) (ii) 123 (cid:57) (d) (i) (Trigonal) Pyramidal (cid:57) (Sb has) three bonding pairs AND one lone pair of electrons (cid:57) Pairs of electrons repel (cid:57) Mark Guidance ALLOW average atomic mass DO NOT ALLOW mean mass of an element ALLOW mean mass of isotopes OR average mass of isotopes DO NOT ALLOW the singular isotope For second AND third marking points ALLOW compared with (the mass of) carbon-12 which is 12 For three marks; ALLOW mass of one mole of atoms compared to 1/12th (mass of) one mole OR 12g of carbon OR ALLOW mass of one mole of atoms . 1/12th mass of one mole OR 12g of carbon-12 ALLOW 123Sb OR Sb-123 OR antimony-123 ALLOW 123.0 IGNORE working ALLOW alternative phrases/words to repel eg push apart ALLOW lone pairs repel more than bonding pairs ALLOW bonds for bonded pairs ALLOW lp and bp IGNORE electrons repel DO NOT ALLOW atoms repel<br />
F321 Mark Scheme June 2014 (ii) There is a difference in electronegativities (between Sb Mark Guidance ALLOW Because Cl is more electronegative (than Sb) OR Because Sb is more electronegative (than Cl) ALLOW description that electrons are drawn along a covalent bond IGNORE single + or single - for dipole IGNORE diagram if M1 awarded in text ALLOW partial charges do not cancel IGNORE references to lone pair causing dipoles Question 1 (d) Answer and Cl) OR (Sb-Cl) bonds are polar OR have a dipole OR Dipoles seen on the diagram (cid:57) The molecule is not symmetrical AND dipoles do not cancel (cid:57) Total 13<br />

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