Skip to content
OCR A Jan 2013 Paper 1 Q5
Answers available below
Show answer
Question
1
2
3
4
5
![5 Hydrogen chloride is a colourless gas which forms white fumes in moist air. 10 (a) Molecules of hydrogen chloride, HCl, and molecules of fluorine, F2, contain the same number of electrons. Hydrogen chloride boils at 85 C and fluorine boils at 188 C. Explain why there is a difference in the boiling points of HCl and F2. In your answer you should refer to the types of force acting between molecules and the relative strength of the forces between the molecules. In your answer, you should use appropriate technical terms, spelled correctly.[4] (b) Hydrogen chloride reacts with water to produce an ion with the formula H3O+. An H3O+ ion has one dative covalent bond. Draw a dot-and-cross diagram to show the bonding in H3O+. Show outer electrons only.OCR 2013 [2]<br />
11 (c) Borax, Na2B4O710H2O, can be used to determine the concentration of acids such as dilute hydrochloric acid. A student prepares 250 cm3 of a 0.0800 mol dm3 solution of borax in water in a volumetric flask. Calculate the mass of borax crystals, Na2B4O710H2O, needed to make up 250 cm3 of 0.0800 mol dm3 solution. answer =g [3] Question 5 continues on page 12OCR 2013 Turn over<br />
(d) The student found that 22.50 cm3 of 0.0800 mol dm3 Na2B4O7 reacted with 25.00 cm3 of dilute hydrochloric acid. 12 Na2B4O7 + 2HCl + 5H2O 2NaCl + 4H3BO3 (i) Calculate the amount, in mol, of Na2B4O7 used. (ii) Calculate the amount, in mol, of HCl used. amount =mol [1] (iii) Calculate the concentration, in mol dm3, of the HCl. amount =mol [1] concentration =mol dm3 [1] [Total: 12] END OF QUESTION PAPER Copyright Information OCR is committed to seeking permission to reproduce all third-party content that it uses in its assessment materials. OCR has attempted to identify and contact all copyright holders whose work is used in this paper. To avoid the issue of disclosure of answer-related information to candidates, all copyright acknowledgements are reproduced in the OCR Copyright Acknowledgements Booklet. This is produced for each series of examinations and is freely available to download from our public website (www.ocr.org.uk) after the live examination series. If OCR has unwittingly failed to correctly acknowledge or clear any third-party content in this assessment material, OCR will be happy to correct its mistake at the earliest possible opportunity. For queries or further information please contact the Copyright Team, First Floor, 9 Hills Road, Cambridge CB2 1GE. OCR is part of the Cambridge Assessment Group; Cambridge Assessment is the brand name of University of Cambridge Local Examinations Syndicate (UCLES), which is itself a department of the University of Cambridge.OCR 2013<br />](https://learnah.org/wp-content/uploads/2018/08/OCR_1_QP_JAN13_question_5-0.jpg)
![F321 Mark Scheme January 2013 Question 5 (a) Answer F2 forces mark F2 has van der Waals (forces) OR F2 has induced dipole attractions OR interactions OR F2 has temporary OR instantaneous dipole(dipole) attraction OR interactions (cid:57) HCl forces mark HCl has permanent dipole(dipole) attractions OR interactions (cid:57) Comparison of strength of forces between molecules mark intermolecular force in HCl is stronger than that in F2 OR permanent dipoles are stronger (than induced dipoles) (cid:57) Boiling point mark more energy is required to break stronger (intermolecular) forces (cid:57) 15 Marks Guidance Use annotations ie ticks crosses ECF ^ etc for this part ALLOW vdWs for van der Waals IGNORE F2 has covalent bond for this