OCR A Jan 2009 Paper 1 Q2

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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 />

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