OCR A Jan 2009 Paper 1 Q2 (with explained solutions) |

Skip to content

OCR A Jan 2009 Paper 1 Q2

Answers available below

2 Chemists have developed models for bonding and structure which are used to explain different properties. (a) Ammonia, NH3, is a covalent compound. (i) Explain what is meant by a covalent bond.[1] (ii) Draw a dot-and-cross diagram to show the bonding in NH3. Show outer electrons only. [1] (iii) Name the shape of the ammonia molecule. Explain, using your dot-and-cross diagram, why ammonia has this shape and has a bond angle of 107. shape:explanation:[3]OCR 2009 Turn over<br />
(b) Ammonia reacts with hydrogen chloride, HCl, to form ammonium chloride, NH4Cl. NH4Cl is an ionic compound containing NH4 (i) Complete the electron configuration of the Clion. + and Clions. 1s2[1] (ii) Draw a dot-and-cross diagram to show the bonding in NH4 +. Show outer electrons only. [1] (iii) State the shape of, and bond angle in, an NH4 + ion. shape:bond angle:[2] (iv) A student investigated the conductivity of ammonium chloride. She noticed that when the ammonium chloride was solid it did not conduct electricity. However, when ammonium chloride was dissolved in water, the resulting solution did conduct electricity. Explain these observations.[2]OCR 2009<br />
(c) Ammonium compounds such as ammonium sulfate, (NH4 )2SO4, can be used as fertilisers. (i) Write a balanced equation to show how ammonium sulfate could be formed by the reaction between aqueous ammonia and sulfuric acid.[1] (ii) Ammonium sulfate is an example of a salt formed when an acid is neutralised by a base. Explain what is meant by the term salt.[1] (iii) Why is ammonia acting as a base in this neutralisation?[1] (iv) What is the relative formula mass of (NH4 )2SO4? Give your answer to one decimal place.[1] [Total: 15]OCR 2009 Turn over<br />

Show answer

January 2009 Additional Guidance ALLOW any response that communicates electron pair ALLOW shared pairs Must be dot-and-cross circles for outer shells NOT needed IGNORE inner shells Non-bonding electrons of N do not need to be shown as a pair. ALLOW bonds for bonded pairs DO NOT ALLOW atoms repel DO NOT ALLOW electrons repel ALLOW LP for lone pair ALLOW BP for bonded pair ALLOW subscripts IGNORE inner shells IGNORE + sign BUT a DO NOT ALLOWsign. Brackets and circles not required F321 Question 2 a i a shared pair of electrons (cid:57) Expected Answers Mark Scheme Marks ii (cid:57) iii Shape: pyramidal OR (trigonal) pyramid (cid:57) Explanation: There are 3 bonded pairs and 1 lone pair (cid:57) Lone pairs repel more than bonded pairs (cid:57) 1s22s22p63s23p6 (cid:57) ii 'Dot-and-cross' diagram to show four shared pairs of electrons one of which is a dative covalent bond (which must consist of the same symbols) (cid:57)<br />
F321 Question iii iv Expected Answers tetrahedral (cid:57) 109.5 (cid:57) ions OR electrons cannot move in a solid (cid:57) ions can move OR are mobile in solution (cid:57) i 2NH3 + H2SO4 (cid:198) (NH4)2SO4 (cid:57) ii when the H+ in an acid is replaced by a metal ion OR an ammonium ion OR a + ion (cid:57) iii accepts a proton OR accepts H+ (cid:57) iv 132.1 (cid:57) Total Mark Scheme Marks Additional Guidance ALLOW 109110 January 2009 15 ALLOW ions can move in liquid DO NOT ALLOW ions can move when molten ALLOW 1 mark for: Ions can only move in solution ALLOW 2NH4OH + H2SO4 (cid:198) (NH4)2SO4 + 2H2O ALLOW NH3 + H+ (cid:198) NH4 + ALLOW any correct multiple IGNORE state symbols ALLOW H for H+; ALLOW metal for metal ion i.e.: H in an acid can be replaced by a metal ALLOW donates a lone pair ALLOW removes H+ ALLOW forms OH ions IGNORE units NO OTHER ACCEPTABLE ANSWER<br />

Question 1 2 3 4 5

About us | Need Help? | Feedback

Proudly powered by WordPress | Theme: Sydney by aThemes.