mark IGNORE F2 has intermolecular forces Quality of written communication: dipole(s) spelled correctly and used in context for the second marking point IGNORE HCl has intermolecular forces IGNORE van der Waals forces in HCl DO NOT ALLOW hydrogen bonding DO NOT ALLOW ionic bonding Look for strength of force comparison anywhere in the answer ALLOW ECF for hydrogen bonding in HCl being stronger than the stated intermolecular forces in F2 BUT DO NOT ALLOW this mark if HCl or F2 has covalent bonds broken OR if HCl has ionic bonds broken (the question asks for forces between molecules) IGNORE HCl has stronger van der Waals (forces) than F2 (as they both have the same number of electrons) DO NOT ALLOW fourth mark if covalent bonds are broken in HCl or F2 OR if ionic bonds are broken in HCl IGNORE heat but ALLOW heat energy<br />
Mark Scheme January 2013 Marks Guidance Must be dot-and-cross Must be H3O for either mark Circles for shells not needed IGNORE inner shells IGNORE lack of positive charge and square brackets DO NOT ALLOW second marking point if negative charge is shown on the ion Non-bonding electrons do not have to be seen as a pair ALLOW second mark for one non-bonding pair of electrons and three dot-and-cross bonding pairs of electrons F321 Question 5 (b) (i) Answer + Two dot-and-cross bonding pairs of electrons and one dative covalent bond pair of electrons consisting of either two dots or two crosses (cid:57) One non-bonding pair of electrons AND which match the dative covalent bond pair of electrons (cid:57) 16<br />
F321 Mark Scheme January 2013 Question 5 (c) (i) Answer FIRST CHECK THE ANSWER ON ANSWER LINE IF answer = 7.624 OR 7.62 (g) award 3 marks Molar mass of borax = 381.2 (g mol1) (cid:57) Correctly calculates the mass of borax in 1000 cm3 = 0.0800 x 381.2 = 30.496 g OR 30.50 g OR 30.5g (cid:57) Correctly calculates the mass of borax in 250 cm3 = 30.496/4 = 7.624 g OR 7.62 g (cid:57) OR Molar mass of borax = 381.2 (g mol1) (cid:57) Amount of borax in 250 cm3 of solution = 0.0800 x 250 /1000 = 0.02(00) mol (cid:57) Mass of borax = 0.02(00) x 381.2 of borax = 7.624 g OR 7.62 g (cid:57) 17 Marks Guidance If there is an alternative answer, check to see if there is any ECF credit possible using working below ALLOW 381 DO NOT ALLOW 380 ALLOW 0.0800 x [molar mass of borax] correctly calculated for 2nd mark (ie mass of borax in 1000 cm3) ALLOW [mass of borax in 1000 cm3] / 4 correctly calculated for 3rd mark ALLOW calculator value or rounding to three significant figures or more IGNORE (if seen) a second rounding error ALLOW 381 DO NOT ALLOW 380 ALLOW [incorrect amount of borax] x 381.2 OR [incorrect amount of borax] x [incorrect molar mass of borax] OR 0.02(00) x [incorrect molar mass of borax] correctly calculated for this mark ALLOW calculator value or rounding to three significant figures or more IGNORE (if seen) a second rounding error<br />
F321 Question 5 (d) Answer (i) Correctly calculates the amount of borax used = 0.0800 x Marks Guidance Mark Scheme January 2013 (ii) Correctly calculates the amount of HCl used = 1.8(0) x 22.5/1000 = 1.8(0) x 103 mol OR 0.0018(0) mol (cid:57) 103 x 2 mol = 3.6(0) x 103 mol OR 0.0036(0) mol (cid:57) (iii) Correctly calculates the concentration of HCl = 3.6(0) x 103 / (25 / 1000) = 0.144 (mol dm3) (cid:57) ALLOW [incorrect amount of borax] x 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 ALLOW [incorrect amount of HCl] / (25/1000) correctly calculated for the 3rd mark given to 3 SF Total 12 18<br />](https://learnah.org/wp-content/uploads/2018/08/OCR_1_QP_JAN13_answer_5-0.jpg)
