OCR A Jun 2012 Paper 1 Q1 (with explained solutions) |

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OCR A Jun 2012 Paper 1 Q1

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Answer all the questions. 1 Sulfur, atomic number 16, is found within the Earths crust. Sulfur is released into the atmosphere at times of volcanic activity. A sample of sulfur from a volcano was analysed to give the following composition of isotopes. isotope abundance (%) 32S 33S 34S 95.02 0.76 4.22 (a) Define the term relative atomic mass.[3] (b) Calculate the relative atomic mass of the sample of sulfur. Give your answer to two decimal places. answer =[2] (c) John Dalton, an early 19th century scientist, believed that elements were made up of tiny particles called atoms which could not be divided. Nowadays, chemists know of the existence of sub-atomic particles in atoms and in ions. Complete the table to show the number of sub-atomic particles in the 33S atom and 34S2 ion. protons neutrons electrons 33S2 34S2OCR 2012 [2]<br />
(d) Solid sulfur exists as a lattice of S8 molecules. Each S8 molecule is a ring of eight atoms. How many atoms of sulfur are there in 0.0120 mol of S8 molecules? answer =atoms [2] (e) The only intermolecular forces in solid sulfur are van der Waals. (i) Describe how van der Waals forces arise.[3] (ii) Suggest why there are no other intermolecular forces in solid sulfur.[1] (f) Sodium thiosulfate is a compound of sulfur used to develop photographs. Hydrated sodium thiosulfate has the formula Na2S2O35H2O. What is the oxidation number of sulfur in Na2S2O35H2O?[1]OCR 2012 Turn over<br />
(g) A student heats 12.41 g of hydrated sodium thiosulfate, Na2S2O35H2O, to remove the water of crystallisation. A white powder called anhydrous sodium thiosulfate forms. (i) What does the term anhydrous mean?[1] (ii) What is the relative formula mass of Na2S2O35H2O?[1] (iii) Calculate the expected mass of anhydrous sodium thiosulfate that forms. mass =g [2] (h) Sulfur hexafluoride, SF6, exists as non-polar covalent molecules with an octahedral shape. (i) Explain why a molecule of SF6 has an octahedral shape.[2] (ii) Fluorine has a higher electronegativity than sulfur, yet SF6 molecules are non-polar. Explain what is meant by the term electronegativity and suggest why SF6 molecules are non-polar.[3] [Total: 23]OCR 2012<br />
BLANK PAGE PLEASE DO NOT WRITE ON THIS PAGE TURN OVER FOR QUESTION 2OCR 2012 Turn over<br />

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F321 Question 1 (a) (b) Mark Scheme June 2012 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) FIRST CHECK THE ANSWER ON THE ANSWER LINE If answer = 32.09 award 2 marks 3295.02 + 330.76 + 344.22 100 OR 30.4064 + 0.2508 + 1.4348 OR = 32.092 (calculator value) (cid:57) (Ar =) 32.09 (cid:57) Marks 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 ALLOW mass of one mole of atoms (cid:57) compared to 1/12th (cid:57) (mass of) one mole OR 12g of carbon-12 (cid:57) ALLOW mass of one mole of atoms . 1/12th mass of one mole OR 12g of carbon-12 ALLOW one mark for ECF from transcription error in first sum provided final answer is to 2 decimal places and is between 32 and 34 and is a correct calculation of the transcription Answer must be 2 decimal places<br />
Mark Scheme June 2012 Answer Marks Guidance F321 Question 1 (c) (d) 2 2 Mark by row If there is an alternative answer, check to see if there is any ECF credit possible using working below ALLOW 5.8 x 1022 up to calculator value of 5.7792 x 1022 ALLOW correct rounding of ECF to 2 significant figures or more up to calculator value ALLOW answers in non standard form such as 0.5781023 correctly rounded to 2 or more significant figures Use annotations with ticks, crosses, ECF etc for this part ALLOW movement of electrons ALLOW changing electron density ALLOW transient, oscillating momentary changing DO NOT ALLOW induces a temporary dipole for the second marking point ALLOW induces a dipole in neighbouring molecules ALLOW causes a resultant dipole in other molecules ALLOW atoms for molecules 33S 34S2 (cid:57) (cid:57) 16 18 17 18 16 16 protons neutrons electrons FIRST CHECK THE ANSWER ON THE ANSWER LINE If answer = 5.781022 award 2 marks (mol of atoms) = 0.01208 = 0.0960 (mol) OR (no. of molecules) = 0.01206.021023 = 7.224 x 1021 OR (no. of S atoms in 1 mole of S8) = 8 x 6.02 x 1023 = 4.816 x 1024(cid:57) Correctly calculates (number of atoms) = 0.012086.021023 = 5.781022 (atoms) (cid:57) (e) (i) Creating the dipole mark Uneven distribution of electrons (cid:57) Type of dipole mark Creates or causes an instantaneous dipole OR temporary dipole (in a molecule) (cid:57) Induction of a second dipole mark Causes induced dipoles in neighbouring molecules (cid:57)<br />
F321 Mark Scheme June 2012 Question (e) (ii) Only one type of atom Answer OR No (permanent) dipoles OR non-polar OR no polar bonds (cid:57) + 2 (cid:57) There are no waters of crystallisation (cid:57) (f) (g) (i) (ii) 248.2 (cid:57) (iii) FIRST CHECK THE ANSWER ON THE ANSWER LINE If answer = 7.91 (g) award 2 marks (amount of Na2S2O35H2O) = 12.41/248.2 OR = 0.05(00) (mol) (cid:57) (mass of Na2S2O3) = 0.05 x 158.2 = 7.91 (g) (cid:57) Marks Guidance ALLOW no difference in electronegativity IGNORE No hydrogen bonding IGNORE No lone pairs ALLOW 2(+) ALLOW without water no water etc IGNORE dehydrated IGNORE units DO NOT ALLOW 248 If there is an alternative answer, check to see if there is any ECF credit possible using working below ALLOW ECFs from answer to (g)(ii) for both marking points ALLOW ECF for calculated mol of Na2S2O35H2O x 158.2 correctly calculated for the 2nd mark ALLOW calculator value or rounding to 3 significant figures or more but IGNORE trailing zeroes, eg 0.200 allowed as 0.2<br />
June 2012 Guidance ALLOW It has six bonded pairs ALLOW bonds for bonded pairs IGNORE regions OR areas of negative charge ALLOW bonds repel DO NOT ALLOW Atoms repel or electrons repel Lone pairs repel more than bonded pairs would score the second mark but would contradict the first mark if there is no reference to no lone pairs ALLOW dipoles cancel out IGNORE polar bonds repel IGNORE charges cancel F321 Question Answer (h) (i) Sulfur has six bonded pairs (and no lone pairs) (cid:57) Electron pairs repel (one another equally) (cid:57) Mark Scheme Marks (ii) The ability of an atom to attract electrons (cid:57) in a (covalent) bond (cid:57) (The octahedral shape) is symmetrical (cid:57) Total 23<br />

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