Edexcel Jun 2016 (IAL) Paper 5 Q

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Answer ALL the questions. Write your answers in the spaces provided. SECTION C 23 Coloured substances Coloured substances, both natural and synthetic, have long been of interest to the human race. For example, there are over 130 minerals that have been used as gemstones. The corundum minerals, which include rubies and sapphires, are mainly aluminium oxide. Rubies have some of the aluminium ions replaced by chromium(III) ions and they range in colour from pink to deep red. Sapphires occur in many different colours including blue, yellow, purple, orange and green. Diamond is an allotrope of carbon. It is the hardest naturally occurring substance. Diamonds are often colourless but the presence of nitrogen atoms in natural diamonds gives them a brown or yellow colour, whilst the presence of boron gives them a blue colour. Dyes and pigments have been developed as colouring materials. Dyes are applied as a solution, whilst pigments are solids that are ground into a fine powder and made into a suspension with a suitable liquid. Methyl red is an azo dye and is used as an indicator. Its structure is CH3 CH3 COOH Prussian Blue, Fe4[Fe(CN)6]3, (discovered in 1704) is a deep blue colour and was one of the first synthetic pigments. It is used as a pigment in paints. Colour can arise in many different ways; for example, the colours seen in flame tests and in transition metal compounds. 24 *P46665A02432* D O N O T W R I T E I N T H I S A R E A D O N O T W R I T E I N T H I S A R E A D O N O T W R I T E I N T H I S A R E A<br /> A E R A S I H T N I E T I R W T O N O D A E R A S I H T N I E T I R W T O N O D A E R A S I H T N I E T I R W T O N O D (a) (i) Explain why complex ions containing chromium(III) ions are coloured. (4)(ii) Sapphires have the same type of structure as rubies. Suggest why sapphires and rubies have different colours. (1)*(b) Carbon exists as diamond and graphite. Explain, in terms of structure and bonding, why diamond is much harder than graphite. (3)*P46665A02532* 25 Turn over<br /> (c) (i) The standard enthalpy changes of combustion for diamond and graphite are shown below. C(diamond) + O2(g) (cid:314) CO2(g) (cid:507)H (cid:57) C(graphite) + O2(g) (cid:314) CO2(g) (cid:507)H (cid:57) c = 395.4 kJ mol1 c = 393.5 kJ mol1 Calculate the enthalpy change for the conversion of diamond to graphite. Use your answer to draw an enthalpy level diagram for the combustion of diamond and graphite. D O N O T W R I T E I N T H I S A R E A D O N O T W R I T E I N T H I S A R E A D O N O T W R I T E I N T H I S A R E A (2) (1) (ii) Explain which factor, other than enthalpy change, must be considered to show which allotrope is thermodynamically more stable.26 *P46665A02632*<br /> (d) The indicator methyl red, can be formed in two steps, starting from anthranilic acid. Step 1 NH2 COOH N+ (cid:119)N CI COOH anthranilic acid Step 2 methyl red COOH CH3 CH3 (i) State the reagents and condition needed for Step 1. (2)(ii) Step 2 involves a reaction which is similar to the reaction of diazonium ions with phenol. Suggest the structure of the organic compound which reacts with the diazonium ion in Step 2 to form methyl red. (1) A E R A S I H T N I E T I R W T O N O D A E R A S I H T N I E T I R W T O N O D A E R A S I H T N I E T I R W T O N O D *P46665A02732* 27 Turn over<br /> (iii) Use information from page 19 of the Data Booklet to suggest the type of acid-alkali titration for which methyl red indicator would be most suitable. Justify your answer. (2)(e) Prussian Blue contains the [Fe(CN)6]4 ion. (i) The [Fe(CN)6]4 ion is formed when aqueous potassium cyanide is added to an aqueous solution containing Fe2+ ions. Write the equation and state the type of reaction taking place when [Fe(CN)6]4 is formed in this way. (2) Type of reaction(ii) State the oxidation number of the iron ions shown in bold in Fe4[Fe(CN)6]3 (1)(Total for Question 23 = 19 marks) TOTAL FOR SECTION C = 19 MARKS TOTAL FOR PAPER = 90 MARKS 28 *P46665A02832* D O N O T W R I T E I N T H I S A R E A D O N O T W R I T E I N T H I S A R E A D O N O T W R I T E I N T H I S A R E A<br />

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